Front-end Electronics for MPPCs for the KOTO CsI Calorimeter Upgrade

Abstract

The aim of the J-PARC KOTO experiment is to search for new physics beyond the standard model (SM) with the rare kaon decay K L ! (cid:25) 0 (cid:23) (cid:22) (cid:23) . The branching ratio of this decay is predicted to be 3 : 0 (cid:2) 10 (cid:0) 11 in the SM. The KOTO detector consists of an electromagnetic calorimeter made of undoped Cesium Iodide (CsI) crystals, and hermetic veto counters. To reach the sensitivity predicted in the SM, we need to suppress the background caused by beam halo neutrons by an additional factor of ten. We installed 4080 Multi Pixel Photon Counters (MPPCs) upstream of the crystals to discriminate neutrons and photons. In the KOTO detector, the MPPCs will be exposed to a dose of 1 : 5 (cid:2) 10 9 n 1MeV = cm 2 . We measured that radiation damage would not affect the operaion of the MPPCs in the experiment. For the updated calorimeter, we developed front-end electronics including MPPC connection, summing ampli(cid:12)er circuit for the signal, and control system.