Prototype of SiC beam monitor for the COMET experiment at J-PARC

Abstract We have developed a prototype of the muon beam monitor ( μ BM) for the COMET experiment at J-PARC. The COMET aims to search for the neutrino-less muon-to-electron conversion event in the field of the nucleus, as a charged lepton flavor violation process. The SiC-based μ BM will be installed in a vacuum chamber and located in front of the muon-stopping target and the main central drift chamber. The detector consists of SiC PN-diodes and dedicated readout electronics. By tailing the 256 sensors in a matrix, the beam profile and bunch stability can be extracted, and then, are utilized for the background estimation of the rare process. To validate the μ BM concept, we implemented the SiC sensors on the prototype Kapton-flex sensor board and conducted a beam test at J-PARC. The pulse height of μ -events in the SiC sensor was linearly correlated with an averaged coincidence of the decayed electrons by scintillators. We thus conclude that the number of incident muons can be estimated from the pulse height information from the μ BM. The radiation tolerance of the sensor was also proven to be sufficient for the COMET Phase-1 by irradiating fast neutrons with 1.7×10 12 / cm 2 fluence at research nuclear reactor. The electronics designed in 65 nm CMOS is currently under testing. In the lab.-testing, we confirmed the basic functionality as a required waveform digitizer and sufficient signal-integrity to drive the 10 m cable length to the backend electronics.