Radio detection of ultra high energy neutrinos

Recent evidence for observation of the Greisen–Zatsepin–Kuzmin (GZK) cutoff in the cosmic ray spectrum has a number of profound implications for our understanding of high energy astroparticle physics. This GZK process itself produces neutrinos that are strongly believed to be both spectrally and spatially correlated to high energy cosmic ray particles above 100 EeV. In the 1960ʹs Askaryan predicted that spatially compact nature of electromagnetic showers produced from the interaction of such high energy neutrinos would lead to coherent Cherenkov radiation. In June 2006 these Askaryan effect predictions were verified for emulated EeV showers in a 7 ton ice target at SLAC. A number of current and future experiments are now actively exploiting this radio detection method to search for the “guaranteed” GZK flux of high energy neutrinos. None have yet been observed, though the sensitivity of the detectors is just now approaching the predicted range. The ANtarctic Impulsive Transient Antenna (ANITA) experiment, a long-duration balloon operating at an altitude of 37 km, flew for over a month during December 2006–January 2007, and again December 2008–January 2009. In the longer term, a large-scale terrestrial radio array opens the possibility to probe deep inelastic neutrino-nucleon scattering at center of mass energies well above those of any proposed future collider. Prototype instrumentation stations have been evaluated. Essential to the realization of these experiments has been the development of affordable instrumentation with adequate radio frequency performance.