An improved Shashlyk calorimeter

Shashlyk electromagnetic calorimeter modules with an energy resolution of about 3%/E(GeV) for 50–1000MeV photons have been developed, and a prototype tested. Details of these improved modules, including mechanical construction, selection of wave shifting fibers and photo-detectors, and development of a new scintillator with improved optical and mechanical properties are described. How the modules will perform in a large calorimeter was determined from prototype measurements. The experimentally determined characteristics of the calorimeter prototype show energy resolution of σE/E=(1.96±0.1)%⊕(2.74±0.05)%/E, time resolution of σT=(72±4)/E⊕(14±2)/E(ps), where photon energy E   is given in GeV units and ⊕⊕ means a quadratic summation. A punch-through inefficiency of photon detection was measured to be ε≈5×10-5(Θbeam>5mrad).