Multi-photomultiplier detectors in the Water Cherenkov Test Experiment

Abstract The Water Cherenkov Test Experiment (WCTE) at CERN was a prototype facility designed to evaluate technologies for water Cherenkov detectors, which will be used in the Hyper-Kamiokande experiment. WCTE was instrumented with 97 multi-photomultiplier (multi-PMT) modules, each containing 19 three-inch photomultiplier tubes (PMTs) and associated front-end electronics. In this work, we present the design and production of multi-PMT modules, the methods used for gain and timing calibration, and studies of PMT internal properties, including afterpulses and residual gas identification. Calibration procedures achieve sub-nanosecond timing resolution and uniform gain across modules. The data collected allow evaluation of particle identification capabilities and detector response to various charged particles, providing essential input for the design and operation of future large-scale water Cherenkov detectors.