Comparison between high-energy proton and charged pion induced damage in PbWO4 calorimeter crystals

A PbWO4 crystal produced for the electromagnetic calorimeter of the CMS experiment at the LHC was cut into three equal-length sections. The central one was irradiated with 290 MeV / c positive pions up to a fluence of ( 5.67 ± 0.46 ) × 10 13 cm - 2 , while the other two were exposed to a 24 GeV / c proton fluence of ( 1.17 ± 0.11 ) × 10 13 cm - 2 . The damage recovery in these crystals, stored in the dark at room temperature, has been followed over two years. The comparison of the radiation-induced changes in light transmission for these crystals shows that damage is proportional to the star densities produced by the irradiation.