Cosmic-ray Physics with IceCube

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The main goal of this project is to search for a signature in the energy-dependent composition of the primary cosmic rays of a transition from galactic cosmic rays to a higher energy population of particles from extra-galactic sources. While the primary mission of the IceCube Neutrino Observatory is to search for high-energy neutrinos of astrophysical origin by measuring events in the deep detector induced by neutrinos from below, the dominant signal in IceCube is due to downward events caused by cosmic-ray interactions in the atmosphere. By looking for events from below, IceCube uses the Earth as a shield against this downward background. With its surface component IceTop, IceCube makes a 3-D air shower array with important potential for studying the downward cosmic rays. The novel feature of the IceCube/IceTop air-shower array is its large acceptance for events observed in coincidence. IceTop will use the ratio of the signal in the deep detectors to the signal on the surface to measure the relative concentration of different groups of nuclei in the primary cosmic radiation in an energy range not accessible to direct measurements with satellites because of the low intensity. The angular dependence of showers measured by IceTop alone and other features of the data are also sensitive to primary composition. This gives a complementary sensitivity to composition that in principle will remove some of the model-dependence inherent in the simulations used to interpret the data. Continued reliance on postdocs and students provides a broader impact to this proposed research and firmly grounds this effort in its educational mission.