Observation of the Askaryan effect in ice with the Anita experiment

Abstract

First hypothesized by Gurgen Askaryan in the 1960's and later confirmed in 2001 at SLAC (Stanford Linear Accelerator Center), radio Cherenkov detection techniques are possible in the ultra-high energy regime (1018 -> 1022 eV) while observing electromagnetic cascades in dielectric media. This method of detection has now moved into the field of neutrino astrophysics. Recently, the interest in using ice as a dielectric medium to observe coherent microwave Cherenkov pulses from ultra-high energy neutrino induced particle showers has grown considerably with advances from experiments such as RICE, FORTE, and ANITA-lite. ANITA (ANtarctic Impulsive Transient Antenna), is a radio telescope designed to exploit this effect while looking for UHE neutrino interactions in Antarctic ice. In June 2006, ANITA observed these highly coherent radio impulses in SLAC's ESA (End Station A) with 28.5 GeV electrons interacting with a 7.5 tonne ice target to produce the EM shower. These first measurements of the Askaryan effect in ice were consistent with shower and electrodynamics simulations for ice and provided a clear indication that the radiation is coherent over the 200-1200 MHz frequency window. In addition to the ANITA payload in SLAC's ESA, four log-period dipole array antennas, two monocone antennas, and one high frequency gain horn (nominally 2.6-3.95 GHz) recorded impulsive events emanating from the ice target. I report on further analysis of coherent radio Cherenkov impulses using the standard gain horn and demonstrate that the results are fully consistent with theoretical expectations.