Test and Developments of Crystals for a High-Resolution Electromagnetic Calorimeter for PANDA

The energy resolution of PWO crystals and their dependence on the incoming energy has been investigated. The crystals used were first prototype crystals of a new generation, characterized by a higher light yield. Two crystal types with different shape and light yield, manufactured by suppliers in China and Russia, were used. An experiments were performed on two cooled arrays of 3x3 crystals. Photon beams of eight different energies, ranging from 64 MeV to 715 MeV, were directed into the center crystals. Photo Multiplier Tubes were used to read out the response of the scintillators. The energy resolution was calculated using three different methods - FWHM, a two gaussian fit and a right side fit. The two Gaussian method delivered the lowest sigma value and also the lowest energy resolution. The obtained energy resolution for the Russian crystals was 1.61%/sqrt(E)+0.73% and similarly 1.58%/sqrt(E)+4.25% for the Chinese crystals