Searching for Ultra-High Energy Neutrinos with ANITA
ANITA (the ANtarctic Impulsive Transient Antenna) is a long-duration balloon borne radio interferometer designed to search for ultra-high energy (> 10^18 eV) cosmogenic neutrinos. Over a few weeks it flies at an altitude of 37km, scanning the Antarctic ice for Askaryan radio emission created by neutrino interactions. To date four science flights have been completed, with a fifth flight proposed for the near future. In this talk I give an overview of ANITA with a focus on the third and fourth flights and discuss the recently completed analyses of ANITA-3 data.
The most sensitive neutrino search from ANITA-3 found a single neutrino candidate event on an expected background of 0.7 (+0.8 -0.3) events. The analysis set the best limit on the diffuse flux of ultra-high energy neutrinos at energies above 10^19.5 eV. Although consistent with the initial background estimate, interpretation of the surviving event as a neutrino is still plausible after additional post-unblinding scrutiny.
The ANITA-3 analyses also found nearly 30 extensive air shower events in an alternative polarization to the neutrino search. All but one of these events are identified as ultra-high energy cosmic rays. We give a speculative interpretation of the remaining alternative polarization event.