Construction and beam test of a small compact electromagnetic PbWO4 calorimeter

A compact homogenous electromagnetic calorimeter with an energy resolution of better than 5%/E/GeV, made out of lanthanum-doped lead tungstate crystals from Bogoroditsk, Russia, has been built for use in the ZEUS detector. The whole calorimeter, composed of 4×4 crystals, each of dimensions 23.8×23.8×200 mm3, light guides and photomultipliers, fits into a space of 12×12×27 cm3. Beam tests with electrons up to 100 GeV showed an energy resolution of better than 4.9%/E/GeV, a linearity of better than 1% and a position resolution of 1.1 mm. The influence of temperature variations and recovery of an irradiated crystal on the total energy signal could be corrected to better than 1%. EGS4 simulations reproduce the results very well.