Development of positron detector for μSR based on multi-pixel photon counter

In the pulsed muon facility (MUSE) being built as a part of J-PARC, muon beams with unprecedented intensity (∼106 μ+/pulse) will be delivered at its full operation. Because of the extreme instantaneous μ–e decay positron rates (∼104–105 e+/pulse), development of a highly segmented positron detection system is crucial for practical application of μSR. To this end, we have designed a new positron detector based on a multi-pixel photon counter (MPPC). The advantages of MPPC over conventional phototubes are its small size, low operation voltage, functionality under a high magnetic field, and low cost. The result of test experiment for the detector using a pulsed muon beam is reported.