Design, Implementation and First Results of the ANITA-HiCal Experiment

Abstract

The ANITA (ANtarctic Impulsive Transient Antenna) experiment is a balloon-borne suite of radio frequency antennas deployed during the austral summers in 2006, 2011, 2014, and 2016 to travel on the circumpolar winds over the ice sheets of Antarctica. The goal of the ANITA experiment is to detect UHE (Ultra-High Energy) neutrinos $(10^9$ to $10^{13}$ GeV) and cosmic rays through the RF (Radio-Frequency) emission of in-ice and atmospheric particle showers initiated, respectively, by these two types of particles. Radio detection of ultra-high energy cosmic ray (UHECR) extensive air showers (EAS) above the Antarctic continent has been demonstrated by the four flights of the ANITA experiment. The majority of the detected events were received as reflections from the ice surface. In order to reconstruct the energy of these reflected events, it is necessary to quantify any decoherence in the ANITA frequency band (180-1200 MHz) due to roughness of the ice surface. The purpose of this work is to provide details on the HiCal (High-altitude Calibration) experiment implemented to measure surface reflectivities of the Antarctic ice as a part of the ANITA experiment. The first HiCal payload flew in conjunction with the ANITA-3 flight in 2014 and provided a set of direct and reflected event pairs from which an inclination angle dependent measurement of the surface reflection coefficients was determined. It was found that at the highest incidence angles (most skimming) this coefficient deviates significantly both from the Fresnel predicted coefficients and from the model derived coefficients currently used in the ANITA analysis reconstruction of UHECR events.