BEAM TEST OF THE CSI(TL) CALORIMETER FOR THE BELLE DETECTOR AT THE KEK-B FACTORY

We studied the performance of a prototype electromagnetic calorimeter for the BELLE detector at the KEK proton synchrotron for an energy ran ge of 0.25-3.5 GeV. The prototype consisted of an array of 6 x 5 CsI(T l) crystals with 30 cm length (16.2 radiation lengths) and about 6 cm x 6 cm cross section. The scintillation light of each CsI(Tl) crystal was read out by two large-area PIN photodiodes and charge-sensitive pr eamplifiers attached at the rear face of the crystal. We measured the energy and position resolution for electrons and the e/pi separation f or two sets of matrix configurations: one corresponded to the center a nd the other to the edge of the barrel calorimeter. The overall perfor mance measured by the test proves that the prototype calorimeter is sa tisfactory for the use in the BELLE detector.