Measurement of acoustic properties of South Pole ice for neutrino astronomy

Abstract

South Pole ice is predicted to be the best medium for acoustic neutrino detection. Moreover, ice is the only medium in which all three dense-medium detection methods (optical, radio, and acoustic) can be used to monitor the same interaction volume. Events detected in coincidence between two methods allow significant background rejection confidence, which is necessary to study rare GZK neutrinos. In 2007 and 2008 the South Pole Acoustic Test Setup (SPATS) was installed as a research and development project associated with the IceCube experiment. The purpose of SPATS is to measure the acoustic ice properties at the South Pole in order to determine the feasibility of a future large hybrid array. The deployment and performance of SPATS are described, as are first results and work in progress on the sound speed, background noise, and attenuation.

Measurement of sound speed vs. depth in South Pole ice for neutrino astronomy

“…Such mode conversion would be suppressed if the incident angle were normal, but if the pinger was not in the center of the hole the incident angle was oblique and shear wave production was favored. Pinger pressure wave and shear wave identification and characterization are presented in detail in [7] In the 2008-2009 season the pinger was operated with a mechanical centralizer to keep it close to the center of the hole, and the shear wave production was suppressed in that data compared to the 2007-2008 data analyzed here. The transmission (for both pressure and shear waves) and reflection (for pressure waves only) coefficients in terms of the incident angle are given by the Zoeppritz equations [22].…”

“…Such transients have been detected in coincidence between multiple sensors hundreds of meters apart. Using the sound speed profile presented here, the location and emission time of these acoustic sources can be reconstructed precisely [7].…”

“…Antarctic ice is even more transparent in radio wavelengths [4], [5], and the Radio Ice Cherenkov Experiment (RICE) [6] was operated to search for radio signals from astrophysical neutrinos. In situ measurements of the acoustic attenuation length in South Pole ice are underway [7].…”

“…In addition to pure interest in elastic materials physics, the measurement has applications to both geophysics [15], [16] and neutrino astronomy [7]. At the South Pole, one measurement was made previously for pressure waves at seismic frequencies, for depths between 0 m and 186 m (i.e., in the layer of uncompactified surface snow, or "firn"), using surface explosions [17].…”

Simulation of a hybrid optical-radio-acoustic neutrino detector at the South Pole

“…The radio and acoustic detection methods are currently in an intensive R&D phase, with several experiments (RICE [3], AURA [4] and SPATS [5,6]) underway to measure in situ the parameters necessary to establish the optimal geometry for a large detector.…”