Feasibility of acoustic neutrino detection with the South Pole Acoustic Test Setup

Current experiments in astroparticle physics span over more than 13 orders of magnitude in energy and 28 orders of magnitude in flux. They make use of the detection of all types of messengers in order to learn more about the sources of these cosmic rays, the properties of the interstellar medium, as well as the nature of the particles themselves. The feeble interaction of neutrinos with matter makes them uniquely valuable as astronomical messengers. Unlike photons or charged particles, neutrinos can emerge from deep inside their sources and travel across the universe without interference.However, this same trait makes cosmic neutrinos extremely difficult to detect. Immense instruments, using natural resources as detector medium, are required to find them in sufficient numbers. Antarctic polar ice has turned out to be an ideal medium for detecting neutrinos. It is exceptionally pure, transparent and free of radioactivity. The density of detectors in such large neutrino telescopes is dictated by the attenuation length of the observable signal that is generated by the neutrino interaction with the medium. The optically transparent ice at the geographic South Pole has optical attenuation lengths in the order of 100m. This has allowed the construction and operation of the kilometer-scale neutrino detector, IceCube. However, the optical attenuation length and therefore detector cost is prohibitive to a possible extension towards the even larger detector volumes that are needed to detect the astrophysical neutrinos of the highest energies. Both the attenuation length of radio and acoustic waves are predicted to be larger than 1km in ice and both signatures are generated in an UHE neutrino interaction. Hence, this interaction in ice could be detected by an hybrid detector array consisting of optical, radio and acoustic sensors. The aim of presented work is to investigate the feasibility of an acoustic neutrino detection array situated in th South Polar ice. To this end, the acoustic properties of the ice in the 1 to 100kHz region were measured with a dedicated acoustic test setup:the South Pole Acoustic Test Setup (SPATS). The SPATS measurement of the acoustic attenuation length of the Antarctic ice using inter-string data is presented. This attenuation length is a fundamental quantity in determining the design and sensitivity of a future acoustic neutrino detector at South Pole