Timing calibration of the NEutrino Mediterranean Observatory

Abstract

This paper describes the timing calibration system for the NEutrino Mediterranean Observatory (NEMO) underwater neutrino telescope. The NEMO Project aims at the construction of a km3 detector, equipped with a large number of photomultipliers, in the Mediterranean Sea. We foresee a redundant system to perform the time calibration of our apparatus: (1) A two-step procedure for measuring the offsets in the time measurements of the NEMO optical sensors, so as to measure separately the time delay for the synchronization signals to reach the offshore electronics and the response time of the photomultipliers to calibration signals delivered from a pulser through an optical fibre distribution system; (2) An all-optical procedure for measuring the differences in the time offsets of the different optical modules by means of common light sources. Such a system can be extended to work for a very large apparatus, even for complex arrangements of widely spaced sensors. The NEMO prototyping activities ongoing at a test site off the coast of Sicily will allow the system described in this work to be operated and tested in situ this year.