Beam Tests of Lead tungstate crystal matrices and a silicon strip preshower detector for the CMS electromagnetic calorimeter

Further tests of lead tungstate crystal matrices made in high energy electron beams in 1996, using new crystals, new APDs and an improved test setup confirm that an energy resolution of better than 0.6% at 100 GeV can be obtained when the longitudinal uni formity of the struck crystal is adequate. Light loss measurements under low dose irradiation are reported. It is shown that there is no loss of energy resolution after irradiation and it is demonstrated that the calibration change due to light loss can b e tracked with a precision monitoring system. Successful tests with a preshower device, equipped with silicon strip detector readout, are also described.