Monte Carlo study of performance of BES III CsI crystal calorimeter

In the process of design and research of BES III crystal calorimeter, we made a detailed Monte Carlo study for the performance of BES III Csl crystal calorimeter on the basis of the detection cell of 7 x 7 CsI matrix. Results are presented on incoherent noise, on energy linearity, on uniformity of the crystal light output, on position dependence. Those results show that the energy resolution of the 5 x 5 matrix sum is about 2.1% for 1 GeV photon and the best energy resolution of the lower energy photon is obtained with the energy threshold of 2.5 sigma(noise). The energy deposit in the matrix decreases by about 1% and the energy resolution degrades by about 0.3% when 800MeV photons are injected in the gap region between two crystals. The average position resolution is about 6.3 mm at 800 MeV.