Calibration in acoustic detection of neutrinos

Abstract

Recent developments in acoustic detection of neutrinos have allowed being more optimistic about the possibility of using the technique in neutrino telescopes, but it still remains a technological challenge and the feasibility of this method has to be proven. Calibration has an important role in both, exploiting the technique at the very limit of the knowledge, and in performing the tests that assure its reliability. In this paper we review the different calibration techniques used (or possibly used) in the field. We can classify the calibration activities in two fields, in the lab and “in situ” in neutrino telescopes, covering a very broad range of topics. Acoustic sensors must be first calibrated in the lab in order to know the sensitivity and the time response of the sensors. Depending on constraints different techniques can or should apply. But lab calibration goes beyond this and involves, for example, the understanding of the thermo-acoustic pulse generation. In neutrino telescope sites, a calibration system with acoustic transmitters should be used to monitor the sensitivity and time response of sensors in site, as well as the response to neutrino-like signals. At the same time, it should provide not only a good tool for training the system for an optimized event reconstruction, but a test to the reconstruction as well. Different acoustic systems have been proposed, we will overview them putting especial attention to the use of acoustic transducers which seems the more versatile technique. Last, the positioning and synchronization of the hydrophones and the knowledge of the physical environment including medium properties are also considered as calibration tasks.