High Energy Particle Astrophysics
With the discovery of the neutrino over 50 years ago, the idea emerged to build a detector large enough to study neutrinos from astrophysical sources. High energy neutrinos acting as cosmic messengers from the Universe represent a new tool to address some of the most exciting questions in extreme astrophysics, cosmic ray physics and particle physics.
The IceCube Neutrino Observatory, constructed at the South Pole, is the world’s largest neutrino detector. It provides a new window to the Universe for answering questions about phenomena as diverse as supernovae, dark matter, gamma ray bursts, and active galaxies. It will also produce new and exciting challenges—the history of astronomy shows that forays into new wavelength regions have invariably resulted in the discovery of new phenomena.
Neutrinos are notoriously hard to detect and large detector volumes are necessary to see a sufficient number during the lifetime of the detector. The IceCube in-ice detector consists of 5,160 digital optical modules deployed on 86 vertical strings buried 1450 to 2450 meters under the surface of the ice. The optical modules are outfitted with photomultiplier tubes that register the Cherenkov light produced by neutrino-induced muons going through the detector volume. The potential signal of astrophysical neutrinos is hidden in a large background produced by muons from cosmic ray interactions in the atmosphere. In IceCube, the Earth is used as a filter to search for upward going neutrino events.
IceCube continuously scans the skies for supernova explosions in our galaxy and, possibly, for the birth of the supermassive black holes that power quasars. Although IceCube was under construction for years and was recently completed in December, 2010, it has been providing data since the completion of the first nine string array in 2006. The completed detector will be operated for at least 20 years.
UW-Madison is the lead institution for the IceCube project funded by the Division of Physics and the Office of Polar Programs of the National Science Foundation. IceCube is a collaboration that includes participants from 39 institutions in both the United States and other countries around the world.
IceCube graduate students contribute to the design, construction and calibration of the hardware and software of IceCube, and have often traveled to the Amundsen-Scott South Pole Station to assist with deployment and maintenance. In Madison, aside from a strong involvement in all the science aspects of the experiment, from point-source studies and gamma ray bursts, to diffuse fluxes of neutrinos and supernova collapses, and astrophysical source modeling, we lead the data acquisition efforts and contribute to the preparation of all the tools for data analysis such as reconstruction of particle tracks and simulation. Along with faculty at UW-Madison, graduate students are also doing R&D for enhancements to IceCube, taking advantage of the long and successful history of an experiment at the South Pole. This includes the possibility of detecting the highest energy neutrinos by radio techniques.