Study of the light collection efficiency in the CMS ECAL PbWO4 crystals

The light collection efficiency in the crystals of the CMS lead tungsten Electromagnetic Calorimeter (ECAL) has a crucial role for the performances of the detector. It is of great importance to understand how radiation damage induced in the hostile Large Hadron Collider (LHC) environment will affect the collection of both the scintillation light and laser pulses of the monitoring system. We present the preliminary results of a Monte-Carlo study of the light propagation inside the crystals, focusing on two main aspects. First we validate the simulation with the crystal data collected during the ECAL construction phase. We then discuss the results of the simulation in terms of collection efficiency losses and mean photon path length in the crystal at different induced absorption lengths, both for barrel and endcap crystals. The results will be compared with the experimental data on the irradiation effect on the PbWO4 crystals.