Experimental calibration of the ARA neutrino telescope with an electron beam in ice

Askaryan Radio Array (ARA) is being built at the South Pole aiming for observing high energy cosmogenic neutrinos above 100 PeV. The ARA detector identifies the radio emissions from the excess charge in a particle shower induced by a neutrino interaction. Such a radio emission was first predicted by Askaryan in 1962 and experimentally confirmed by Saltzberg et al. using the SLAC accelerator in 2000. We performed an experiment, ARAcalTA, using 40 MeV electron beams of the Telescope Array Electron Light Source located in a radio quiet open-air environment in Utah to verify our understanding of the radio emission and the detector responses used in the ARA experiment. We irradiated an ice target with electron beams. Radio signals from the ice target were clearly observed. The coherences, the polarizations and the angular distributions of the radio signals were measured to characterize them. We also performed a detailed simulation of the radio signals and found that the observed radio signals are consistent with the simulation, meaning that our understanding of the radio emission and the detector responses are within the systematic uncertainties of the ARAcalTA experiment.