ARIANNA 2010: The Journey to Moore's Bay

I have been remiss about posting about ARIANNA, in particular on the 2010/11 field season. UC Irvine Prof. Steve Barwick and graduate student Jordan Hanson travelled back to the site in December, 2009. Jordan sent me some pictures and text describing that trip. Because of the length, it is divided into four posts. Here is part 1 of Jordans account:

The Journey to Moore's Bay, 2010

My name is Jordan Hanson, and I am a graduate student researcher at UC Irvine working for the ARIANNA collaboration. My research focuses on the viability of ARIANNA to detect high energy neutrinos in the background-free environment of Moore's Bay, in Western Antarctica. My adviser, Steve Barwick, and I, travelled to Antarctica in the winter of 2010 to revive the prototype station and make measurements of the properties of the ice beneath it.

Every long journey begins with a first step. Ours was to travel to Christchurch, New Zealand, which is the gateway city that coordinates flights to McMurdo Station, located on Ross Island in the middle of the Ross Ice Shelf. Christchurch hosts the United States Antarctic Program (USAP) and the clothing distribution center (CDC). Upon our arrival, Steve and I met with USAP personnel to gather our extreme cold weather (ECW) gear, necessary for landing on an ice shelf at almost 80 degrees South latitude. While staying at the Windsor Bed and Breakfast in Christchurch, we encountered other scientists traveling to the Antarctic continent to perform the season's research. There were geologists, climatologists, astronomers, and physicists like us. We even met several scientists in our field of high energy neutrino astronomy, working for the IceCube project (see recent posts on this blog). Specifically, we met a team led by Per-Olof Hulth, of the University of Stockholm. I had an interesting conversation with Reina Maruyama about DM-Ice, a project related to IceCube focusing on direct detection of dark matter.

On the morning of our departure, we had coffee with Vladimir Papitashvili, the director of the Aeronomy and Astrophysical Sciences Program (Office of Polar Programs) at the National Science Foundation. I learned about many other experiments like ours taking place around the Antarctic continent. When it was time to leave, we all boarded the bus to the C-17 and were escorted onto the aircraft by military personnel.

Although the details of McMurdo station and how it operates have been covered in previous posts, I'll recount our experiences briefly. We landed on the Ross Ice Shelf, near the southern tip of Ross Island, where there is a station called McMurdo station. In the summer months, it is home to over a thousand individuals, and it forms a scientific community complete with technical and logistical support staff. The dedication and hard work of these support staffs cannot be understated. Specifically, Steve and I worked with Jessy Jenkins, our point of contact, whose job it was to coordinate the accumulation of survival gear, our technical equipment, food and supplies, fuel, and helicopters necessary for accomplishing our mission. Rebekah Davis travelled with us initially to the field, to manage our camp and assist with things like tent building and radio communications. After assembling our gear and coordinating with helo-ops, we were ready to launch into the wilderness. We were accompanied by wireless communications technicians, led by Bill Nesbit, whose goal it was to establish wireless internet at the site of our prototype station.

We're done - IceCube is finished

After 7 construction seasons, IceCube is finally complete!

Construction ended quietly on Saturday, Dec. 18th(New Zealand date), as the last string was lowered into the ice, completing the 86-string, 5,160 optical module array. This was the last of 7 strings deployed in December; this was a very short season compared with the last two seasons, when 19 and 20 strings were deployed, respectively. Work at the Pole has now turned toward packing up the drill for long-term storage, upgrading the computer system on the surface, and sending now-surplus material North.

The occassion was celebrated by press-releases galore:

Several groups have issued press releases to note the occasion:

From the NSF and University of Wisconsin:

http://www.nsf.gov/news/news_summ.jsp?cntn_id=118236&org=NSF&from=news

From LBNL:

http://www.physorg.com/news/2010-12-icecube-world-largest-neutrino-observatory.html

From DESY (in German):

http://www.desy.de/e428/e548/e4802/e87334/e105250/index_ger.html

There was also a modicum of press coverage - check out google or google news for the latest.

A belated Happy Holidays to everyone.

The Coming Antarctic Season

Preparation for the coming Antarctic field season are in full swing, in both IceCube and ARIANNA.

On ARIANNA, Steve Barwick and Jordan Hanson visited LBNL last week, to learn about the station hardware and software. They will be going out to Moore's Bay in early December, to recondition the station, and perform a number of calibration measurements. These calibrations should allow us to set a limit on the flux of ultra-high energy neutrinos. Although the limit from one station will not be very stringent, carrying out the analysis through to the end is a good way to convince ourselves (and peer reviewers) that we understand the system thoroughly.

Unfortunately, even though the sun is now above the horizon 24 hours/day, the station has not yet 'woken up' from the Antarctic winter hiatus. The most likely possibility (also the most optimistic) is that the battery cracked during the winter. There are some good reasons to believe this - the charge controller left it in a discharged state, and batteries are known to be a problem at low temperatures. Alternately, maybe the solar panels are still coated with snow, or, more likely, the Iridium antenna or some other part broke. The worst case scenario would be if the station failed mechanically, and that the solar panels, etc. will be strewn across the Ice Shelf, buried under a winters accumulation of snow.

The first IceCube personnel are already in New Zealand, waiting for flights to McMurdo station. The plan for IceCube is to drill the final seven holes and deploy strings in them, and then prepare the drilling system for hibernation. In addition, two of the strings will include sodium-iodide crystals which will be used to look for dark matter. Although the IceCube project included funding to disassemble the drilling system and move it North (to avoid leaving any junk in Antarctica), the drill has many future applications. In particular, if the dark matter prototype works well, then additional crystals may be deployed, in special background-free pressure vessels.

Public Lecture

I gave a public "Sciece@Cal" lecture last Saturday, on "Neutrino Astronomy in Antarctica. I talked about why we want to do neutrino astronomy, and about IceCube and ARIANNA.

Science@Cal is a monthly series of Saturday lectures, intended for anybody who is interested, on various subjects. It was an interesting experience, attracting attendees with a wide range of backgrounds, and, clearly, based on the questions, a wide range of background knowledge.

A video of the talk is available , and the a pdf file with the slides is posted here.

Cosmic Rays and their effect on earth

One interesting 'practical application' of cosmic-rays is in how they may affect life on Earth.

The obvious effect is that cosmic-rays are responsible for a good chunk of the background radiation that we experience on earth (the Earth itself is responsible for most of the rest, in the form of natural radon gas, etc.).

Of course, a dramatic short-term increase in the background radiation is dangerous. An overly nearby supernovae or other high-energy astrophysical events would be deadly (but very, very rare); it has been speculated that they may be responsible for occasional mass extinctions.

The long-term effect of lower doses of radiation, as from cosmic-rays is less clear. Cells contain repair mechanisms which can repair chromosome damage if it occurs slowly enough, and experimental studies of low levels of radiation have not found an increase in mutations. But, increased radiation level could cause increased mutation rates, and it has even been speculated that moderately nearby supernovae could have aided human evolution. Of course, in the shorter term, most mutations are not beneficial. It has been argued that the increase in ground-level radiation during reversals of the Earth's magnetic field could lead to increased mutation, and possibly, even to extinctions.

These supernovae leave geochemical 'footprints' on earth. These footprints can be seen in the form of thin layers of otherwise rare isotopes and an increase in carbon-14 abundance. The changing production rate greatly complicates the use of carbon-14 for dating, and elaborate calibration curves have been needed to relate the measured carbon-14 abundance in artifacts with the actual age.

Of course, this is mostly speculation. Interesting and important speculation, but still speculation.

Neutrino 2010 - conference report

Neutrino 2010 was an interesting conference. There were no earthshaking new results, but there was steady progress on many fronts.

The most interesting new results came from the MINOS and MiniBoone experiments. These are both detectors that observe neutrinos produced by an accelerator at Fermilab, near Chicago. Both experiments are studying neutrino oscillations, whereby a neutrino produced with one flavor (electron, muon or tau neutrino) oscillates as it travels from the accelerator to the detector.

MINOS has observed a possible difference between how neutrinos and antineutrinos oscillate. If correct, this would be very surprising, signalling a big difference between matter and antimatter. Although this result got significant publicity, apparently due to a Fermilab press release, the difference was not statistically large, and almost everyone at the conference was happy to treat it as a likely statistical fluctuation, pending more data. The other anomaly, from MiniBoone is harder to characterize, but is also likely a statistical fluctuation.

Two other popular topics were searches for neutrinoless double beta decay, and progress toward enormous (100,000-500,000 ton detector) next generation detectors.

In neutrinoless double beta decay, a nucleus changes it's atomic number by two (i.e. germanium decays to selenium, or xenon to barium), emitting two electrons and no neutrinos. This is only possible if a neutrino can act as it's own antiparticle, so this would be a major discovery. If this process occurs, it is very rare, with a half live of well over 10**20 (10 to the 20th power) years. So, these experiments must monitor large quantities (typically 100 pounds to 1 ton) of material for long periods, with a sensitivity to observe even a handful of decays. This is not easy. We heard 6 talks on neutrinoless double beta decay, discussing a wide variety of possible methods.

Over the past two years, there has been considerable progress toward a very large detector to make precision measurements of neutrino oscillations. The U.S. version would be located in DUSEL, the Deep Underground Science and Engineering Laboratory, which is proposed to be built in an old gold mine in South Dakota. The Japanese are also pursuing a similar project on an island between Japan and South Korea (the location is chosen to be the optimal distance from the Japan Hadron Facility accelerator), and the Europeans are considering several projects at diverse sites.

My talk, on radiodetection of neutrinos, went well, and seemed well received. It was a tough talk to prepare, since I had to introduce the concept, and also cover experiments looking for neutrino interactions in the moon, and two types of experiments looking for neutrino interactions in Antarctic ice (including, of course, ARIANNA). I also had a chance to talk to a number of people who are interested in ARIANNA.



Although Athens is a very interesting city, June is not the optimal time for a visit. They were having a heat wave during the conference, and temperatures were in the high 90's or low 100's (depending on which source you looked at), and it was also fairly humid. Worse, there was a 3-day metro (subway) strike during the conference. This was quite disruptive, since many of us were taking the metro between our hotels and the conference center. Of course, during the strike, the busses were jammed past capacity, and taxis were hard to get.

This strikes was not an isolated incident; more strikes are planned to protest government cutbacks due to the budget deficit and the economic conditions imposed by the European/IMF bailout. The threat of strikes has trimmed the tourist trade (it is down about 15% according to what I've read), and Athens seemed less crowded than usual. My hotel was not overly full, and a fair fraction of the residents were neutrino physicists. My flight to Greece was half empty, and there seemed to be a number of parked Olympic Air planes at the Athens airport.

Neutrino 2010

It is now June; school is getting out, and the summer conference season is starting. The big conference for neutrino physicists, Neutrino 2010 (it's held every 2 years) is next week, in Athens, Greece. About 530 neutrino physicists will gather for a week, to hear the latest results on everything neutrinos. Talks will cover a results from accelerators (Fermilab, CERN...) and non-accelerator experiments, along with the latest theory.

One hot topics is neutrino oscillations, whereby a neutrino from one flavor (like an electron neutrino) oscillates, over time turning into another flavor, like a muon neutrino. There are three different flavors, connected by three different mixing angles, which give a neutrinos propensity to turn into a different flavor. The three flavors have slightly different masses; the mass differences control how long the conversion takes. There is also a phase angle which, if non-zero, would allow charge-parity (CP) violation in neutrinos. This might help explain why the universe is all matter, with no visible antimatter. One way to study this is to shoot
a beam of neutrinos from an accelerator to a distant detector, and measure the oscillation probability. Another way to study oscillations is to use naturally occurring neutrinos. Neutrinos produced by nuclear reactions in the sun have plenty of time to oscillate before arriving at the earth; this is how neutrino oscillations were initially discovered. Or, one can use neutrinos produced in cosmic-ray air showers, which may oscillate as they pass through the earth on their way to a detector like IceCube.

A number of non-accelerator experiment are looking for a process called neutrinoless double beta decay, whereby an atomic nucleus decays, producing two electrons; the nuclear charge changes by two. For example, ^36Germanium decays into ^36Selenium, plus two neutrinos. This process can only happen if a neutrino is something called a "Majorana particle" which means that it is it's own antiparticle. In any case, the half-life for this process must be very long, well over 10^{22} years, so, one need a very large chunk of germanium to study this.

Neutrino astrophysics is also represented at the conference, with a couple of sessions including talks on high-energy astrophysical neutrinos. I will be giving an overview talk on radio-detection of neutrinos, covering ~ half a dozen experiments, including ARIANNA. It was a challenge to squeeze this all into a 15 + 5 minute (15 to speak, 5 for questions) talk.

I'm not looking forward to the long plane-flight to Athens; this will occupy a good chunk of the weekend.

I will try to post more frequently during the conference, both on conference life, and on new results.