New developments of scintillating crystal-based hybrid single photon detectors (X-HPDs) for charged particle and neutrino detection applications

Scintillating crystal-based hybrid photon detectors have been demonstrated as viable single photon detectors since 1996 in the Lake Baikal neutrino telescope. Prior to this, the Philips XP2600 was developed under the DUMAND program, while more recently, developments at CERN have demonstrated the advantages of a true concentric geometry with a scintillator at the geometric centre of a spherical photocathode, giving almost 100% electrostatic collection efficiency over 3π solid angle coverage. We began the development of a new series of quasi-spherical crystal hybrid photon detectors (the Photonis XP2608 series) for use in the future KM3NeT cubic kilometer-scale deep sea neutrino telescope. The thrust of this R&D was to investigate the industrialization of the crystal hybrid photon detector to the point where it would represent a significant cost reduction per cubic kilometer of instrumented volume compared to conventional large photomultipliers, thereby allowing extremely large telescope target volumes. Such gains would arise through an all-glass envelope, `internal' processing of the photocathode, and from the use of an inexpensive scintillating crystal or deposited phosphor viewed by a small photomultiplier. Details of these developments are presented.