Updated Results from the RICE Experiment and Future Prospects for Ultra-High Energy Neutrino Detection at the South Pole

TL;DR

The paper reports updated limits on ultra-high energy neutrino flux from the RICE experiment over twelve years, studies ice properties affecting detection, and discusses future improvements with the ARA project at the South Pole.

Contribution

It provides the most recent limits on UHE neutrino flux, insights into ice properties affecting radio detection, and outlines future prospects with the ARA array.

Findings

No neutrino candidates found in 12 years of data.

Improved flux limits by a factor of two over previous results.

Ice layer reflections correlate with ice flow and affect radio transparency.

Abstract

The RICE experiment seeks observation of ultra-high energy (UHE; >100 PeV) neutrinos interacting in Antarctic ice, by measurement of the radiowavelength Cherenkov radiation resulting from the collision of a neutrino with an ice molecule. RICE was initiated in 1999 as a first-generation prototype for an eventual, large-scale in-ice UHE neutrino detector. Herein, we present updated limits on the diffuse UHE neutrino flux, based on twelve years of data taken between 1999 and 2010. We find no convincing neutrino candidates, resulting in 95% confidence-level model-dependent limits on the flux which improve on our previous (2006) results by a factor of two. We also report on ice properties' studies, including observation of radiowave reflections from layers internal to the ice sheet. We observe correlations of these reflections with the local ice flow direction, and also qualitatively verify the expected reduction in radio frequency ice transparency with increasing depth/temperature. A new experimental initiative (the Askaryan Radio Array, ARA) commenced at South Pole in 2010-11 will improve the RICE sensitivity (per unit time) by approximately two orders of magnitude.