tag:blogger.com,1999:blog-80585561148387970932024-03-13T23:18:32.938-07:00Neutrino Hunting in AntarcticaBerkeley Labhttp://www.blogger.com/profile/15717026573908295485noreply@blogger.comBlogger116125tag:blogger.com,1999:blog-8058556114838797093.post-58325019772196098882024-01-25T20:43:00.000-08:002024-01-25T21:17:33.068-08:00Citizen Scientists - and neutrinos<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEirdtsyfK8rCyxb2LtFaRbaVBVrfDK4FfYZ5DaKlD0tvF11oOIj41I0G9YzIe1OfZJNMAa1vPFiDuxpS5X7r1_U4gnjSdsFG8hbMRT-Bpt1DFDhM-po22CjgMt0a8NMmbH-bb80_Z3KWObsQyTMFkhK_sdC7OIdaZ3VVDWzrOukxoo05IkzEWQ3l8kqTi4/s1980/Signatures.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1228" data-original-width="1980" height="248" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEirdtsyfK8rCyxb2LtFaRbaVBVrfDK4FfYZ5DaKlD0tvF11oOIj41I0G9YzIe1OfZJNMAa1vPFiDuxpS5X7r1_U4gnjSdsFG8hbMRT-Bpt1DFDhM-po22CjgMt0a8NMmbH-bb80_Z3KWObsQyTMFkhK_sdC7OIdaZ3VVDWzrOukxoo05IkzEWQ3l8kqTi4/w400-h248/Signatures.png" width="400" /></a></div><br />Citizen-scientists have a long history; amateur astronomers have made many important discoveries, and, although opinions are mixed amateur archaeologists have brought many important sites to the attention of professionals. Now, citizen-science is moving into a new area: neutrino astrophysics.<p></p><p>Although neutrino telescopes are far beyond the reach of amateur scientists, their data is not. IceCube has enlisted the help of interested amateurs to help with a difficult pattern-recognition problem: classifying the types of neutrino interactions that IceCube sees. The figure above lists the different types classifications that are currently being considered. Distinguishing these classes of events is difficult for computer algorithms, but generally easier for people. </p><p>The program, called "Name that Neutrino" is hosted on Zooniverse, a web platform designed for citizen-science applications. A recent paper, "<a href="https://arxiv.org/abs/2401.11994" target="_blank">Citizen Science for IceCube: Name that Neutrino,</a>" discusses the program, and reports on the results of classifications by more than 1,800 volunteers. </p><p>All-in-all, a great way to teach science enthusiasts about IceCube and neutrino astronomy. <br /></p>
Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-25773470598545260032023-12-20T12:57:00.000-08:002023-12-20T12:57:21.254-08:00The mystery of the most energetic cosmic rays deepens<p style="text-align: justify;"> Recently, the <a href="http://www.telescopearray.org/" target="_blank">Telescope Array </a>(TA) Collaboration reported on the observation of a cosmic ray with enormous energy: 244 exa-electron volts (EeV, 2.44*10<sup>20</sup> eV), or roughly 40 Joules. This is one of a handful of events seen in this energy range - with an energy roughly comparable to a well hit tennis ball. Although this is not the most energetic particle ever seen, it is pretty close. </p><p style="text-align: left;"></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgjCW73LImVMY-2CJQ3vLXIzDZFAAEOFdfRzaBWBVydvUF2Rds6uzTPkbk-AfxNabGU0bSBO4InTq38XziircXXUpWMppQfdWhswHIWSz7J7j0Na9JW7G_Y2MxIiLrMRin8oHkmv9S4MTpn4BCPbjljB6frYx0-KyzDBq8MZ_Xv57JCbRiq_8csy-TLLL8/s1468/TAskymap.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="718" data-original-width="1468" height="314" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgjCW73LImVMY-2CJQ3vLXIzDZFAAEOFdfRzaBWBVydvUF2Rds6uzTPkbk-AfxNabGU0bSBO4InTq38XziircXXUpWMppQfdWhswHIWSz7J7j0Na9JW7G_Y2MxIiLrMRin8oHkmv9S4MTpn4BCPbjljB6frYx0-KyzDBq8MZ_Xv57JCbRiq_8csy-TLLL8/w640-h314/TAskymap.png" width="640" /></a></div><span style="font-family: helvetica; font-size: small;"><b>Fig. 1.</b> A skymap, showing the best-estimate directions for the event, after correcting for expected deflection in galactic and extra-galactic magnetic fields. The labelled circles are the best estimates for different assumptions about nuclear composition, from protons (p) through iron (Fe) for two different models of the galactic magnetic fields - PT2011 and JF2012 which predicts larger deflections . The active galaxy PKS1717+177 is a flaring source, but it is 600 Mpc away - probably too far to be the source of this event. Also shown is a broad hotspot previously seen by TA at lower energies, along with the galactic plane (the solid line), with the galactic center also indicated. </span><br /><p></p><p> </p><p style="text-align: justify;"> The intriguing thing about this event is its direction. The arrival direction was measured to better than 1 degree. Fig. 1 (above) shows the predicted arrival direction. At these energies, cosmic rays are not expected to bend very much in galactic and intergalactic magnetic fields. The TA Collaboration calculated the expected bending for different hypotheses about the nuclear species of the incident particle, from protons to iron, and accounted for that bending. Then, they looked in that general direction, and found nothing that seemed likely to be able to accelerate particles to those energies. Because 250 EeV particles can interact with the cosmic microwave background radiation and lose energy, their range is limited to 10-30 megaparsecs (Mpc), depending on nuclear species. The active galaxy PKS1717+177 was considered as a source, but, at 600 Mpc distance, is too far to be a likely source.<br /></p><p style="text-align: justify;">This is a finite volume for a possible source, and it was devoid of 'interesting' objects. 'Interesting objects' include active galactic nuclei (galaxies with supermassive black holes at their center, with significant accretion which leads to a relativistic jet) and other sites that may contain the ingredients for a powerful particle accelerator. <br /></p><p style="text-align: justify;">There are a couple of possible explanations for the lack of an apparent source - all interesting. It may be that we need to expand our definition of what is 'interesting' here - the accelerating sites are something that we have not thought of. Or, maybe, the accelerators do not leave obvious other traces, or are distributed in space. Or, possibly, the galactic and/or intergalactic magnetic fields are significantly larger than we expect. </p><p style="text-align: justify;">As the name implies, the Telescope Array is an array of surface scintillator detectors (to detect charged particles in cosmic ray air showers) and fluorescence detector telescopes to detect the fluorescence from nitrogen in the air as these charged particles propagate through the atmosphere. <br /></p><p style="text-align: justify;">The paper was <a href="https://www.science.org/doi/10.1126/science.abo5095" target="_blank">published in Science</a>, but is also <a href="https://arxiv.org/abs/2311.14231" target="_blank">freely available on the arXiv</a>. <br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-40297584305072857622023-07-17T20:37:00.004-07:002023-07-17T20:37:48.450-07:00Neutrinos from our galaxy<p> IceCube has found a new source of neutrinos - our own Milky Way galaxy, with a significance of 4.5 sigma! This observation was published in <a href="https://www.science.org/doi/10.1126/science.adc9818">a recent paper in Science</a>; <a href="https://arxiv.org/pdf/2307.04427">a freely available version is available on the arXiv. </a>This study is both technically and scientifically very different from the two observations of neutrinos from active galactic nuclei (AGN) that IceCube previously observed.<br /></p><p>Earth is within the Milky Way, which is, from our observation point, largely a plane in space so the source surrounds us. High-energy gamma-rays have been observed coming from the Milky Way The line has a width of a couple of degrees, depending on how you define the width. This is very different from other galaxies, which are point sources (or close to that); the different geometry calls for a different analysis technique. Instead of using muons from muon-neutrinos, this study used `cascades,' which come from electron-neutrinos, and neutral-current interactions of all neutrino flavors. The advantage of using cascades is that the background of atmospheric neutrinos is much lower, so the signal:noise ratio is higher. The disadvantage is that the angular resolution isn't nearly as good. However, IceCube used a machine-learning technique, a convolutional neural network (CNN), to determine cascade directions. A CNN works in a roughly similar manner to our own brains, with neuron-like processing steps that looked at the light deposition in IceCube's sensors. This approach gives a resolution that is about two times better than previous cascade directional studies, lessening the difference with nu_mu's. And, it used many more events. since the Milky Way is not a point source, the angular resolution is less important. The figure below shows how the analysis was done:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3-Sh2nh5EgK8atKGw9cZSJBzcfiwjEFaDB3LYNULaiH3yrTDW-VE8Y7G0U280MyRCQ5jlJ1flqEFsK34P_0UqQdH_65PfBmC-3UiBjHd4PRcngoAQ4Kx7soS5DqjMinbn6FLkw7CJXuGNzDiNBxm70Mq3x7q73ZMPqyntPk62_22H4TDbTcIclcOQu8o/s1874/Galaxyinnu.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="900" data-original-width="1874" height="193" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3-Sh2nh5EgK8atKGw9cZSJBzcfiwjEFaDB3LYNULaiH3yrTDW-VE8Y7G0U280MyRCQ5jlJ1flqEFsK34P_0UqQdH_65PfBmC-3UiBjHd4PRcngoAQ4Kx7soS5DqjMinbn6FLkw7CJXuGNzDiNBxm70Mq3x7q73ZMPqyntPk62_22H4TDbTcIclcOQu8o/w400-h193/Galaxyinnu.png" width="400" /> </a></div><div class="separator" style="clear: both; text-align: justify;"><span style="font-size: x-small;">The Milky Way, seen in different ways. The galactic center is in the middle. The images extend +/- 15 degrees from the galactic plane., and cover the full 360 degree panorama. The top panel is a composite optical image of the Milky Way. The second panel down show the Milky Way as seen by the Fermi satellite Large Area Telescope, using photons with energies above 1 GeV. The third panel shows a template developed from the Fermi data, assuming that the photons come from π<sup>0</sup> decays. The fourth panel shows a template for what IceCube should see, after accounting for angular resolution and other detector effects. Finally, the bottom panel shows the neutrino observations. </span></div><div class="separator" dir="rtl" style="clear: both; text-align: justify;">. <br /></div><p>The other interesting thing about the neutrinos from the Milky Way is that we are in the galactic plane. This is very different from the previous observations, of neutrinos from <a href="https://arxiv.org/abs/2211.09972">NGC1068</a> and <a href="http://antarcticaneutrinos.blogspot.com/2018/07/found-one-cosmic-accelerator-txs050656.html">TXS0506</a>, both of which are AGNs, with considerable high-energy activity. We are also observing them from relatively close to their axis of rotation, where high-energy emission is more likely. In contrast, we are in the plane of the Milky Way, and it appears that the neutrinos are coming from many directions. </p><p>IceCube found that the neutrino emission was consistent with the pattern of photon emission, assuming that the photons came from pi^0 and neutrinos come from charged pions. However, the measured neutrino flux was considerably higher than one would expect based on pi^0 extrapolations. There could be several reasons for this, including photon absorption en-route to Earth. The neutrinos and pi^0 might be produced in sources, of when high-energy cosmic-rays interact with atoms or dust while moving around the galaxy. However, a<a href="https://arxiv.org/pdf/2307.07576"> very recent new search</a> for emission from a number of known sources of energetic (TeV) gamma-rays did not find evidence for an excess of neutrinos. In short, this is an important observation that raises many interesting new questions. <br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-35098191278422729582023-02-22T17:28:00.000-08:002023-02-22T17:28:11.105-08:00Scientists behaving badly? In Antarctica?<p> Over the past decade, sexual harassment (and other related bad behavior) has become a hot topic among scientists, and everyone - employers, government agencies, and scientific societies are (properly) under pressure to take action to combat it. Although almost everyone agrees that something must be done, the details are not always simple. </p><p>This is especially true in Antarctica, where the problem is enormous, and solutions may be hardest. In September, the NSF released a comprehensive report (<a href="https://www.nsf.gov/geo/opp/documents/USAP%20SAHPR%20Report.pdf" target="_blank">available here</a>) which documented the scale of the problem, and gave some thoughts about the solution. A survey provided hard data, which backed up many quotes from interviews. It all made for some very disturbing reading. Briefly, women (and some men) were broadly harassed, and there was often little that was done about it. One interviewee said "“Every woman I knew down there had an assault or harassment experience that had occurred on ice...” Another said "It's so self-evident that [it's] barely work speaking out loud. [Sexual assault and sexual harassment] are a fact of life [here], just like the fact that Antarctica is cold and the wind blows." Another quote describe a male supervisor attempting to break into a women's bedrooms using his master keys, and still another described a violent sexual assault. <br /></p><p>The report also touches on some of the reasons that the problem is both so painful for victims, and also hard to fix. First, there is no single person in charge. People at the U. S, Antarctic bases work for many different employers - universities and national labs in multiple countries, one of multiple logistical contractors, the U. S. Air Force and the New York National Guard, to name a few. It can be difficult to figure out who someone works for, much less how to complain to their employer. People also come from a variety of backgrounds - scientists are in the minority. <br /></p><p>Second, it is very isolated, both physically and psychologically. Communications bandwidth (both phone and internet) is very limited, and most workers at McMurdo station have limited access to the outside world. So, even if there was a clear address to complain to, it would not be easy to do so. And, it would be almost impossible for any outside agency to investigate happenings in Antarctica. And, even when there is access, the rest of the world is so distant, and engagement doesn't seem important.<br /></p><p>Third, there is a significant gender imbalance. This is partly (but only partly) a self-perpetuating complication, since the toxic atmosphere in Antarctica discourages many women from applying for jobs there, worsening the imbalance. <br /></p><p>The problem of reporting, at least, has a fairly simple solution. There needs to be offices, in McMurdo, and some of the other large bases, where people can report problems, which will then be investigated by people who are stationed there. The NSF cannot fire people directly, but they should be able to quickly remove people from Antarctica when needed. This will not solve every problem - it may not be practical to have relevant offices in small field camps, but there hopefully the camp managers should be on top of things (unless they are unfortunately part of the problem). The U. S. military may be another issue - I do not have any clear knowledge that they are part of the problem, but they are clearly a law unto themselves, and military personnel were not allowed to participate in the survey until it was too late. Still, this would provide a clear reporting path for 90% of the problems. </p><p>Such a reporting system would pay significant dividends beyond reducing the amount of sexual harassment and assault. Improving the atmosphere would increase the applicant pool for Antarctic jobs, and should lead to a better work force, and, hopefully, a happier one.</p><p>From what I can see, the NSF took the report seriously. And, many of the groups that send people to Antarctica (IceCube included) are also making changes. Unfortunately, so far, changes have been limited. <a href="https://arstechnica.com/science/2023/02/as-antarctic-fieldwork-ends-a-sexual-harassment-reckoning-looms/">A recent Ars Technical article </a>discusses some of the changes - including a confidential advocate that victims can talk to - but clearly more drastic changes are needed. <br /></p><p><br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-61874352314423513272023-01-22T23:01:00.001-08:002023-01-22T23:01:47.309-08:00Elections as measurements<p>
</p><p class="MsoNormal"></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrgw3OIz9aafHsSiiCjGFP4SD-Qw96GvTQ3Uoo8sx4Z-RqEDsGaE6P3cfZpRiMwaGNwrjz8nPBX6_B6mX2evKwakWmtOAerJ58Cp0YM5h6eKoUiYytzM4kiP4SrO-Qhc67kQ9GakguvYAyA8mwnB8MB0AQFLaMm7BEiscZvEQILW-L5cvnRasAe52e/s1576/Screen%20Shot%202023-01-22%20at%2023.03.20.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1232" data-original-width="1576" height="250" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrgw3OIz9aafHsSiiCjGFP4SD-Qw96GvTQ3Uoo8sx4Z-RqEDsGaE6P3cfZpRiMwaGNwrjz8nPBX6_B6mX2evKwakWmtOAerJ58Cp0YM5h6eKoUiYytzM4kiP4SrO-Qhc67kQ9GakguvYAyA8mwnB8MB0AQFLaMm7BEiscZvEQILW-L5cvnRasAe52e/s320/Screen%20Shot%202023-01-22%20at%2023.03.20.png" width="320" /></a></div><br />The complete debacle in the recent (Nov. 8<sup>th</sup>,
2022) election for the <a href="https://www.ousd.org/domain/63" target="_blank">Oakland School Board (OSB)</a> led me to think more about
elections.<span style="mso-spacerun: yes;"> </span>For those of you who are from
outside the San Francisco Bay Area, after tabulating and announcing the election results,
the Alameda County registrar found an error in how ballots were counting, and On
Dec. 28<sup>th</sup> announced a new top vote-getter, less than two weeks before
inauguration day.<p></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Oakland is a city of about 440,000 people just south of
Berkeley (where I live).<span style="mso-spacerun: yes;"> </span>The OSB is
important, since Oakland schools are facing <a href="https://oaklandside.org/2022/12/08/oakland-school-closures-school-board-election/">many problems, </a>including declining
enrollment, educational recovery from Covid closures, and financial
problems.<span style="mso-spacerun: yes;"> </span>The OSB election used rank
choice voting, so counting took time; <a href="https://oaklandside.org/2022/12/01/how-well-did-ranked-choice-voting-work-in-the-2022-oakland-mayors-race/" target="_blank">the results were announced by early
December.<span style="mso-spacerun: yes;"> </span>Nick Resnick won in District
5.</a><span style="mso-spacerun: yes;"><a href="https://oaklandside.org/2022/12/01/how-well-did-ranked-choice-voting-work-in-the-2022-oakland-mayors-race/" target="_blank"> </a> </span>This result was duly certified. <span style="mso-spacerun: yes;"> </span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Then, on December 28<sup>th</sup>, the registrar dropped a
<a href="https://oaklandside.org/2022/12/28/alameda-county-registrar-miscounted-ballots-oakland-election-2022/">bombshell.</a><span style="mso-spacerun: yes;"> </span>There was a mistake in
tabulating ranked choice votes, and a different candidate, Mike Hutchinson, was
the actual top vote getter.<span style="mso-spacerun: yes;"> </span>Some voters
did not select a first-choice candidate, but did select ones for second or
third choice.<span style="mso-spacerun: yes;"> </span>Those second or third
choices should have been tabulated when the ranked choice algorithm got to the
second or third choice, but they mistakenly were not counted at all.<span style="mso-spacerun: yes;"> </span>This was pointed out by a non-profit that
looked over the voting results and spotted a problem.<span style="mso-spacerun: yes;"> </span>When this was fixed, the District 5 results
changed.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Despite this bombshell, the originally-certified winner, <a href="https://oaklandside.org/2023/01/09/oakland-school-board-inauguration-overshadowed-by-election-mishap/" target="_blank">Nick
Resnick was sworn in to office on Monday (Jan. 9<sup>th</sup>)</a>.<span style="mso-spacerun: yes;"> </span>The ultimate disposition is in the hands of
the courts, since <a href="https://www.ktvu.com/news/election-error-that-flipped-oakland-school-board-race-goes-to-court">Hutchinson has, not surprisingly, sued</a>.<span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span>The
first hearing will be in May, after many OSB meetings and votes. </p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">What does this have to do with physics?<span style="mso-spacerun: yes;"> </span>Elections can be considered measurements of
the will of the people.<span style="mso-spacerun: yes;"> </span>Some measurements
give very clear results, while others are ambiguous.<span style="mso-spacerun: yes;"> </span>Like measurements, elections have statistical
and systematic uncertainties.<span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">The statistical uncertainties are from random fluctuations
in who did or did not vote. If the election were rerun, some different people
would vote, because they were sick that day, or out of town, or just forgot. <span style="mso-spacerun: yes;"> </span>Further fluctuations come from the lag in
voting when people move into or out of the district, turn 18, or pass away. Mail-in
ballots change the details, but not the overall picture – fluctuations remain.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">From the measurement analogy, the statistical fluctuations
are roughly the square root of the number of voters.<span style="mso-spacerun: yes;"> </span>If 100,000 people cast votes then the
uncertainty is the square root of 100,000, or 316 votes.<span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span>There are other, more sophisticated (binomial)
formulae, but this is a reasonable estimate.<span style="mso-spacerun: yes;">
</span>Elections with a smaller vote difference could easily have gone the
other way.<span style="mso-spacerun: yes;"> </span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Systematic errors may be larger, and stem from systemic
issues, such as the OSB debacle.<span style="mso-spacerun: yes;"> </span>One
difficulty with the analogy is that not everybody agrees on what ‘features’ of
our election system are systematic uncertainties and which are ‘the rules.’ <span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span>Funding
inequity and unwarranted voter suppression are both major issues which can lead
to unfairness, and incumbents certainly have advantages.<span style="mso-spacerun: yes;"> </span>It is a matter of defining the question we ask.<span style="mso-spacerun: yes;"> </span>Are we measuring ‘the peoples will, according
to rules, or ‘the peoples will, as would be measured in a perfect, unbiased
system?<span style="mso-spacerun: yes;"> </span>The problem with the latter choice
is that people disagree about the biases.<span style="mso-spacerun: yes;">
</span>‘According to the rules’ is a clearer baseline. <a href="https://nyujlpp.org/wp-content/uploads/2012/11/Stephen-Ansolabehere-Nathaniel-Persily-Measuring-Election-System-Performance.pdf">Methodologies exist</a> to try to estimate biases for the latter case.<br /></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Either way, though, when elections are within the combined
error, the vote counts are statistically indistinguishable.<span style="mso-spacerun: yes;"> </span>This is not to say that the different
candidates are similar, or that partisans on both sides will not feel strongly
about the result.<span style="mso-spacerun: yes;"> </span>But, there is no discernible difference in the people’s preferences. </p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Treating elections as experimental measurements can help put
their results in perspective.<span style="mso-spacerun: yes;"> </span>a 51%:49%
split is not a mandate, but a small, and perhaps statistically insignificant
difference. <span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span>Successful candidates will govern better if
they keep this in mind. </p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">The opinions expressed here are my own, and not necessarily those
of my employer, colleagues, family, friends, or anyone else (although they
should be).<span style="mso-spacerun: yes;"> </span></p>
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{page:WordSection1;}</style></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-86734159670871612442022-12-22T13:30:00.002-08:002022-12-22T13:30:08.825-08:00Cool visualization<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhzZDUPFme-yfhCyv0jcaL1D7YjI_3ziQH31ds3ZGx-QT-7a8wdD9dGocSn2csKtnXK7yGbC0xoo-A_OrEC5cIJXtyMMGGbqsN05EiVd8M6V7KUpdAQtkVclboe8tN-URmJD6xtbEKI5pwZPwkrVIHkeM7N5mlsM8Gz2fxlj_z4T48qtUsCnZVqhos3/s2340/Neutrinosentering%20theEarth.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1770" data-original-width="2340" height="242" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhzZDUPFme-yfhCyv0jcaL1D7YjI_3ziQH31ds3ZGx-QT-7a8wdD9dGocSn2csKtnXK7yGbC0xoo-A_OrEC5cIJXtyMMGGbqsN05EiVd8M6V7KUpdAQtkVclboe8tN-URmJD6xtbEKI5pwZPwkrVIHkeM7N5mlsM8Gz2fxlj_z4T48qtUsCnZVqhos3/s320/Neutrinosentering%20theEarth.png" width="320" /></a></div><br /> Some members of IceCube (led by Lu Lu, at UW Madison) have created <a href="https://user-web.icecube.wisc.edu/~lulu/globe_AR/webcity/ngc1068/">a cool new visualization for IceCube events.</a> It shows where the neutrinos that reach IceCube entered the Earth (only upward-going muon neutrinos are shown). The Earth can be rotated, and it is possible to set the minimum energy. These are mostly atmospheric neutrinos, so are distributed over the Earth, but it is still possible to see some interesting things. <p></p><p>In the screen-capture above, with an energy threshold of 100 TeV, it is clear that the neutrinos are predominantly in the Southern hemisphere. This is because, at these energies, most neutrinos are absorbed in the Earth, so, with their longer trajectories through the Earth, most Northern hemisphere neutrinos are absorbed before reaching IceCube. <br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-17934556659302025652022-11-20T21:34:00.001-08:002022-11-20T21:34:10.412-08:00More on Science in the age of Ukraine<p> I wanted to give you an update on how international science (CERN, in particular) has been reacting to the continued Russian invasion of Ukraine. The invasion is now in its 8th month, and the four large LHC experiments still have not decided how to publish papers with author lists, affiliations and acknowledgements of funding agencies that reflect that fact. Papers from the LHC experiments are being sent to the Cornell arXiv with the authors listed as <a href="https://arxiv.org/abs/2211.04384">"The ALICE Collaboration,"</a> without lists of individual authors, institutional affiliations, or acknowledgements to the funding agencies. <br /></p><p>The papers are also being submitted to diverse scientific journals for review, with the understanding that versions with author lists, affiliations and acknowledgements will be forthcoming, hopefully allowing for timely publication. Unfortunately, after 8 months, it is clear that the 'timely' part of this is not happening, and it is likely that some journals are becoming less happy about the situation. They do best on a steady diet of publications. It will not be easy for them to deal with a brief flood of manuscripts that are ready for publication once the author lists, etc. arrive. </p><p>This will also not make things easier for some of our younger colleages who may be in the job market. Everybody involved in CERN is well aware of the situation. However, although the collaborations are making every effort to document their contributions, not having actual published papers may not make things easier farther afield, either in smaller institutions where one interviews with people in other subfields of physics, or in industry. <br /></p><p>CERN, for its part, has not taken further visible action, with the last pronouncement being <a href="https://home.cern/news/news/cern/cern-council-responds-russian-invasion-ukraine">their March 8th announcement.</a> <br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-82653161903998139942022-11-20T21:21:00.002-08:002022-11-20T21:21:34.132-08:00A new source of astrophysical neutrinos<p> </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhT0gkN1qPDcFeD0Wlkv0eJfOrjBUAMTFZhZpSLUYMw7RcRfGhBsYyxoSA_RF1zi-dCdyRyMGJtxMHWZsIpRos4VNjFJAvoJi6B1103tloqRpFmZ1aIv52j5hI-qF_5m8k8p3qe1qsD9UXuIsvLUEQmQ0GkMjRPmFMeRubryqdVEtpPrUx1EuswimbN/s2400/NGC1068.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="2400" data-original-width="2320" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhT0gkN1qPDcFeD0Wlkv0eJfOrjBUAMTFZhZpSLUYMw7RcRfGhBsYyxoSA_RF1zi-dCdyRyMGJtxMHWZsIpRos4VNjFJAvoJi6B1103tloqRpFmZ1aIv52j5hI-qF_5m8k8p3qe1qsD9UXuIsvLUEQmQ0GkMjRPmFMeRubryqdVEtpPrUx1EuswimbN/s320/NGC1068.png" width="309" /></a></div>A likely new source of astrophysical neutrinos has been identified! In a paper <a href="https://www.science.org/stoken/author-tokens/ST-839/full">published in Science</a>, the IceCube Collaboration reported on the observation of neutrinos coming from an object called<a href="https://en.wikipedia.org/wiki/Messier_77" target="_blank"> NGC1068,</a> with 4.1 sigma significance. The probability that this is a random statistical fluctuation is about 1.1 in 100,000. This calculated significance accounts for the fact that this was part of a search for neutrinos from 110 likely sources that were studied - this is known as correcting for trial factors - essentially the number of experiments that were tried at once. A version of the paper is also available <a href="https://arxiv.org/abs/2211.09972">here, on the Cornell arXiv preprint server)</a>. <br /><p></p><p>NGC1068 (also sometimes known as M77) is an Active Galactic Nucleus (AGN) about 47 million light years from Earth. AGNs are spiral galaxies with supermassive black holes at their center. These black holes accrete (pull in) matter from the surrounding galaxy; in the process, some of the matter is ejected at relativistic velocities (speeds a fair fraction of the speed of light) in a collimated jet that follows the axis of rotation of the galaxy. NGC1068 is one of the closer AGNs, so it is not too surprising that it should be one of the first (<a href="http://antarcticaneutrinos.blogspot.com/2018/07/found-one-cosmic-accelerator-txs050656.html">after TXS0605+56</a>) high-energy astrophysical neutrino sources to be observed. The signal was composed of about 80 neutrinos over the background, which was mostly atmospheric neutrinos. The figure above shows the position of the hotspot (including contours corresponding to 68% and 90% positional uncertainty) compared with that of NGC1068, denoted by the red star. The agreement is good, and there are no other likely sources within the error contours. <br /></p><p>NGC1068 was first seen in an earlier IceCube paper, published in 2020 in <a href="https://doi.org/10.1103/PhysRevLett.124.051103">Physical Review Letters</a> (also freely available <a href="https://arxiv.org/abs/1910.08488">here, from the Cornell arXiv</a>). That paper used 10 years of data, and observed NGC1068 with a significance of 2.9 sigma. The higher significance came from a couple of factors: more new data (and some old partial-detector data was dropped), improved calibrations, and an improved analysis method. Going from 2.9 sigma to 4.1 sigma is a pretty significant improvement for a re-analysis like this; it seems that the largest single factor was the improved calibrations.</p><p>Assuming that this holds up (it is not over the 5 sigma threshold ), this will be the second neutrino source seen by IceCube. Both are AGNs, so those of us who are impatient can see a pattern developing. That said, there are differences. TXS0506 is much further away - 5.6 billion light years. It is a known source of gamma-rays, while NGC1068 is not - it's jet is surrounded by a dust cloud that would obscure X-rays and gamma-rays. And, neutrino emission from TXS0506 was associated with a period exhibiting an increase in gamma-rays, while the NGC1068 source is steady state (at least we have not seen evidence for variability). <br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-76783190241189536792022-08-14T13:35:00.003-07:002022-08-14T13:35:30.164-07:00STAR Trek medicine: coming soon to a doctor near you?<p><a href="https://en.wikipedia.org/wiki/Star_Trek">Star Trek</a> is full of cool science-fictiony gadgets, most of which are far beyond the understanding of todays science. Today, I wanted to write about a new development that now seems related to one of these devices - Star Trek's <a href="https://memory-alpha.fandom.com/wiki/Dermal_regenerator">dermal regenerator.</a> Dermal regenerators are hand held devices that can be held over cuts, wounds, burns etc. to repair the damage. Now, a paper in Science magazine has reported on a technique that is at least a small step in that direction. The paper is Z. Ma et al., Science 377, 751 (2022); unfortunately, Science has a new system for subscribers that defeats my ability to provide a URL. <br /></p><p>Today, surgeons seal incisions (either surgical or wounds) using sewing (stitches) or staples. It works, but is inelegant, and since it involves additional piercing of the skin around the wound, it causes some additional damage. A worthwhile tradeoff, but not optimal, so doctors have been searching for an alternative.</p><p>Adhesives are one obvious alternative, but they have unfortunate limitations which have prevented their use. In short, living tissue is wet, slippery and pliable - three factors that are difficult for glues. Pliability is a special problem, since it requires an adhesive that is equally pliable - even after setting. Otherwise, when the recipient moves, the wound will tear open again. So far, no workable option has been found. </p><p>Now, the Science paper presents a method of using ultrasound to get adhesives to set quickly and strongly. It starts by adding a solution containing polymers to the wound. Polymers are long-chain hdyrocarbons that have a tendency to cross-bond with each other. Think plastics. This is followed by a hydrogel. Then, ultrasound is applied - this is where a dermal regenerator like device comes in - this could be a hand held unit waved over the wound. The ultrasound performs a couple of functions. It drives the polymers deeper into the wound. And, it causes them to spread out and cross-link, forming a strong but flexible network to hold the wound together. Voila - Star Trek in the 21st century.</p><p>It turns out that I am not the only one to make the connection between recent medical developments and a dermal regenerator. Julia Simpson wrote about <a href="https://lions-talk-science.org/2021/04/22/chasing-the-dream-of-the-dermal-regenerator/">some different possible approaches</a> toward a dermal regenerator about a year ago. She proposed three possibilities, all of which involve adding something to the wound: a matrix of silkworm and spider silk, a specially made biomaterial, and a hydrogel scaffold that would alter the immune system to improve healing. However, none of these seem to require a handheld device - the need for ultrasound makes this new development closer to a true dermal regenerator. <a href="https://www.startrek.com/news/star-trek-dermal-regenerator-mobile-skin-bioprinter">Another approach,</a> which seems closer to that depicted in Star Trek, would be to use a bioprinter to essentially print replacement tissue to fill in the wound. </p><p>Of course, all of these ideas are quite some distance from routine use in a doctors office or hospital. And, I should note that I am not a medical doctor, so take this with a grain of salt (or, this being Star Trek, a grain of quadrotriticale). But, it seems like a really cool idea, and hopefully it will pan out. <br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-43389379349786095502022-08-14T13:02:00.003-07:002022-08-14T13:02:46.139-07:00Imaging the Earth with Neutrinos<p> Hi again,</p><p>As the Russian invasion of Ukraine continues (with, to my mind, uncertain results), the four CERN LHC experiments still have no agreement on papers with Russian co-authors. Since early March (6 months ago), the experiments have been submitting papers to the <a href="https://arxiv.org/">Cornell preprint server </a>with only collaboration names - no individual authors. These 'nameless' papers are being refereed by journals, and doubtless some of them are ready for publication, lacking only a specific list of author names, and likely affiliations. </p><p>The world of neutrino astronomy has also been pretty quiet. The RNO-G deployment season in Greenland is winding down, apparently quite successful. There was an interesting two-day (<a href="https://indico.fnal.gov/event/53004/timetable/#20220730.detailed">Saturday</a> and <a href="https://indico.fnal.gov/event/53004/timetable/#20220731.detailed">Sunday</a>) meeting at "NuFact 2022" on the use of neutrinos to image the interior of the Earth. There are two techniques that can be used. The first is to look for neutrino absorption in the Earth, as we have discussed before. The second is to study neutrino interactions with the electrons in the nuclei in the Earth. These electrons are seen as effectively a large cloud, and electron-flavored neutrinos interact with the cloud differently than muon-flavored and tau-flavored neutrinos. This affects how neutrinos oscillation - this is known as matter-induced oscillations. The affect depends on the electron density, so oscillations can serve as a complementary approach to neutrino absorption. <br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-66605104443256648882022-07-05T21:31:00.007-07:002022-07-05T21:31:59.896-07:00Ukraine, Russia and Astrophysics<p style="text-align: left;">My posts about scientists' response to the Russian invasion of Ukraine have been mostly focused on particle physics, since CERN has notably struggled to craft an appropriate response. Nowhere else is the conflict between science as a driver of international cooperation, and the need to stand up against an immoral invasion so stark. </p><p style="text-align: left;">But, other physicists have also faced conflicts over this. In high-energy neutrino astrophysics, there was less collaboration between Russian and Western scientists, but there were still many discussions about appropriate responses. </p><p style="text-align: left;">IceCube had no members whose primary affiliation was Russian. Two IceCube physicists had secondary affiliations with Moscow Engineering Physics Institute, but they both dropped these connections shortly after the invasion. <br /></p><p style="text-align: left;">The Baikal-GVD experiment (in Lake Baikal) was almost entirely Russian collaborators. Some long-time collaborators from what used to be East Germany dropped out. Both the Baikal-GVD and IceCube responses were made relatively quietly. <br /></p><p style="text-align: left;">In contrast, the mostly-European KM3NeT collaboration (building two arrays in the Mediterranean) has taken a public stance. They have had Russian collaborators in past years, but do not appear to do so now. Nevertheless, they made a clear statement to #StandwithUkraine, suspending all institutional cooperation with science organizations in Russia. Their statement, highlighted on <a href="https://www.km3net.org/">their main web page </a>is nicely nuanced, continuing "We deeply believe that science is to serve peace and understanding, and we therefore leave private communication channels open to our colleagues with Russian affiliation, of whom many have stood up against the war." <br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEg3q8TLtRutEV7ygb5igFnIo0l1T1rESqRqHR3qJEdMueWDXhfQyRxfa3-yopPnkc34v8DTaPJcqtzBSdjvhP8y2x2d6NXbNQHA0cyBYQCNbFGf4NLcFvAszOiHietIQkFomvXhx27Mh8yoGrHutTXDebVm3W0NPKuVSsBLJldDL7lNtx0vocvu51OT" style="margin-left: 1em; margin-right: 1em;"><img alt="" data-original-height="768" data-original-width="1024" height="240" src="https://blogger.googleusercontent.com/img/a/AVvXsEg3q8TLtRutEV7ygb5igFnIo0l1T1rESqRqHR3qJEdMueWDXhfQyRxfa3-yopPnkc34v8DTaPJcqtzBSdjvhP8y2x2d6NXbNQHA0cyBYQCNbFGf4NLcFvAszOiHietIQkFomvXhx27Mh8yoGrHutTXDebVm3W0NPKuVSsBLJldDL7lNtx0vocvu51OT" width="320" /> </a></div><div class="separator" style="clear: both; text-align: center;"> Photo: a KM3NeT string, waiting for deployment. Credit: KM3NeT Collaboration.</div><div class="separator" style="clear: both; text-align: center;"> </div><div class="separator" style="clear: both; text-align: left;">The Global Neutrino Networks newsletter, edited by Christian Spiering (from DESY-Zeuthen, near Berlin) has done a very nice job of covering the astrophysicists response to the Russian invasion. Back issues of the newsletter are available <a href="https://www.globalneutrinonetwork.org/e227156/">here. </a><br /></div><br /> <br /><p></p><p><br /></p><p><br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-70804850832594380962022-06-17T14:19:00.004-07:002022-06-17T14:19:54.561-07:00CERN and Russia break up<p> At this week's meeting, <a href="https://home.cern/news/news/cern/cern-council-cooperation-agreements-russia-belarus">the CERN Council did what many people expected: effectively ejected Russia and Belarus. </a> This was done somewhat more softly than had been expected, since, rather than acting immediately, the Council would not extend their cooperation agreements when they expire in 2024. This was a compromise, since many people had been pushing for faster action. 2024 is far off. The statement was accompanied by the expected text denouncing the Russian invasion, but it still seems like an attempt to put off any real action. </p><p>It will also not solve the authorship problems faced by the large LHC Collaborations (and likely by smaller groups), where some European funding agencies (most notably the Germans and the Poles - see my previous posts) have told their grantees to stop collaboration with Russian institutions. And, of course Ukrainian scientists are generally doing this of their own volition. There may have been some quiet agreement with the European funding agencies, but this will still feel like a slap in the face to the Ukrainian scientists who work at CERN. As I noted in a previous post, I have enormous sympathy for my Russian colleagues, many of whom expressed their opposition to the war when they could legally do so. But still, if it comes down to a decision between accommodating scientists from the invaded country or those from the invaders country, my sympathy is clearly with the invaded country. </p><p>On the other hand, <a href="https://www.aps.org/policy/statements/guidlinesethics.cfm">scientific ethics require giving appropriate scientific credit to the people who did the work.</a> In large collaborations, this is rule-based - when you join an experiment you have to contribute a certain amount of service work (work to keep the experiment running), take data-collection shifts, etc., and, after a certain amount of time, you are added to the author list for all papers, along with 900-3,000 of your closest colleagues. For example, the ALICE experiment (at the LHC) experiment rules are available <a href="https://alice-collaboration.web.cern.ch/sites/default/files/Documents/AnnexF_ALICEPublicationPolicy_Adopted29November2019.pdf">here. </a> Usually, 6 months or a year after you leave the collaboration, you are removed from the author list. Neither the general principles of scientific ethics nor these collaboration-based rules contain exceptions for cases when the workers employers behave unacceptably. <br /></p><p>Authorship questions are likely to come up again as the CERN Council decision rattles down to the four LHC experiments, who will need to decide how to handle their author lists. This will also likely result in a compromise of some sort. One possibility which I like would be to list the scientists from Russian institutions on the author list, but not list their institutional affiliations. <br /></p><p><br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-67673701504053523982022-05-07T22:12:00.000-07:002022-05-07T22:12:23.274-07:00Reactions to Ukraine from the world of science<p>The Russian invasion of Ukraine has now continued for more than two months, and no end is in sight. Instead of ending the war on May 9th, Putin seems likely to expand it. 'Wait and see' is becoming increasingly untenable. Two main paradigms drive scientific worlds responses to the invasion:</p><p>One paradigm, followed by most of the Western world, is that the Russian invasion is a brutal unprovoked attack that must be punished; we should not associate with the attackers. Continuing scientific cooperation is 'business as usual,' tantamount to ignoring the invasion. <br /></p><p>The second paradigm is that international science is an important way to maintain lines of communication and cooperation. Maintaining scientific interchange is important for the scientists involved, and keeps the other side from being a nameless, faceless entity. In the long term, this might influence governments to be less antagonistic toward each other. </p><p>There are of course many slightly more nuanced approaches, mostly focused on punishing the relevant governments and government entities, while protecting the individual Russian and Belarusian scientists to the extent possible.</p><p>Both of these approaches have much merit, but they point in different directions. Different scientists and scientific organizations have emphasized these two paradigms differently. My personal view is that where they conflict, I will support the invadees over the invaders, and support the Ukrainian point of view, which is clearly that this is not a time for business as usual. This approach has limits - scientific contact during the cold war clearly had significant benefits for all, but the invasion of Ukraine seems closer to Hitler in 1938 than the cold war. <br /></p><p>Germany's <a href="https://fair-center.eu/" target="_blank">Facility for Antiproton and Ion Research (FAIR) </a>has <a href="https://fair-center.eu/ueber_uns/geschaeftsfuehrung/ma_versammlung/stellungnahme-zum-angriffskrieg-von-russland-auf-die-ukraine" target="_blank">condemned the invasion, and suspended all cooperation with Russian institutions,</a> even at a cost of a several year delay in their new accelerator. <a href="https://twiki.cern.ch/twiki/bin/view/CALICE/WebHome">The CALICE Collaboration</a> (a coalition that is developing new methods of calorimetry for high-energy physics experiments) has issued a similar condemnation, suspending Russian institutions from the Institution Board, prohibiting CALICE presentation by scientists from Russian institutions, and also banning CALICE presentations at conferences in Russia. </p><p>Other large projects have taken much less action. For example, the <a href="https://www.iter.org/" target="_blank">International Thermonuclear Experimental Reactor (ITER) </a>has not visibly reacted to the invasion. Similarly, U. S. Dept. of Energy laboratories have not said anything, although some experiments involving both Russian and European collaborators have had intense discussions about the way forward. </p><p>As noted below, CERN has taken a somewhat middle view, issuing a statement of solidarity with Ukraine, suspending much cooperation with Russia, and, although not expelling Russian scientists, stopping new collaboration with Russia. Further action may be taken at the next CERN Council meeting in June, possibly including expelling Russia. This would be a major shift for CERN, since it was founded to improve cooperation in Europe in the aftermath of World War II - exactly per the second thrust above.</p><p>None of these decisions deal explicitly with scientific authorship for work that is already complete, or largely complete. Scientific ethics rules require giving authorship credit to the people who did the work. These rules do not include exceptions for changing rules from funding agencies that require (in the case of Germany, Poland and Finland, at least) an immediate end to collaboration. </p><p>For now, the large CERN LHC collaborations are posting their papers on the <a href="https://arxiv.org/" target="_blank">Cornell arXiv</a>, authored by 'the XXX Collaboration', without individual names. This may buy time, but it is not a long-term solution, since author lists are required before the papers are published in scientific journals. Some papers from smaller collaborations have come out listing Russian authors, but without their Russian institutional affiliation. To me, this seems like the least bad solution to a very difficult solution - we properly recognize the work of our Russian colleagues, but avoid giving credit to the institutions that are on record as supporting the war. <br /></p><p><br /></p><p> </p><p><br /></p><p><br /></p><p> </p><p><br /></p><p><br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-12612905590124307932022-03-21T12:47:00.006-07:002022-03-21T12:47:58.833-07:00Science in the age of Ukraine: update<p> One additional item regarding Russian involvement in world science: According to <a href="https://twitter.com/RobynDixon__/status/1505964799825518595?cxt=HHwWhoC9nbXAoeYpAAAA">a tweet</a> by Robyn Dixon, the Moscow Bureau Chief of the Washington Post, Russia has now barred university staff from publishing in international (presumably non-Russian) scientific journals or attending international conferences. </p><p>If this is enforced, this will essentially bar all collaborative publications, since I can't imagine non-Russians being willing to publish in Russian journals. All of the LHC experiments (and many many other international collaborations) have a long pipeline of papers at various stages in the analyzing/writing/editing/publication process. What will happen to these papers? </p><p>There may be a precedent from the height of the cold war, when the West and the Soviet Union had parallel journal structures, and cross-publishing was uncommon. A. B. Migda published his' 1956 quantum mechanical calculation of Landau-Pomeranchuk-Migdal suppression of bremsstrahlung and pair production in both the American <a href="https://inspirehep.net/literature/2453">Physical Review </a>and the Soviet <a href="https://inspirehep.net/literature/41072">Doklady Akad Nauk SSR</a>. Now, the Physical Review article is well known and still heavily cited, while the Doklady Akad Nauk SSR article is mostly forgotten. </p><p>If all better solutions fall through, one could imagine a solution where the Russian part of a collaboration publishes a result in Russian journals, while the Western part publishes in a Western journal. I am sure that many readers will be slightly outraged by this idea. I do not claim that it is a good idea, but it may be the least-bad route forward if the Russian-Western estrangement drags on for longer than different collaboration can hold off on publications in the hope that the author list problem will resolve itself. <br /></p><p><br /></p><p><br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-1707613046194016052022-03-13T21:02:00.001-07:002022-03-13T21:02:43.584-07:00Science in the age of Ukraine<p>
</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEhuUzmQOfc3xbkFw-kKkWS8ngbVdC2W7CbNDF5bI0p-dxofTh2Py6i06tf82bmqNwqoacUCWRJjf6yAK85SZW8bO2v1f3s1Ol0alQ0x-w89DK6PqNtXJKgap8QaRcMKN3PfiJ5dhG374dDdUCfTxZer7OGfblJm1YeLSiqGfLwMnrEqOK4pXjsQbaLA=s285" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="189" data-original-width="285" height="189" src="https://blogger.googleusercontent.com/img/a/AVvXsEhuUzmQOfc3xbkFw-kKkWS8ngbVdC2W7CbNDF5bI0p-dxofTh2Py6i06tf82bmqNwqoacUCWRJjf6yAK85SZW8bO2v1f3s1Ol0alQ0x-w89DK6PqNtXJKgap8QaRcMKN3PfiJ5dhG374dDdUCfTxZer7OGfblJm1YeLSiqGfLwMnrEqOK4pXjsQbaLA" width="285" /></a></div><br /><p></p><p class="MsoNormal">Watching the news the past two weeks has been difficult –
the scenes from Ukraine are reminiscent of World War II, and the brutal unprovoked
invasion by Putin’s Russia has few parallels in more recent history. <span style="mso-spacerun: yes;"> </span>The one bright spot has been the U. S. and
international reaction, where a consensus in support of Ukraine has developed,
coupled with an active resupply of weapons and strong sanctions on Russia.<span style="mso-spacerun: yes;"> </span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">The Russian invasion also affect science.<span style="mso-spacerun: yes;"> </span>Science is international, and most large
collaborations include Russian and/or Ukrainian colleagues.<span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span>Naturally,
there has been much talk about if/how to sanction Russian scientists, with many groups favoring their immediate ouster. <span style="mso-spacerun: yes;"> </span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Many of these scientific collaborations are long-standing.<span style="mso-spacerun: yes;"> </span>The ALICE Collaboration (of which I am a
member) at CERN’s [in English: European Organization for Nuclear Research] Large
Hadron Collider has roots that go back more than 20 years, and much of the data
now being published was taken in the mid 2010’s, with significant Russian
involvement in both detector construction, data taking, and calibration and software.
<span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span>The
analysis connected with a single paper typically extends over more than a year,
and involves people from multiple institutions.<span style="mso-spacerun: yes;"> </span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">When a paper is written, there are clear standards for the
required level of involvement to merit authorship.<span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span>This
is true in both the broader scientific world, and, with more specific
standards, within ALICE and other large collaborations.<span style="mso-spacerun: yes;"> </span>Omitting
deserving contributor from the author list can be considered either
scientific misconduct (failing to give credit) or plagiarism (if the
contributed actually wrote some of the text).<span style="mso-spacerun: yes;"> </span>Per these rules, is unethical to rob Russian scientists of scientific credit for the work that they have done. <br /></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">But, people are rightly outraged by Russian behavior. Ukrainian
scientists very rightfully do not want to collaborate with Russian scientists,
and have called for Russia’s ouster from CERN.<span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;">Some</span> European funding
agencies have banned collaboration with Russian authors, including joint
publications.<span style="mso-spacerun: yes;"> <a href="https://www.science.org/content/article/few-journals-heed-calls-boycott-russian-papers">This extends to scientific journal operations</a>. <br /></span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">On the other hand, during the first ~ week of the war, before
it became illegal for them, many Russian scientists spoke out against the war. It
feels wrong to sanction <a href="https://docs.google.com/forms/d/e/1FAIpQLSd724tyPAFifsxHAjaoiWtlA0AwGlIKYOKHk4KMIKCQ67IKoA/viewform?dm_i=1ZJN,7ROH5,SJB7KV,VOJW5,1" target="_blank">people who spoke up, at some personal risk.</a><span style="mso-spacerun: yes;"><a href="https://docs.google.com/forms/d/e/1FAIpQLSd724tyPAFifsxHAjaoiWtlA0AwGlIKYOKHk4KMIKCQ67IKoA/viewform?dm_i=1ZJN,7ROH5,SJB7KV,VOJW5,1" target="_blank"> </a> </span>Now, the
scientists have been forced into silence, and their institutions are speaking
out in favor of the invasion. <span style="mso-spacerun: yes;"> </span>So, one
goal would be to sanction the institutes, but not individual scientists.<span style="mso-spacerun: yes;"> </span>This is unfortunately easier said than done.
</p><p class="MsoNormal"> <br /></p>
<p class="MsoNormal">Finding the right direction is not easy.<span style="mso-spacerun: yes;"> </span>CERN, and most other international organizations)
took no action during previous Russian invasions, such as Hungary in 1956, Czechoslovakia
in 1968, Afghanistan in 1979 or Crimea and Donbass in 2014. <a href="https://www.science.org/content/article/ukrainian-physicists-call-russia-s-ouster-cern">The CERN Council recently decided to suspend Russia’s status as an observer at CERN.</a> <span style="mso-spacerun: yes;"></span>They are not currently
ousting the Russian scientists who are already working at CERN, but are also
not expanding any ties.<span style="mso-spacerun: yes;"> </span>This was clearly
an attempt to find a middle ground, and it may be suitable short-term.<span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span>Other
organizations have taken a range of actions, ranging from nothing (at least so
far, such as <a href="https://www.livescience.com/russian-invasion-ukraine-imperils-science">International Thermonuclear Experimental Reactor (ITER)</a>) to suspending Russian membership (<a href="http://www.nupecc.org/" target="_blank">Nuclear Physics European CollaborationCommittee (NuPECC)</a>).<span style="mso-spacerun: yes;"> </span>And, many
institutions are taking steps to support their Ukrainian colleagues who have
been affected by the invasion. <br /></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Medium and long term, this solution is not enough, due to some nagging problems. One involves
publications.<span style="mso-spacerun: yes;"> </span>If Ukrainians and other
European scientists will not or cannot (due to funding restrictions) publish
with Russians, what do we do with ready-for-submission manuscripts with authors
from both groups?<span style="mso-spacerun: yes;"> </span>It seems wrong to
drop the Russian authors, and at least equally wrong to let the presence of
Russian authors keep other scientists from signing these papers.<span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span>So,
what to do?<span style="mso-spacerun: yes;"> </span>One possibility that has
been circulating would be to allow the Russian authors to sign the papers, but
as individuals, without their Russian institutional affiliations.<span style="mso-spacerun: yes;"> </span>Whether that will satisfy everyone remains to
be seen.<span style="mso-spacerun: yes;"> </span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Disclaimer:<span style="mso-spacerun: yes;"> </span>The opinions
expressed here are solely my own, and do not represent my employer or any other
institutions or collaborations.<span style="mso-spacerun: yes;"> </span></p><p class="MsoNormal"> </p>
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{page:WordSection1;}</style></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-59221064859283902742021-12-29T17:37:00.001-08:002021-12-29T17:37:18.476-08:00Do sterile neutrinos exist?<p>Sterile neutrinos are among the most intriguing BSM (beyond-standard-model) ideas around, with a long history of data hinting that something unusual is going on. The idea that neutrinos might oscillate into a new type of invisible (or nearly invisible) neutrinos has attracted much theoretical interest, along with a large number of experiments. Unfortunately, even after 25 years of study, we still don't know if sterile neutrinos exist or not.</p><p>The sterile neutrino story starts in the mid 1990s, when the <a href="https://en.wikipedia.org/wiki/Liquid_Scintillator_Neutrino_Detector" target="_blank">LSND (liquid Scintillator Neutrino Detector)</a> studied neutrinos produced by the decay-at-rest of pions from <a href="https://en.wikipedia.org/wiki/Los_Alamos_Neutron_Science_Center" target="_blank">LAMPF (the Los Alamos Meson Production Facility)</a>. <a href="https://arxiv.org/abs/nucl-ex/9709006">They observed a significant excess of electron-flavored neutrinos (henceforth electron-neutrinos) over the expectations.</a> The excess could naturally be explained via neutrino oscillations, but the oscillation parameters required to explain the data were inconsistent with the known neutrino masses and mixing. It could, however, be explained by positing a fourth neutrino flavor (beyond those connected with the electron, muon and tau leptons). These models are sometimes called 3+1 models, denoting three conventional neutrinos plus one sterile neutrino. <br /></p><p> The result was immediately controversial, even within the LSND collaboration. The concern was that there could be some type of unmodelled background, such as neutrons sneaking into the detector. The <a href="https://en.wikipedia.org/wiki/KARMEN" target="_blank">KARMEN experiment</a> at Rutherford Appleton Laboratory (in England) searched for similar oscillations, but <a href="https://arxiv.org/abs/hep-ex/9801007" target="_blank">did not find anything anomalous. </a><br /></p><p>LSND was followed by the MiniBoone experiment at Fermilab, which ran from 2002 to about 2008. MiniBoone was designed to confirm or refuse the LSND excess. Unfortunately, it also found <a href="https://arxiv.org/pdf/1303.2588" target="_blank">an anomalous result, but one which was in some tension with the LSND result</a>, at least within a 3+1 model.; their 2013 paper used the phrases 'have some overlap with' and 'marginally compatible.' This led to a profusion of more complex models, with a 3+2 model, with two sterile flavors gaining some popularity. Of course, one expects that a model with more free parameters to do a better job of fitting the data. Models with unstable (decaying) sterile neutrinos were also proposed. <br /></p><p>By now, a good number of experiments were in position to search for sterile neutrinos. Unfortunately, they found a wide spectrum of results, with some favoring sterile neutrinos, and some not. IceCube was in the latter category, <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.141801" target="_blank">reporting results consistent with the standard model. </a><br /></p><p>There were also dedicated experiments, most notably MicroBoone at Fermilab. MicroBoone is a liquid argon time projection chamber, a follow-on to MiniBoone. The collaboration recently released their results late this year, with <a href="https://news.fnal.gov/2021/10/microboone-experiments-first-results-show-no-hint-of-a-sterile-neutrino/">four analyses (of the same data) finding that their data was consistent with the standard model.</a> </p><p>Of course, many theorists have pointed out ways that the MicroBoone null results could be compatible with the previous LSND and MiniBoone positive results. So, we still don't really know if sterile neutrinos exist or not. However, MicroBoone is a strong experiment, designed to avoid MicroBoone's weak spots (e. g. the ability to distinguish photons and electrons). It did not, however, cover exactly the same range of parameters that MiniBoone did. It would be a bit of a coincidence that nature provided sterile neutrinos with the right characteristics to elude MicroBoone. So, although sterile neutrinos are not impossible, but they seem less likely than they did on New Years Day in 2021.<br /></p><p><br /></p><p><br /></p><p><br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-1094804320538592522021-11-01T16:41:00.001-07:002021-11-01T16:41:46.950-07:00Seeing antineutrinos in a new way - the Glashow resonance<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjNxSY2OUJc_tJHoWGvmx23jSsRfpM7Rjos0VIM_-YirTSfTPkADfvmsdxQrPlCs7t_xp5SVzpS2BcwP1sYhYELVX-0FulUw6oNcyzPXlw7uDPvl0qYSfLidgoC3l-UiddcejgHSgG4Mik/s945/Feynman.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="623" data-original-width="945" height="132" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjNxSY2OUJc_tJHoWGvmx23jSsRfpM7Rjos0VIM_-YirTSfTPkADfvmsdxQrPlCs7t_xp5SVzpS2BcwP1sYhYELVX-0FulUw6oNcyzPXlw7uDPvl0qYSfLidgoC3l-UiddcejgHSgG4Mik/w200-h132/Feynman.png" width="200" /></a></div> Recently, IceCube made its first definitive observation of an antineutrino, as it interacts with an atomic electron. The result was published in Nature, and is now available publicly on the <a href="https://arxiv.org/">arXiv preprint server</a>, as <a href="https://arxiv.org/abs/2110.15051">arXiv:2110.15051</a>. <br /><p></p><p>The reaction is very different from the usual <a href="https://en.wikipedia.org/wiki/Deep_inelastic_scattering">Deep Inelastic Scattering interactions</a>, where a neutrino or antineutrino interacts with an atomic nucleus. In this process, known as the<a href="https://en.wikipedia.org/wiki/Glashow_resonance"> Glashow Resonance,</a> an antineutrino and an electron annihilate each other, producing a W boson, as is shown in the diagram to the right The W boson is heavy (weighing about 85 times the mass of a proton), so it decays essentially immediately, usually into a quark and an
antiquark which then fragment producing two jets of particles. In IceCube, this leads to a cascade of particles, which looks like (nearly) a point source of light. For antineutrinos with the right energy (about 6.3 PeV), the interaction probability is very high - antineutrinos near the peak of the Glashow resonance only have a range in ice of about 100 km, only about 1% of the range for neutrinos of the same energy.<br /></p><p>This reaction is of great interest because it only happens with antineutrinos. Its not a big surprise that there are astrophysical antineutrinos, but it is nice to have clear confirmation. Later, with enough statistics (this will take a while), we can measure the neutrino:antineutrino ratio, which will tell us something about how the neutrinos are produced. </p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjUG32d8DSSwebfEefNOCKrdgeVPlwu2PotJMOUzvqvAXqxpst7V2zT48DTSiSb-5GAuGn3XcftkHT2kGbjgwh0ebHZcZYzM63E7vdcgFZOmupy63WilmnZ7pwm5A2-O0wzs_FZ2lXPU9A/s685/Glashow2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="555" data-original-width="685" height="518" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjUG32d8DSSwebfEefNOCKrdgeVPlwu2PotJMOUzvqvAXqxpst7V2zT48DTSiSb-5GAuGn3XcftkHT2kGbjgwh0ebHZcZYzM63E7vdcgFZOmupy63WilmnZ7pwm5A2-O0wzs_FZ2lXPU9A/w640-h518/Glashow2.png" width="640" /></a></div> <p></p><p>There were some interesting technical aspects of the event. The event display (above) shows a large cascade near the edge of the instrumented volume. In fact, the most likely location of the actual interaction is outside the detector, but close enough that we can reconstruct it well. However, closer examination shows some interesting features. </p><p>The bottom two parts of the graphic show the signals recorded in two of the optical modules, as a function of time. The blue curves show the expected light profile from a pure cascade at the reconstructed interaction point. The red curves show unexpected 'early' light. We believe that this light came from muons produced in the cascade. </p><p>The muons travelled at nearly the speed of light, while the light moves more slowly. This may sound surprising but in dense materials like ice, the light interacts with the medium (one way to think about is as if the light bounces around as it moves), and so only moves at about 3/4 of the speed of light. So, the muons will reach the vicinity of the optical sensors first, emitting early light which will reach the sensors before the light from the rest of the cascade. This early light signals the presence of muons, which show that the cascade was a hadronic shower, rather than purely electromagnetic. So, the cascade was not due to an electron-neutrino charged-current interaction. By eliminating the electron-neutrino hypothesis, we strengthen the case that this is indeed the Glashow resonance. Which, in turn, strengthens the case that we have observed an antineutrino. <br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-91906760512937597582021-08-09T14:47:00.004-07:002021-08-09T14:52:31.589-07:00Conferences - the International Cosmic Ray Conference<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjM9Fjp6x4IL9GhvAPu2dyhj1Dm27VTYIAiS8FGCMdNlRNIGfWmucv6V0fstI1nhMIcencpF_LPg0m_dYkWZ4TQ7ZPbJWaTwxRnhmlRUCuL-BG_hj8V0AZHfdw2i_y5jJdhD919N__oemM/s1140/header23-12.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="456" data-original-width="1140" height="134" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjM9Fjp6x4IL9GhvAPu2dyhj1Dm27VTYIAiS8FGCMdNlRNIGfWmucv6V0fstI1nhMIcencpF_LPg0m_dYkWZ4TQ7ZPbJWaTwxRnhmlRUCuL-BG_hj8V0AZHfdw2i_y5jJdhD919N__oemM/w336-h134/header23-12.jpg" width="336" /></a></div> <p></p><p>Last month, Berlin 'hosted' the <a href="https://icrc2021.desy.de/" target="_blank">37th International Cosmic Ray Conference (ICRC) </a>- the major conference for IceCube physics. It is a chance to meet, present new results and chat informally with colleagues from different experiments around the world - an important opportunity to exchange ideas, plan for future experiments, network, and, for the younger people, formally or informally job hunt.<br /></p><p>Unfortunately, Covid forced us into the virtual world. Although the organizers worked very hard and did a good job, it just isn't the same. Virtual meeting rooms may be getting better, but they're nowhere near in-person meetings, and the time differences limited the opportunity to interact.</p><p>The ICRC program included 693 talks and 687 posters, with 84 presentations from IceCube. To cope with the time differences, the talks were pre-recorded, viewable at leisure. Posters were also made available, accompanied by short 'flash' talks by the presenters. The organizers scheduled discussion sessions, clustering talks on similar topics. I found these were quite valuable, although there was so much to cover that some presentations did not get the attention than they deserved. </p><p>Although no major new results were presented (by IceCube or by other experiments), it was still a good opportunity to assess progress in the field. There was steady progress in most areas. IceCube presented a host of new searches for astrophysical neutrino searches, plus progress reports on a number of new studies of the diffuse (aggregate) neutrino flux, two measurements of the neutrino-nucleon cross-sections, and several contributions on neutrino oscillation studies. IceCube Gen2 also received some attention, with reports on the science case and hardware developments. The IceCube talks are linked to a<a href="https://arxiv.org/html/2107.06966" target="_blank"> master arXiv submission available here.</a><br /></p><p>One subfield with some nice developments is high-energy gamma-ray astronomy. The Chinese <a href="http://english.ihep.cas.cn/lhaaso/" target="_blank"><span>Large High Altitude Air Shower Observatory (LHAASO)</span></a> is now operational in Tibet. It features a large surface array consisting of water Cherenkov detectors to detect air shower particles that reach ground level, buried muon detectors to separate gamma-ray and hadronic showers, and Cherenkov telescopes for further gamma/hadron rejection. The large-area surface coverage and high-altitude site give it good acceptance for gamma-rays with energies down to 500 GeV. At TeV energies, it is the most sensitive observatory we have.<br /></p><p>Although it is still early days, LHAASO has presented observations of a twelve sources, including seeing photons with energies up to 1.4 PeV. One has to be careful about claims of maximum photon energies, but the events look good, and this is a considerable step up from previous maximum energies. At least most of the sources are likely to be in our galaxy. This is expected since photons with energies above about 50 TeV are attenuated in-flight, through interaction with lower-energy photons from the cosmic microwave background radiation. Even within our galaxy, only about 1/3 of the most energetic photons survive the trip to Earth. <br /></p><p><span></span></p><p><br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-30246540065504520522021-05-13T14:04:00.002-07:002021-05-13T14:04:34.835-07:00Happy Birthday to IceCube<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjjzccdh29ubX8ScCCPiJ3Wewm6NPuj2NND8ZDMIjsnqUZnIHAz9pcv7gBu8Wb8Hi7nRsDevgN1DoEF6pCOiZ5HU7nVJRAOx2DDQjQBH_IaFENwwa-VP9DQeATKQecgIayxqGA0wC91QKI/s1921/Birthday.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1921" data-original-width="1697" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjjzccdh29ubX8ScCCPiJ3Wewm6NPuj2NND8ZDMIjsnqUZnIHAz9pcv7gBu8Wb8Hi7nRsDevgN1DoEF6pCOiZ5HU7nVJRAOx2DDQjQBH_IaFENwwa-VP9DQeATKQecgIayxqGA0wC91QKI/s320/Birthday.jpg" /></a></div> IceCube turned 10 years old today! <p></p><p>Of course, there many way to determine IceCube' birth date. The one that we are choosing to celebrate is the 10th anniversary of the start of the first production data run using all 86 strings. We could also have celebrated the end of deployment of the 86 strings, which happened on December 17, 2020. But, the May date was more convenient; pre-Covid, we had intended to schedule our collaboration meeting around it, and also have a celebratory 'What have we learned' workshop. Alas, the in-person celebration and workshop will have to wait until we can safely travel again.<br /></p><p>For those who are interested, many IceCube institutions issued press releases and features. The <a href="https://newscenter.lbl.gov/2021/05/13/icecubes-decade-of-discovery/">LBNL story is available here</a>, while the <a href="https://icecube.wisc.edu/news/collaboration/2021/05/celebrating-icecubes-first-decade-of-discovery/">UW Madison release is available here.</a><br /></p><p>Here's to another 10 years, including the IceCube Upgrade and Generation 2! Minus the adolescent angst, of course.<br /><br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-5489616071537163742021-02-23T22:24:00.003-08:002021-02-23T22:24:44.856-08:00Here today, gone tomorrow: searching for transient sources in astrophysics<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKa6eufgXHAzWw2EYfl3OYGIrK8nqpBPR44WAOpVIwc4bTtzdEt84xSxDVer3dd1Mr7FWejl2feErEEwx1mRYzLYnlSQMgLc0DIwm7nFLBuAfCBM7NsP2sSsdpRGd6ZNqYGcZ0AXw7LG4/s1479/3C279.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="955" data-original-width="1479" height="259" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKa6eufgXHAzWw2EYfl3OYGIrK8nqpBPR44WAOpVIwc4bTtzdEt84xSxDVer3dd1Mr7FWejl2feErEEwx1mRYzLYnlSQMgLc0DIwm7nFLBuAfCBM7NsP2sSsdpRGd6ZNqYGcZ0AXw7LG4/w400-h259/3C279.png" width="400" /></a></div><br /><br /><p></p><p>Coming from a particle/nuclear physics background, when I started working on IceCube one of the bigger mental adjustments I had to make was to get used to the idea of transient sources. When an accelerator is running, its particle output is more-or-less constant. Not so with astrophysical objects. Many (not all) of the most interesting astrophysical objects vary considerably in output (by a factor of 10 or more), over different time scales. Depending on the source, periods of increased emission may or may not repeat, on either regular or irregular time scales. <br /></p><p>In fact, IceCube's most statistically significant signal, from the source TXS0506 was based partly on a search for transients, where we found a transient lasting about 7 months, as <a href="https://www.blogger.com/blog/post/edit/8058556114838797093/353352018444103553">I discussed in a previous post.</a> Transients can come over a wide range of length scales, from millisecond long bursts of radio waves called <a href="https://en.wikipedia.org/wiki/Fast_radio_burst">Fast Radio Bursts</a>, up to sources that probably change on time scales longer than we have been observing them. </p><p>In IceCube, time-varying sources add additional complexity to source searches, since searching over a wide range of time scales, degrees of repeatability, etc. can lead to a large increase in the number of trial factors: the more ways you slice and dice the data, the more likely you are to get a statistically significant result. It is critical to keep track of the number of different observations (positions in the sky, possible pulse start times and lengths etc.) to know if an observation is really statistically significant. For some sources, we can use radio, optical or X-rays to tell us the best places to look, reducing the number of trials factors</p><p>IceCube has recently released <a href="https://arxiv.org/pdf/2012.01079">a paper on a search for time-varying sources</a>. The paper included two types of searches. The first was an all-sky search that looked for emission on different time scales, from about 1/10 second to 100 days. This suffered from a large trials factor, for the reasons noted above. </p><p>The second search examined one object of particular interest: 3C279, which is a quasi-stellar object. Despite the 'quasi-stellar' name, it is a distant galaxy containing a massive black hole which powers the emission of powerful particle jets, which were recently imaged by the Event Horizon Telescope - the image above is from <a href="https://eventhorizontelescope.org/blog/something-is-lurking-in-the-heart-of-quasar-3c-279">their web page.</a> 3C279 is known to exhibit strong variability in radio, optical and X-ray emission. These factors made it an attractive place to search for neutrino emission, despite the long distance (5 billion light years). We used gamma-ray data (using photons with energies above 100 MeV) from the Fermi telescope to select time periods when 3C279 was particularly active. By focusing on the active periods from a single source, we were able to make a much more sensitive search. <br /></p><p>Unfortunately, we did not find anything using either approach. We are, however, reducing the
number of ways that Nature can hide the cosmic-ray accelerators that we
know must exist. We use the non-detection of neutrinos to put limits on how 3C279 could work as an accelerator. <br /></p><p><br /></p><p><br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-58393310414450843152021-01-13T15:39:00.000-08:002021-01-13T15:39:09.494-08:00IceCube has won the American Astronomical Society's Bruno Rossi Prize<p> </p><p> </p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh63Pfr8tCzDIWnTnxIpgseYud6lUZIXaf4qaba5_DCtRIm9je4OzSi_Gab2xTV6ZgVRbLsv9FAtqb2jsXjPFWcJMcr7hH4GR3o3r7fmL4wE8AaVNUbBPEZgjz32157pLROwwgbhdmNA28/s903/Rossi.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="779" data-original-width="903" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh63Pfr8tCzDIWnTnxIpgseYud6lUZIXaf4qaba5_DCtRIm9je4OzSi_Gab2xTV6ZgVRbLsv9FAtqb2jsXjPFWcJMcr7hH4GR3o3r7fmL4wE8AaVNUbBPEZgjz32157pLROwwgbhdmNA28/s320/Rossi.jpg" width="320" /></a></div><br />The American Astronomical
Society has awarded the 2021 Bruno Rossi Prize to Francis Halzen and
the IceCube Collaboration "for the discovery of a high-energy neutrino
flux of astrophysical origin." <p></p><p>We are very proud of this
award, which reflects on both the construction of IceCube and on the
data analysis (plus help from Mother Nature, for making the flux large
enough to be detectable). The announcement is posted at
<br />
<br /><a class="moz-txt-link-freetext" href="https://head.aas.org/rossi/rossi.recip.html#2021_ic">https://head.aas.org/rossi/rossi.recip.html#2021_ic</a>
<br />
<br />and there is an IceCube press release at
<br />
<br /></p><div style="text-align: left;"><a class="moz-txt-link-freetext" href="https://icecube.wisc.edu/news/view/799">https://icecube.wisc.edu/news/view/799</a></div><div style="text-align: left;"> </div><div style="text-align: left;">The prize is named after the Italian physicist Bruno Rossi,who was one of the pioneers of cosmic-ray physics. He won the 1954 Nobel Prize in Physics for the invention of coincidence circuits, which he used to show that large groups of cosmic-ray particles reached the ground simultaneously, i. e. that very high-energy cosmic-rays produce air showers consisting of large numbers of particles. <br /></div><p>
<br /><br />
</p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com1tag:blogger.com,1999:blog-8058556114838797093.post-49034892858720372352020-11-29T21:17:00.005-08:002020-11-29T21:17:53.134-08:00The curious case of the softening spectrum: more on astrophysical neutrinos<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEikXFbF-X_bPjCAcEWvikisuxGugBhJvt2wCuMIPC38H3sKBCjHUFgRbfkaiN25rScNV7gR2TJKEL9cnMC4ydgvYyM1T-1jy_EIcyb7MtJm3oS6iGgfAiIdQp_uUFnMY5Es0hOJzFN2Ups/s2048/Skymap.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1272" data-original-width="2048" height="249" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEikXFbF-X_bPjCAcEWvikisuxGugBhJvt2wCuMIPC38H3sKBCjHUFgRbfkaiN25rScNV7gR2TJKEL9cnMC4ydgvYyM1T-1jy_EIcyb7MtJm3oS6iGgfAiIdQp_uUFnMY5Es0hOJzFN2Ups/w400-h249/Skymap.png" width="400" /></a></div>IceCube has posted a set of papers on the arXiv, giving new results on starting events: neutrino interactions that occur within IceCube. These analyses use 102 events observed in 7 1/2 years of data,. There are many new results, including new measurements of the astrophysical neutrino flux and energy spectrum, evidence for the observation of tau neutrinos and the first measurement of the neutrino-nucleon cross-section using starting events. The papers are available on the arXiv preprint server, and have been submitted for journal publication:<p></p><p>"The IceCube high-energy starting event sample: Description and flux characterization with 7.5 years of data," R. Abbasi et al., available as <a href="https://arxiv.org/abs/2011.03545" target="_blank">arXiv:2011.03545.</a></p><p>"Measurement of Astrophysical tau neutrinos in IceCube's high-energy starting events, R. Abbasi et al., available as <a href="https://arxiv.org/abs/2011.03561" target="_blank">arXiv:2011.03561</a>.</p><p>"Measurement of the high-energy all-flavor neutrino-nucleon cross section with IceCube, R. Abbasi et al., available as <a href="https://arxiv.org/abs/2011.03560" target="_blank">arXiv:2011.03560</a>. </p><p>There were a couple of reasons to have three publications. These are three very different topics, based on rather different analysis techniques. But, length was also an issue: the first paper comes in at 51 pages, definitely on the long end of the spectrum for physics papers. This post will focus on the first paper, which also describes the data sample. <br /></p><p>The analyses in the first paper are very similar to those in previously published starting event analyses, which I discussed <a href="https://antarcticaneutrinos.blogspot.com/2013/11/evidence-for-high-energy-extra.html">here</a>. The current analyses benefits from more data, and better detector calibrations and better analysis software, giving better measurements of the energy deposited in the detector, better measurements of the neutrino directions, etc.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9ipAme2hXP5mBoXOhui2HQcqRGXDLXtwp5cPWOr2VY5rrsVu4FSnJlyBT_aPoPZuBcZOCmLJLBK3Eo-p8FgEgjCx48lS5cDy7LKzRV6nMkrGgK37_yCH5MFmhTHtXt5NrmBoKFLhD2x8/s2588/HESE7.5.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="878" data-original-width="2588" height="218" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9ipAme2hXP5mBoXOhui2HQcqRGXDLXtwp5cPWOr2VY5rrsVu4FSnJlyBT_aPoPZuBcZOCmLJLBK3Eo-p8FgEgjCx48lS5cDy7LKzRV6nMkrGgK37_yCH5MFmhTHtXt5NrmBoKFLhD2x8/w640-h218/HESE7.5.png" width="640" /></a></div><p></p><p>That said, the results have changed more than we would have expected. Most notably, the measured neutrino energy spectrum has gotten softer (i. e. there are fewer very energy astrophysical neutrinos, and more with lower energy). The figure immediately above shows the energy spectrum (expressed as energy deposited in the detector) and the zenith angle (where cos(theta)=+1 is going vertically downward, and cos(theta)=-1 is going vertically upward), compared to the expectations for atmosphe ric muons, atmospheric neutrinos (labelled as Atmo Conv.) and a fit to the astrophysical spectrum. The fit found the astrophysical spectrum was consistent with a flux phi=phi_0 (E_neutrino/100 TeV)^-alpha, where alpha=2.87+/-0.20. Here, phi_0 is a normalization constant. In comparison, previous contained event analyses found alpha in the 2.3 to 2.6 range, depending on which years of data were studied. The collaboration spent much time trying to determine what has changed. Otherwise, this paper would have been out some time ago. </p><p>We looked at every plausible explanation that we could find, and even some that were clearly less plausible. If we use just the first 4 years of data, the results were similar to those in the previous analysis. If we swap the old and new software and calibration, very little changes. There is no evidence for any change in the detector behavior; one expects detectors buried under a mile of ice and held under constant conditions to be very stable, and, as expected, we see no significant changes in atmospheric neutrinos, cosmic-ray muons, or any other measure of detector performance. The interactions were spread pretty evenly throughout the detector, so it is not a problem in a small part of the detector. The astrophysical neutrinos come from a large number (very likely >50) source from many directions in the sky, so it is not plausible that this is due to a change in their source. So, in the end, I am just chalking this up to statistics - once in a while, we expect large (roughly 2 sigma) statistical fluctuations, and this seems to be one of those occasions.</p><p> The neutrino arrival directions have also changed somewhat. This is better understood, and comes from a combination of improved analysis techniques and a better understanding of how light scatters and is absorbed in the Antarctic ice. For each neutrino candidate, we estimate the probability of it coming from any given direction in the sky. The result is a blob (which may be regular or irregular, depending on the reconstruction) centered around the most likely arrival direction. The graphic at the top shows our revised sky map, which shows the estimated flux coming from different directions, where we add up the probability that each neutrino came from a given direction. The gray dot shows the center of our galaxy, and the gray curve shows the galactic plane. <br /></p><p>The color code gives the "Test statistic," a measure of how likely the measured flux from that direction can be explained by background. There is a hot spot (every map must have a hottest spot), but it is not statistically significant; this map shows no evidence for any specific neutrino sources. It should be noted that, because we have only a handful of contained events, this search is less sensitive than studies using through-going muons.<br /></p><p><br /></p><p><br /></p><p><span class="__ListItemAction__"><span class="__IconText__"></span></span></p><p><span class="__ListItemAction__"><span class="__IconText__"></span></span></p><p><span class="__ListItemAction__"><a href="https://inspirehep.net/literature?q=refersto:recid:1828957"><span class="__IconText__"><span class="v-top"></span></span></a></span></p><p> <br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com1tag:blogger.com,1999:blog-8058556114838797093.post-20472546695252759982020-11-10T17:18:00.005-08:002020-11-10T17:18:39.121-08:00Science in the age of Covid<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhXpUKrdk9qqvZY13tJ9ikPZf_PrOqV67E4mPTS1p0ui2gzM5YwVfveeFdsTsoxFeEB3enLz7IvyDFVTTUcbifKiKwm35aSVIoCHy-YNKxPj21FK3aO8yNZIkGblSR-pzXKrI12lLcDuAk/s2048/Basler.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1536" data-original-width="2048" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhXpUKrdk9qqvZY13tJ9ikPZf_PrOqV67E4mPTS1p0ui2gzM5YwVfveeFdsTsoxFeEB3enLz7IvyDFVTTUcbifKiKwm35aSVIoCHy-YNKxPj21FK3aO8yNZIkGblSR-pzXKrI12lLcDuAk/s320/Basler.jpg" width="320" /></a></div> Hi,<p></p><p>Apologies because I have not updated this blog in quite a while. I'm healthy, but Covid has brought many changes to my work life, and almost everything takes longer. </p><p>Covid has had an enormous effect on scientists, and a somewhat lesser but still very sizable effect on science. I am one of the fairly large fraction of physicists who mostly work on a computer. So, I am able to work at home, and I do so. There is a significant hit to productivity because I can no longer walk next door and talk to my colleagues - everything requires an appointment and a zoom call. </p><p>Laboratory science has taken a much larger hit. Lawrence Berkeley Lab, like most other research institutions, was almost entirely shut down for about six months, so all laboratory work stopped. Now, we are slowly and carefully ramping up lab work, with a whole host of anti-Covid precautions, about physical separation, etc. Of course, Covid-related work has become very high priority. At LBNL, this includes using the <a href="als.lbl.gov">Advanced Light Source</a> (it produces intense beams of X-rays) to study the structure of important proteins, using the <a href="www.nersc.gov" target="_blank">NERSC</a> supercomputers to study protein-Covid interactions, and, of course, much biological research. <br /></p><p>Polar science has been affected even more. There is a strong determination to keep Covid out of Antarctica. To do so, the U. S. polar program has slashed the number of people who are going there this coming Astral summer. The only activities that are supported are those that keep the U. S. stations running, and prevent damage to scientific infrastructure. For IceCube, we will be able to swap winter-overs as the Pole, but not much more. The usual transportation, using Air Force and NY Air National Guard LC-130 transports will not occur; instead there will be a small number of flights on Baslers (shown above, they are much upgraded DC-3s with turboprop engines), with very limited passenger space, and even more limited cargo transport. </p><p>Everyone going to Antarctica will spend time quarantining in both the U. S. and New Zealand. Even this has been tough - New Zealand is essentially closed to visitors, so special arrangements were required to allow polar program personnel in. Fortunately, IceCube is running well, so the main effect is to put off some planned software upgrades, plus the surface deployment of new prototype air shower detectors. </p><p>For younger scientists without career positions,, the effects of Covid are especially drastic. Colleges and universities are in dire straits financially, and have consequently cut faculty hiring. One estimate I saw was that the number of advertised faculty positions is down by 70%. This is a huge cut, especially for people who were positioning themselves to apply for jobs this year. The situation in industry is better, but it is still not as good as last year. Overall, physicists are probably no worse off than most other professions, but young people have a limited time window to apply for faculty positions, and budget limitations will create a squeeze that will likely last for several years. <br /></p><p><br /></p><p><br /></p>Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-69879987914887168172019-05-12T17:40:00.001-07:002019-05-12T17:44:18.149-07:00Here comes the tau?<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhOyCLMouWU-RavQMF39FVv324I3eB9zyTD-qtkS7tdO0oQDH1HaOUdTv9kcTGX654xl6EVKWxxs8zmVoGEjhb0FzkqLwh_5Bto88bq_E9M2Eu1uIjjqi4RS05YciO17mKL7_5MFBYZBfw/s1600/separated_double_bang.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="656" data-original-width="1012" height="207" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhOyCLMouWU-RavQMF39FVv324I3eB9zyTD-qtkS7tdO0oQDH1HaOUdTv9kcTGX654xl6EVKWxxs8zmVoGEjhb0FzkqLwh_5Bto88bq_E9M2Eu1uIjjqi4RS05YciO17mKL7_5MFBYZBfw/s320/separated_double_bang.png" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Simulated tau neutrino event in IceCube. Each sphere is an optical module that observed light, with the size scaling with the number of photons. The color indicates the timing of the light, from red (earliest) to blue (latest).</td></tr>
</tbody></table>
One of the more interesting/embarrassing holes in IceCube's physics portfolio was the tau neutrino. Neutrinos come in three flavors: electron, muon and tau, each tied to the charged lepton of the same name. Over long distances, these neutrinos can oscillate, changing flavors. So, no matter what flavor ratio a neutrino beam is produced with, over long distances, we expect it to oscillate and reach Earth as a roughly 1:1:1 ratio of electron:muon:tau neutrinos.<br />
<br />
Since very few tau neutrinos are produced directly on Earth, the observation of tau neutrinos was considered to be a clear sign of astrophysical neutrinos, and many many papers discussed the signatures and expectations. <a href="https://www.sciencedirect.com/science/article/pii/0927650594000433?via%3Dihub">A beautiful 1995 paper by John Learned and Sandip Pakvasa</a> (<a href="https://arxiv.org/abs/hep-ph/9405296">also available on the arXiv</a> - soon after it was founded) pointed out that sufficiently energetic tau neutrinos could produce a distinctive 'double bang' signature - a large cascade when the neutrino interacted, and a second when the resulting tau lepton decays. Even though the tau lepton lifetime is very small (3*10<sup>-13</sup> s), when it has energies of a PeV (10<sup>15</sup> eV) or higher, a Lorentz boost extends its lifetime in the Earth frame of reference so that the two bangs can be separated by an average of (Energy/1 PeV) * 50 meters, making for a distinctive signature seen in the simulation shown above, with two distinctive light clusters. Unfortunately, IceCube has not seen this signature, and we have also not seen enough PeV-energy neutrinos so that we can expect to see it. <br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRuU5hz2tmb3cQnYxFG62XjZQhEtIypoLEqpcTjQeCFe5Bu03KGkPxa96ZT-PhOAbpy7x31JogEj-_zJZtmp0uRsIRofr1PdGT9XbYIs1guBQSOSVX3Z-NYjI8gUispfS9MY8pyBaiNXU/s1600/taucandidate.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1237" data-original-width="1600" height="308" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRuU5hz2tmb3cQnYxFG62XjZQhEtIypoLEqpcTjQeCFe5Bu03KGkPxa96ZT-PhOAbpy7x31JogEj-_zJZtmp0uRsIRofr1PdGT9XbYIs1guBQSOSVX3Z-NYjI8gUispfS9MY8pyBaiNXU/s400/taucandidate.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">A candidate tau neutrino event seen in IceCube. Each sphere is an optical module that observed light, with the size
scaling with the number of photons. The color indicates the timing of
the light, from red (earliest) to blue (latest). The seven plots show the waveforms (light vs. time) for certain optical modules; several show apparent double-pulse signatures. </td></tr>
</tbody></table>
<br />
However, IceCube is developing techniques that will allow us to see tau neutrinos with lower energies, where the two bangs are closer together. Even if they are so close together (10-30 m) that we cannot separate the overall light clouds, there may be some optical modules that see pulses from the two cascades at separate times, producing a double-pulse topology in an individual optical module. The figure above shows one candidate event, along with waveforms from some of the modules, showing the double-pulse signature. A word of caution is in order - there are some possible background processes that could mimic these signatures - but this is considered by IceCube to be evidence for tau neutrinos. "Evidence" typically means that the statistical significance is 3 sigma or more, not the 5 sigma required to claim a detection. Since we expect to see tau neutrinos, this is reasonably convincing, an it seems safe to say that the holes has largely been filled in. We look forward to more precise measurements, of course, to check in more detail for consistency with the standard acceleration scenarios. <br />
<br />
The tau neutrino work has been presented in several recent conference presentations, including ones with writeups by <a href="https://scipost.org/10.21468/SciPostPhysProc.1.030">Daan van Eijk</a> and <a href="https://pos.sissa.it/301/1009">Logan Wille </a>and <a href="https://arxiv.org/pdf/1905.04237">Juliana Stachurska</a>.<br />
<br />Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0tag:blogger.com,1999:blog-8058556114838797093.post-9517835414525269202018-09-17T15:50:00.004-07:002018-09-17T15:53:16.204-07:00More neutrino interaction physics with IceCubeOnce again, IceCube has shown that we can study high-energy neutrinos in their own right, rather than just as astrophysical probes. This analysis used a sample of starting tracks in 5 years of data, from neutrinos that interacted within the detector, producing a hadronic cascade from the nuclear target recoil, and a muon from the lepton, in a reaction written as neutrino + nucleon (proton or neutron) -> muon + X, where X is the shower of particles produced by the recoiling nucleon. In these interactions, there are two quantities to measure, the energy of the muon, and the energy of the shower. The inelasticity is the energy of the cascade divided by the total energy (the sum of the shower and muon energy). The distribution of inelasticity is well predicted by the Standard Model of Particle Physics, but has not been measured at energies above 500 GeV (5*10^11 electron volts). With IceCube, we have extended the measurement to energies above 100 TeV (10^14 electron volts) - a factor of 200 upward in energy. This plot shows the measured average inelasticity, from our new Icecube preprint, available <a href="https://arxiv.org/abs/1809.04150" target="_blank">here</a>, or directly as <a href="https://arxiv.org/pdf/1809.04150" target="_blank">pdf</a>. <br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRgjeuv0wqxZtMI_RLm5Xcfnw4lCuEKa_DHN6ftLl5-Op_GXx_-gFvdOBQ9hb3rvTmefbifTHbrgCb00bEbvqusWUjbSkxksTg5g6mfsLPKeH01mGF7z6UdL-eBGTlUpZfX-CdoZhhJYc/s1600/split_fit_inel.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1200" data-original-width="1600" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRgjeuv0wqxZtMI_RLm5Xcfnw4lCuEKa_DHN6ftLl5-Op_GXx_-gFvdOBQ9hb3rvTmefbifTHbrgCb00bEbvqusWUjbSkxksTg5g6mfsLPKeH01mGF7z6UdL-eBGTlUpZfX-CdoZhhJYc/s400/split_fit_inel.jpg" width="400" /></a></div>
The points show the inelasticity, while the blue and green curves show the standard model predictions for neutrinos and antineutrinos respectively. The red curve shows the expectation for the mixture expected in IceCube. For aficionados, this calculation is done at next-to-leading order accuracy, with BFKL evolution to low-x partons.<br />
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This measurement is sensitive both to potential beyond-standard-model physics, which would likely have a rather different inelasticity distribution than for the expected interactions. Even the standard model cross-section is sensitive to the number of low-momentum quarks and antiquarks in the target nucleus.<br />
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Inelasticity is interesting in it's own right. But, the inelasticity can also be used to probe a number of additional physics topics. Neutrinos and antineutrinos have different inelasticity distributions, so by assuming the standard model values, we can measure the neutrino:antineutrino ratio. As can be inferred from the plot above, it is exactly as expected. Unfortunately, at the energies where IceCube is sensitive, we are mostly studying atmospheric neutrinos, not astrophysical.<br />
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We can also use inelasticity to probe astrophysical neutrinos. Although the neutrinos selected here are mostly muon neutrinos, some tau neutrinos make it into the fit, and it is possible to use similar criteria to select a matching set of cascades. The plot below shows the flavor triangle found from this study.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgULN0KgI82Vmh0VE7k5e6BsCmjdsCSGqZBxMoiB2PXOxOQv9ZAPsKjJeJJIy7P16-NqkZkAOvGE16eN3zaYm8vebxr3mieAx_pz6WZL62WfDpMZrJJ1-GK9g3paGD6rhNBBYRad7c26aw/s1600/flav_scan.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1200" data-original-width="1600" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgULN0KgI82Vmh0VE7k5e6BsCmjdsCSGqZBxMoiB2PXOxOQv9ZAPsKjJeJJIy7P16-NqkZkAOvGE16eN3zaYm8vebxr3mieAx_pz6WZL62WfDpMZrJJ1-GK9g3paGD6rhNBBYRad7c26aw/s400/flav_scan.jpg" width="400" /></a></div>
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Each point on the flavor triangle corresponds to a unique mixture of electron, muon and tau neutrinos. The upper point is all muon neutrino, with the lower left and lower-right points corresponding to all tau neutrinos and all electron neutrinos respectively. The colors show the relatively likelihood, with the best-fit point (cross) corresponding to 83% tau neutrino, 17% electron neutrino and no muon neutrino. Unfortunately, the errors are large, so none of the different standard acceleration scenarios can be ruled out.<br />
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This work was done by my student, Gary Binder. Besides the IceCube paper, he wrote a very nice <a href="https://docushare.icecube.wisc.edu/dsweb/Get/Document-82240/thesis.pdf" target="_blank">dissertation, available here</a>. For this work, he won the <a href="https://www.globalneutrinonetwork.org/" target="_blank">GNN (Global Neutrino Network)</a> <a href="https://www.globalneutrinonetwork.org/e227565/" target="_blank">dissertation prize for 2018</a>. <br />
<br />Unknownhttp://www.blogger.com/profile/08787316990900279114noreply@blogger.com0