Energy resolution and its simulation for the ESC of BES

With data collected by the Beijing Spectrometer (BES) in the J/ψ, ψ' and Ds energy region, a lot of e+e- final state events are selected in the solid angle region covered by the endcap shower counters (ESC). Some characteristics of the ESC are analysed, such as the spectrum of pulse height for a single counter cell, the hit numbers in the ESC and in every reading layer of the ESC, the shower energies deposited in the ESC and in every layer of the ESC. The energy resolution of the ESC is obtained to be about 22%/√E(GeV). Based on the original frame of SOBER, a Monte Carlo simulation program for the ESC is developed with a dual Gaussian pulse height spectrum of the single counter cell. The electromagnetic cascades are calculated by the EGS4 package and a three-dimension magnetic field in the BES is included. The simulation results agree with experimental data well