Pulse shape discrimination of photons and neutrons in the energy range of 0.1 – 2 GeV with the KOTO un-doped CsI calorimeter

Abstract A pulse shape difference between photons and neutrons was observed in the output signals of scintillation light from the un-doped CsI calorimeter of the KOTO experiment for the K L → π 0 ν ν decay. We developed a discrimination method to reject neutrons and to accept photons in the deposited energy range from 0.1 to 2 GeV. The method rejects 67% of neutron-induced single hadronic clusters and 86% of neutron-induced two-cluster events while keeping more than 90% of photon-induced single electromagnetic clusters and two-photon events.