First Results on Radiation Damage in PbWO_4Crystals Exposed to a 20, GeV/c Proton Beam

We have exposed seven full length production quality crystals of the electromagnetic calorimeter (ECAL) of the CMS detector to a 20 GeV/c proton beam at the CERN PS accelerator. The exposure was done at fluxes of 1012 p/cm2/h and 1013 p/cm2/h and integral fluences of 1012 p/cm2 and 1013 p/cm2 were reached at both rates. The light transmission of the crystals was measured after irradiation and suitable cooling time for induced radioactivity to decrease to a safe level. First results of these measurements are shown. The possible damage mechanisms are discussed and simulations based on one possible model are presented. The implications for long-term operation of CMS are discussed and it is shown that in the whole barrel and at least most of the ECAL endcap hadron damage alone -even if cumulative- should not cause the crystals to fail the CMS specification of $\mu_{IND} < 1.5m^{-1}$ during the first 10 years of LHC operation.