Development and production of the MCP-PMT for the Belle II TOP counter

A square shape multi-anode micro-channel-plate photomultiplier tube (MCP-PMT) was developed for the Belle II TOP counter. It has a 23×23 mm2 multi-alkali photocathode with a peak quantum efficiency (QE) of 28% around a wavelength of 360 nm. It has a 2×106 gain and is capable of detecting a single photon with a transit time spread (TTS) of 40 ps or less. The QE, gain and TTS were measured for each MCP-PMT to check the quality in the mass production of 550 MCP-PMTs. The lifetime of the MCP-PMT was extended to 10 C/cm2 by adapting the atomic layer deposition technique for the MCP coating. Other properties of the MCP-PMT are also discussed: the angle and polarization dependence of the QE, and the effects of charge sharing and cross-talk. A prototype TOP counter was tested with a 2 GeV/c positron beam. The distribution of the time of propagation was consistent with the calculated expectation which included those properties of the MCP-PMT.