Photon Transmission In Shashlik Electromagnetic Calorimeter For Nica-Mpd

A simulation program based on GEANT4 is developed to study the performance of the shashlik electromagnetic calorimeter, which is a part of the multi purpose detector at nuclotron-based ion collider facility (NICA-MPD). The whole process is considered, including electromagnetic shower, scintillation process, wavelength shift (WLS) effect and photon transmission, which itself includes reflection, refraction, absorption and transport of optical photon. The program is used to analyse the factors affecting the number of photoelectrons (Npe) of the silicon photomultiplier (SiPM), e.g. the degree of polishing of optical surfaces, and the width of the gap between the reflective layer and the end surface of fibers. The simulation results show that the Npe is larger when the shashlik tower is wrapped with specular reflection material, instead of the diffuse reflective material used in the current design. Concerning the end of the fibers, we find that the encapsulation method, where the fiber is pulled to a specular layer, provides better performance than coating the end of fibers by diffuse reflective material.