Detection of monochromatic photons between 50 and 790 MeV with a PbWO4-scintillator array

The performance of PbWO4 as a fast an compact scintillator material for calorimetry at energies well below 1 GeV has been investigated using a collimated beam of monoenergetic photons with an energy between 50 and 790 MeV provided by the tagged photon facility of MAMI at Mainz. In continuation of previous experiments with electrons, a larger matrix of 5x5 PbWO4-crystals (20x20x150-200mm(3)) has been used to reconstruct the electromagnetic shower. The scintillators were selected according to their optical quality and response to low energy gamma-sources. The array was operated at a stabilized temperature of T = 8 degrees C and read-out individually by photomultiplier tubes. The achieved excellent energy resolution amounts to sigma/E = 1.54%/root E + 0.30% (E given in GeV) and has proven the applicability of PbWO4 as a high quality scintillator material even at medium energies. The experimental data have been reproduced by GEANT3 simulations.