Ground-based radio arrays offer a promising future for the measurement of ultra-high energy neutrinos, including the prospect of reducing the radio-detection energy threshold to a level necessary to overlap with the high-energy range probed by IceCube (~1016 eV). Here we describe a phased array of antennas and beamforming electronics, which serves as a highly sensitive and directional trigger system for nanosecond-scale plane wave impulses. A prototype in-ice phased array was successfully installed during the 2017/18 austral summer at the South Pole in collaboration with the Askaryan Radio Array (ARA). The trigger array is a compact string of 7 in-ice dipole antennas deployed at a depth of 200 m, whose signals are continuously digitized at the surface using 1.5 GSa/s ADCs with 7-bit resolution. We measure a 50% trigger efficiency on band-limited impulses with signal-to-noise ratios of 2.0 or smaller.
Thermal effects on the absorption of ultra-high energy neutrinos by the cosmic neutrino background
