Time calibration of the NEutrino Mediterranean Observatory (NEMO)

Large volume Cherenkov detectors are under construction or have been proposed for detection of astrophysical neutrinos under water or ice. In all such cases, the neutrinos are inferred from the detection of the Cherenkov light emitted by the charged leptons created in neutrino interactions inside or around the apparatus. The event reconstruction is thus based on charge and time measurements performed by a system of widely spaced optical sensors. The time calibration is a very delicate operation for such experiments, as it may directly affect the reconstruction efficiency and pointing capabilities of the apparatus. In this paper, we illustrate the systems under study for the km3-scale project NEMO (NEutrino Mediterranean Observatory), focusing on the implementations for the NEMO Phase-1 and Phase-2 prototyping campaigns.