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

Abstract

Ultrahigh energy neutrinos are interesting messenger particles since, if detected, they can transmit exclusive information about ultrahigh energy processes in the Universe. These particles, with energies above 10 16 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 the 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 three deep ARA stations are deployed in the ice, of which two have been taking data since the beginning of 2013. In this article, the ARA detector "as built" and calibrations are described. 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 1.5 × 10 −6 GeV=cm 2 =s=sr is calculated for a particle energy of 10 18 eV, which offers promise for the full ARA detector.

First results from two deep Askaryan Radio Array stations

“…In the following, a summary of the analysis will be presented. More details can be found in [9]. Simulated neutrino events, used to train analysis algorithms and to calculate the detector effective area and sensitivity, are generated with the AraSim code [11].…”

“…The signal chain noise figure has been measured at room temperature and is extrapolated to the colder environment. More details about the detector calibration can be found in [9]. The data analysis is performed in two main steps.…”

“…Figure 3: The ARA 2 station neutrino limit for 7.5 months of operation compared to other detector limits and flux expectations. The projection for the ARA37 sensitivity is calculated at trigger level without accounting for systematic errors [9,10,13,14,12,15,16,17,18].…”

“…To minimize overlap between stations and, thus, maximize the effective area of the full detector the stations are distributed in a hexagonal structure with a spacing of 2 km. More details about the ARA stations and their performance can be found in [7,9]. Currently, 3 ARA stations and a prototype are deployed at the South Pole.…”

Askaryan radiation from neutrino-induced showers in ice

“…4, where we compare the vector potential as obtained with Eq. (16) for different values of the fraction of neutrino energy transferred to the nucleus, y, with those obtained directly in full ZHAireS simulations of ν e -induced showers in ice. The difference between the fit and the ZHAireS simulations is at the ± 3% level in the time range spanning the dominant part of the peak.…”