Development of Shashlyk calorimeter for KOPIO

A large size electromagnetic calorimeter with an energy resolution of 3%/√E (GeV) for 100-500 MeV photons is one of the keystone elements of the KOPIO experiment. In this paper we describe the method of optimization of the Shashlyk module to achieve the required energy resolution. To optimize the calorimeter module design, a model for simulation of the energy resolution was developed. It includes the effects of shower evolution, light collection in scintillator plates, light attenuation in fibers, quantum efficiency of the photo-detector, threshold and noise in the readout system. This model was adjusted using the results of a 0.5-2 GeV/c positron test beam study of a calorimeter prototype with an energy resolution of 4%/√E (GeV). Possible improvements of the Shashlyk energy resolution to 3%/√E (GeV), the level required by KOPIO experiment, are discussed