Background studies for acoustic neutrino detection at the South Pole

TL;DR

This study assesses the ambient noise and potential for acoustic neutrino detection in Antarctic ice, using data from the South Pole Acoustic Test Setup over two years, to evaluate detection thresholds and set flux limits.

Contribution

It provides the first in-situ noise measurements and event localization in Antarctic ice, improving understanding of acoustic neutrino detection feasibility.

Findings

Noise is stable and Gaussian distributed.

Absolute noise level estimated below 20 mPa.

Upper limit on neutrino flux at >10^11 GeV derived.

Abstract

The detection of acoustic signals from ultra-high energy neutrino interactions is a promising method to measure the tiny flux of cosmogenic neutrinos expected on Earth. The energy threshold for this process depends strongly on the absolute noise level in the target material. The South Pole Acoustic Test Setup (SPATS), deployed in the upper part of four boreholes of the IceCube Neutrino Observatory, has monitored the noise in Antarctic ice at the geographic South Pole for more than two years down to 500 m depth. The noise is very stable and Gaussian distributed. Lacking an in-situ calibration up to now, laboratory measurements have been used to estimate the absolute noise level in the 10 to 50 kHz frequency range to be smaller than 20 mPa. Using a threshold trigger, sensors of the South Pole Acoustic Test Setup registered acoustic pulse-like events in the IceCube detector volume and its vicinity. Acoustic signals from refreezing IceCube holes and from anthropogenic sources have been used to localize acoustic events. Monte Carlo simulations of sound propagating from the established sources to the SPATS sensors have allowed to check corresponding model expectations. An upper limit on the neutrino flux at energies $E_\nu > 10^{11}$ GeV is derived from acoustic data taken over eight months.