Collaborative Research: MRI-R2 Instrument Development of the Askaryan Radio Array, A Large-scale Radio Cherenkov Neutrino Detector at the South Pole

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). One of the most outstanding questions in astronomy and astrophysics addresses the origin and evolution of the cosmic accelerators that produce the highest energy (UHE) cosmic rays. This question may be best addressed through the observation of UHE cosmogenic neutrinos that travel from their source undeflected by galactic and interstellar magnetic fields and unimpeded by interactions with the cosmic microwave background (CMB) radiation. However, uncertainties in the predicted cosmogenic neutrino fluxes make it difficult to design an array with sufficient sensitivity to collect a statistically meaningful sample of events. At very high energies (above 10^15 eV), neutrinos could be most efficiently detected in dense, radio frequency (RF) transparent media via the Askaryan effect. The abundant cold ice covering the Antarctic, with its exceptional RF clarity, has been hosting several pioneering efforts to develop this RF approach. From the expertise gained in these experiments and utilizing the infrastructure developed by the U.S. Antarctic Program, it is proposed to develop radio-listening equipment that can constitute the Askaryan Radio Array (ARA) and install it in the ice near the geographical South Pole. The primary goal of the ARA array will be establishing the absolute cosmogenic neutrino flux through the modest number of events. As the proposed radio antennae are deployed in ice holes extending below the firn layer to 200-m depth, they will have the ability to distinguish surface noise from sources originating deep in the ice cap (otherwise not possible in balloon-borne experiments). The ARA will have sufficient sensitivity to establish the presence or absence of the secondary UHE neutrinos produced by the interaction of cosmic rays with CMB. Such an observatory would also provide a unique probe of long-baseline high-energy neutrino interactions unattainable with any manmade neutrino beam. The adopted clustered geometry of the array (in which a single localized cluster may act as a standalone array) would allow trading the precise angular resolution for the increased event rates. The flux measurement and experience gained in operating the limited number of stations would frame the performance requirements needed to expand the array in the future to measure a larger number of neutrinos with greater angular precision in order to study their spectrum and origins. The project will continue contributing significantly to the training of the next generation of scientists by integrating graduate and undergraduate education with the technology and instrumentation development.