Test results from a prototype lead tungstate crystal calorimeter with vacuum phototriode readout for the CMS experiment

Abstract Tests of a prototype for the electromagnetic calorimeter (ECAL) of the compact muon solenoid experiment (CMS) at the large hadron collider are described. The basic unit for the endcap ECAL in CMS is a “supercrystal” of 25 lead tungstate crystals. Results are presented from tests of the first full-sized supercrystal in electron beams and in a 3 T magnetic field. The supercrystal was exposed to electron beams with energies from 25 to 180 GeV. An energy resolution ( σ E / E ) of (0.48±0.01)% was measured at 180 GeV.