Updated results from the RICE experiment and future prospects for ultra-high energy neutrino detection at the south pole

Abstract

The RICE experiment seeks observation of ultra-high energy ("UHE"; E ν > 10 17 eV) neutrinos interacting in Antarctic ice, by measurement of the radio frequency (RF) 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% confidencelevel model-dependent limits on the flux E 2 ν dφ/dE ν < 0.5 × 10 −6 GeV/(cm 2 s − sr) in the energy range 10 17 < E ν < 10 20 eV, or approximately a two-fold improvement over our previously published results. Recently, the focus of RICE science has shifted to studies of radio frequency ice properties as the RICE experimental hardware has been absorbed into a new experimental initiative (the Askaryan Radio Array, or 'ARA') at South Pole. ARA seeks to improve on the RICE sensitivity by approximately two orders of magnitude by 2017 and thereby establish the cosmogenic neutrino flux. As detailed herein, RICE studies of Antarctic ice demonstrate that both birefringence and internal layer RF scattering result in no significant loss of ARA neutrino sensitivity, and, for the first time, verify in situ the decrease in attenuation length with depth into the Antarctic ice sheet.

Telescope Array search for photons and neutrinos with the surface detector data

“…Neutrino flux at ultra-high energies is constrained by air shower [27,28,29,30], ice shower [31] and radio Cherenkov [32,33,34,35,36,37] experiments (see [38] for a review). At lower (PeV) energies, neutrinos of astrophysical origin are discovered by IceCube [39].…”

First results from two deep Askaryan Radio Array stations

“…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].…”

Non-collider searches for stable massive particles

“…This leads to coherent emission of Cerenkov radiation of wavelength similar to the transverse size of the shower: the Askaryan effect [391,392]. High-energy neutrino experiments based on this principle have been conducted, using data from the FORTE satellite [393], Earth-based radio telescopes pointed at the Moon [394,395], the ANITA balloon-borne radio antenna array, which hovered over the Antarctic landscape for one month [396], and the RICE radio antenna array buried in ice at the South Pole [397]. Ultrarelativistic charged SMPs moving through a medium undergo dramatic radiative losses, and the induced electromagnetic showers create coherent Cherenkov radiation in the radio frequency domain.…”

“…In the future, the ARA radio antenna is expected to improve the RICE sensitivity by approximately two orders of magnitude [397]. ANITA did a similar analysis where monopole selection was made by requiring a row of four successive trigger events within 500 ns.…”