Performance of two Askaryan Radio Array stations and first results in the search for ultra-high energy neutrinos

TL;DR

This paper reports on the deployment, calibration, and initial data analysis of the Askaryan Radio Array (ARA) at the South Pole, setting a neutrino flux limit at ultra-high energies with early data from two stations.

Contribution

It provides the first detailed description and calibration of the ARA detector and presents initial neutrino flux limits based on early data, demonstrating the detector's potential.

Findings

Neutrino flux limit of 3 x 10^{-6} GeV/(cm^2 s sr) at 10^{18} eV from 10 months of data

Successful deployment and calibration of the first two ARA stations

Effective data reduction methods to distinguish neutrino signals from background

Abstract

Ultra-high energy neutrinos are interesting messenger particles since, if detected, they can transmit exclusive information about ultra-high energy processes in the Universe. These particles, with energies above $10^{16}\mathrm{eV}$, interact very rarely. Therefore, detectors that instrument several gigatons of matter are needed to discover them. The ARA detector is currently being constructed at South Pole. It is designed to use the Askaryan effect, the emission of radio waves from neutrino-induced cascades in the South Pole ice, to detect neutrino interactions at very high energies. With antennas distributed among 37 widely-separated stations in the ice, such interactions can be observed in a volume of several hundred cubic kilometers. Currently 3 deep ARA stations are deployed in the ice of which two have been taking data since the beginning of the year 2013. In this publication, the ARA detector "as-built" and calibrations are described. Furthermore, the data reduction methods used to distinguish the rare radio signals from overwhelming backgrounds of thermal and anthropogenic origin are presented. Using data from only two stations over a short exposure time of 10 months, a neutrino flux limit of $3 \cdot 10^{-6} \mathrm{GeV} / (\mathrm{cm^2 \ s \ sr})$ is calculated for a particle energy of 10^{18}eV, which offers promise for the full ARA detector.