The time calibration system of KM3NeT: The laser beacon and the nanobeacon

Abstract

The KM3NeT collaboration has started the construction of a deep sea neutrino telescope in the Mediterranean with an instrumented volume of several cubic kilometers. The objective of the KM3NeT telescope is to observe cosmic neutrinos. For this, the detector will consist of a tri-dimensional array of optical modules, each one composed of a pressure resistant glass sphere housing 31 small area photomultipliers. An important element of the KM3NeT detector is the system for the relative time calibration between optical modules with a precision of about 1 ns. The system comprises two independent devices: a nanobeacon inside each optical module for calibration of optical modules in the same vertical detection unit and a laser beacon for the calibration of optical modules of vertical units. After a general introduction of the KM3NeT project, a detailed description of the KM3NeT time calibration devices is presented.