Characterization of 750 Large Area Photomultipliers for the KM3NeT-Italia Towers

The KM3NeT European experiment is building a large volume underwater neutrino telescope in the depths of the Mediterranean Sea. Thanks to a dedicated funding by the Italian Ministry of Education, University and Research, named KM3NeT-Italia in its first phase, an eight-tower detector is under construction. It is equipped with 672 optical sensors, called “optical modules,” (OM) which represent the detection elements of the telescope. They are composed by a 13-in high-pressure resistant glass-vessel that contains a single 10-in photomultiplier. As the key sensor, all the characteristics of the photomultiplier have a severe impact on the performance of the whole detector. The selected photomultiplier was the 10-in R7081 photomultiplier tubes (PMTs) produced by Hamamatsu. In the frame of the OM mass production, performed in the INFN site of Catania, 750 photomultipliers have been tested by means of a dedicated test bench. This paper deals with the procedures and the main results of such massive measurements.