Testing a prototype BGO calorimeter with 100-800Â MeV positron beams

An electromagnetic calorimeter, BGOegg, composed of 1320 BGO crystals, has been constructed at the Research Center for Electron Photon Science, Tohoku University to study the structure of hadrons in detail using photo-induced reactions. The design of the new electromagnetic calorimeter and the basic characteristics of the manufactured BGO crystals are described. A performance test has been conducted for the prototype, which consists of 25 crystals arranged in a 5×5 matrix, using positron beams at energies ranging from 100 to 800 MeV. The obtained energy resolution is (σE/E)2=(0.63%)2+(1.15%±0.04%)2/(E/GeV)+(0.42%±0.03%)2/(E/GeV)2 at room temperature. The energy resolution corresponds to 1.38%±0.05% for 1-GeV positrons. The position resolution is found to be σr/mm=(3.07±0.03)(E/GeV)−0.202±0.008 which corresponds to an angular resolution of approximately 1° for 1-GeV positrons.