Čerenkov light contribution in lead tungstate crystals

Results of detailed measurements of the Cerenkov light yield from lead tungstate (PbWO4) crystals are presented. A single crystal as well as a small homogeneous calorimeter (ECAL), consisting of 19 PbWO4 crystals, were exposed to electrons, muons and pions at the H4 beam line at CERN. It turns out that a significant fraction of the detected light is not the result of scintillation processes, but rather of the Cerenkov mechanism. This can be assessed from the analysis of both the angular dependence of the signals and their time structure. Detailed studies of the ECAL signals, corroborated by the measurements taken with the Dual-Readout calorimeter (DREAM), backing up the ECAL during beam tests, show that it is possible to estimate the independent contributions of scintillation and Cerenkov light. This information makes it possible to account for one of the dominant sources of fluctuations in hadronic showers and thus to achieve a significant improvement in hadronic calorimetry performance.