14 January 2015 An IceCube primer, webcast and another day with IceTop

As promised, today's post will be to explain what the IceCube NeutrinoAn elementary particle with zero charge and zero mass. An electrically neutral particle that is often emitted in the process of radioactive decay of nuclei. Neutrinos are difficult to detect, and their existence was postulated twenty years before the first one was actually discovered in the laboratory. Millions of neutrinos produced by nuclear reactions in the sun pass through your body every second without disturbing any atoms. ObservatoryA location used for observing terrestrial and/or celestial events. actually does, and why this is important. I will also summarize the events of the day.

The IceCube NeutrinoAn elementary particle with zero charge and zero mass. An electrically neutral particle that is often emitted in the process of radioactive decay of nuclei. Neutrinos are difficult to detect, and their existence was postulated twenty years before the first one was actually discovered in the laboratory. Millions of neutrinos produced by nuclear reactions in the sun pass through your body every second without disturbing any atoms. ObservatoryA location used for observing terrestrial and/or celestial events. is the world's largest and strangest telescope. Hosted by the Wisconsin IceCube Particle AstrophysicsBranch of astronomy devoted to the study of the physical characteristics and composition of objects in the sky, including how much light the stars give off and the size, mass, and temperature of planets and stars. Center (WIPAC), IceCube is an international collaboration involving over two dozen institutions. It was built over a six-season period between 2005 and 2010 just next to the Amundsen-Scott South Pole Station. The main purpose of the observatory is to study and measure high-energy neutrinos originating from astrophysical sources, such as supernovae, gamma ray bursts, neutron stars and accretion disks around black holes. Neutrinos are lightweight, fast and highly penetrating subatomic particles that rarely interact with matter. Trillions of neutrinos travel, unnoticed, each second through a person's body. Among the sources for neutrino generation are thermonuclear processes, which also produce high-energy photons such as gamma rays and X-Rays.

This is important because extreme astrophysical events are not always observable using regular telescopes. Photons can be weakened or even stopped by intervening matter. But neutrinos, with their amazing penetrating power, make the ideal messenger particle to study these extreme events. So far in its operation, IceCube has recorded 37 meaningful neutrino events of astrophysical origin.

IceCube uses 5,160 sensors (otherwise known as DOMs) hanging from 86 cables, that can detect and measure blue Čerenkov light produced by neutrino interactions. Although neutrinos themselves cannot be directly measured, when they hit an atom—or more precisely, protons or neutrons in atomic nuclei—they give out secondary particles like muons, that in turn produce a trail of Čerenkov light that can be measured. The energy content and the direction of the originating neutrino can be ascertained by studying this light.

The 5,160 IceCube sensors are buried below the South Pole surface, inside a cubic kilometer of ice which is the cleanest and optically purest on Earth. This is possible because the Antarctic Plateau—where the South Pole sits at—is actually a huge glacier that rises three kilometers above the bedrock. IceCube sensors were inserted using hot water drills at depth ranging from 1.4 to 2.4 kilometers.

Early in the morning today we did the first of two scheduled IceCube webcasts with me and the IceCube team live from the South Pole. We were informed that a large number of school and colleges were joining, from Puerto Rico and every part of the United States, and also from Italy, Pakistan and India. What most people did not actually realize was that for us the webcast was done at 4:00 am! Since both the McMurdo and Amundsen-Scott stations are synchronized with New Zealand time, we at the South Pole are 17 hours ahead of Atlantic Standard Time which is in use in Puerto Rico. We all had a good time with the webcast, and a number of us were actually able to get a few additional hours of sleep after the event.

Later during the morning I went out with Sam to assist him in taking measurements on the surface tanks that make up the IceTop array. We drove the snowmobile and arrived at the same IceTop location we had been yesterday. It was cold, cloudy and windy, but we felt fine as our stay outside was brief. As explained yesterday, IceTop consists of 162 cylindrical tanks of ice, each equipped with two standard IceCube sensors capable of detecting and measuring cosmic rays. Since IceCube can also study cosmic rays—in addition to neutrinos—the deployment of IceTop will supplement cosmic ray data detected deep in the ice with data from the surface.

After lunch we went to the IceCube Laboratory (ICL) where we picked up some electronics and cables, and then set to the field again. The weather began to improve and clouds started to break. Winds subsided and we started feeling the warmth of the Sun. By 4:00 pm it was mostly clear and much warmer than it had been in the morning. We did some measurements and also plugged some cables in and out, and the warmer weather was a treat because our hands stayed warm throughout. We stayed outside for much longer than in the morning, but surprisingly were able to work very comfortably.