TEST-RESULTS OF AN ELECTROMAGNETIC CALORIMETER WITH 0.5 MM SCINTILLATING FIBERS READOUT

We report on an experimental study of the performance of an electromag netic calorimeter consisting of thin (0.5 mm diameter) scintillating p lastic fibers embedded in lead. Because of the small sampling fraction (3.5% for minimum ionizing particles), this detector is quite compact , with an effective radiation length of 7.2 mm and a Moliere radius of 20 mm. Because of the very frequent shower sampling provided by the f ibers, the energy resolution is nevertheless good: 9.2%/root E(GeV) fo r electromagnetic (e.m.) showers, with a small, angle dependent consta nt term. A non-uniformity in the response is observed at the 2% level across the calorimeter. In spite of the small sampling fraction the li ght yield is not a limiting factor in this calorimeter: we measured si milar to 500 photoelectrons per GeV shower energy. The position resolu tion for electrons and two e.m. showers separation have been studied. The fibers sticking out of the back of the detector do not appear to a ffect the measurements of hadronic showers.