Outline of the Detector

Photo-Multiplier-Tubes (Outer detector)

Super-Kamiokande detector is optically separated into two concentric cylindrical regions by PMT support structures and pairs of opaque sheets. In the outer region, 1,885 outward-facing PMTs are instrumented. The PMTs of the outer detector(OD) are smaller than those of the inner detectors and the diameter is 8 inch (about 20cm). The OD PMT is attached to a 60cm x 60cm wavelength shifter plate in order to collect photons efficiently. The walls are covered with reflective white sheet.



The main purpose of the outer detector is to distinguish the neutrino events from the cosmic ray muon events. The cosmic ray muons are background sources of the neutrino observation. Because the neutrinos are electrically neutral, the Cherenkov light is emitted when the neutrinos scatter with the water. On the other hand, because the cosmic ray muon have an electric charge, the Cherenkov light is immediately emitted when the cosmic ray muon enters the detector. Therefore, in case of cosmic ray muons the OD PMTs almost have hits, while in case of neutrinos, the OD PMTs have few hits. This difference enables to roughly distinguish between neutrinos and cosmic ray muon events.

Details of PMTs




Outline of the Detector