MRI: Development of the ARIANNA High Energy Neutrino Telescope Instrument

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The primary purpose of the ARIANNA Ultra-High Energy (UHE) Neutrino project is to observe ~40 cosmogenic neutrinos per year originated by the GZK mechanism with sufficient precision to determine their energy spectrum and interaction properties. The energy spectrum of GZK neutrinos provides important insight on the production mechanism and source distribution of the cosmic rays. In addition, a statistically significant measurement of the angular distribution of the diffuse cosmogenic neutrino signal can be used to infer the interaction cross-section at energies beyond those probed by Large Hadron Collider. While the physics of the GZK mechanism is straightforward (extragalactic UHE protons collide with cosmic microwave background photons, producing pions that eventually decay to neutrinos), answering how the cosmic rays were accelerated to very high energies is especially difficult because cosmic rays are bent by magnetic fields in our Galaxy, and their range is limited by the GZK mechanism to ~100 megaparcecs. There is now a long legacy of successful high-energy neutrino programs that utilize the abundant and transparent ice of Antarctica. In particular, ARIANNA relies on the detection of radio pulses generated after neutrino interactions in dense media by the Askaryan effect, capitalizing on several remarkable properties of the Ross Ice Shelf near McMurdo Station, the hub of U.S. Antarctic Program operations: (1) the ice is impressively transparent to electromagnetic radiation at radio frequencies, (2) the water-ice boundary below the shelf behaves like a good mirror to reflect radio signals from neutrinos in any downward direction, and (3) background noise levels were quite modest in the frequency band of interest. Its close proximity to McMurdo Station provides a number of suitable options for logistical support, and ARIANNA's scalable architecture allows it to follow the science. This award allows the project to develop the data acquisition electronics required by the ARIANNA autonomous stations. Experience gained in operating the hexagonal array with precision, low power electronics would frame the performance requirements needed to expand the array in the future. The project will continue contributing significantly to the training of next generation of scientists by integrating graduate and undergraduate education with technology and instrumentation development, field observations, and scientific analysis.