At present, experiments are being prepared to search for muon-electron conversion, COMET at J-Park (Japan) and Mu2e at Fermilab (USA), where a segmented electromagnetic calorimeter (ECAL) is one of the main detectors. The main task of the ECAL in these experiments is to measure released energy when registering a 105 MeV electron with a high-energy resolution (better than 5%). The principal feature of these experiments are large angles of incidence of the registered electrons on the end surface of cells of the calorimeter located in a magnetic field.



In this case, a 105 MeV electron will sequentially pass through a number of active and passive calorimeter elements, and energy resolution will depend on an incidence angle, fluctuations in the number of charged particles, and non-uniformity of crystal light yield. 

The report presents the results of measurements of prototype calorimeter parameters of the COMET experiment using cosmic muons. The values of light yield deviation along the crystal length and at the angles of 19 and 9 degrees are given. A preliminary estimate of energy resolution of the prototype calorimeter of the COMET experiment is made taking into account the non-uniformity of the detector response.