Performances of a new directional optical module

The goal of the future KM3NeT neutrino telescope in the Mediterranean Sea is the investigation of the high energy component of the cosmic neutrino spectrum: a promising tool to better understand the mechanisms that generate extreme energy cosmic rays. Neutrino energy and direction will be reconstructed using the Cherenkov light produced in water by neutrino induced muons. In the framework of the EU funded KM3NeT Design Study, a new design for a large (10'') 4-anode photomultiplier has been developed. A prototype manufactured by Hamamatsu has been integrated into a spherical glass pressure-resistant optical module. It will be used for the first time to detect the direction of the detected Cherenkov light at one of the candidate site for KM3NeT, near Capo Passero in Sicily. The photocathode surface in these optical modules has been effectively divided into four quadrants by a pair of crescent shaped mirrors embedded in the optical gel linking the photomultiplier to the glass sphere. A series of measurements was performed at the testing facility of the NEMO group in Genova. The light collection and the angular response of the prototype have been studied, to have a complete characterisation and allow a comparison with previous models. The results of tests of the optical module are presented here.