Constraints on the Diffuse Flux of Ultra-High Energy Neutrinos from Four Years of Askaryan Radio Array Data in Two Stations

TL;DR

This study uses four years of data from the Askaryan Radio Array to set upper limits on the flux of ultra-high energy neutrinos in the Antarctic ice, improving previous constraints.

Contribution

It provides new constraints on the diffuse flux of ultra-high energy neutrinos using extended data from two stations, with improved sensitivity over prior results.

Findings

Placed a 90% CL upper limit on neutrino flux at 10^{18} eV

Analyzed four years of data from two stations (A2, A3)

Achieved four times the exposure of previous ARA results

Abstract

The Askaryan Radio Array (ARA) is an ultra-high energy (UHE, $>10^{17}$ eV) neutrino detector designed to observe neutrinos by searching for the radio waves emitted by the relativistic products of neutrino-nucleon interactions in Antarctic ice. In this paper, we present constraints on the diffuse flux of ultra-high energy neutrinos between $10^{16}-10^{21}$ eV resulting from a search for neutrinos in two complementary analyses, both analyzing four years of data (2013-2016) from the two deep stations (A2, A3) operating at that time. We place a 90 % CL upper limit on the diffuse all flavor neutrino flux at $10^{18}$ eV of $EF(E)=5.6\times10^{-16}$ $\textrm{cm}^{-2}$$\textrm{s}^{-1}$$\textrm{sr}^{-1}$. This analysis includes four times the exposure of the previous ARA result, and represents approximately 1/5 the exposure expected from operating ARA until the end of 2022.