An Improved Shashlyk Calorimeter

Shashlyk electromagnetic calorimeter modules with an energy resolution of about 3%/ √ E (GeV) for 50−1000 MeV photons has 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 ǫ ≈ 5× 10−5 (Θbeam > 5 mrad).