Development of Time-Zero Detector for PHENIX Expriment at RHIC

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1.2nd prototype detector consisting of 1"PMT with fine mesh-dynodes and a Quartz block mounted on the PMT window, was built and tested with a pion beam at KEK-PS.The shape of the radiator block was optimized to be a hexagonal shape with 3 cm long.2.3rd prototype detector which was composed, in one united body, of the optimum shaped radiator and an improved PMT on its cathode-dynode structure was newly designed and tested with the pion beam. It was found that pulse heights in a magnetic field drop by 30%, but timing resolution remains at the same level 50 ps under magnetic fields up to 3 kgauss.3. A Monte Carlo simulation code including the Beam/Beam Counter in the PHENIX detector was studied, and indicated that particle cross talks between neighbor detector elements may cause some problems under high particle multicity environments of the PHENIX experiments.4. The 3rd prototype detector was tested with a heavy ion beam at BNL-AGS,and it proved that even under such a high particle multiplicity, the time resolution of 50 ps level can be achieved.5. The simulation indicates that the Beam/Beam Counter with the 3rd prototype will provide the information of a collision time at the accuracy of 40 ps.6. A prototype detector has been operated for 85 days under a very hard condition of 15 muA anode current, which simulates a condition of very high counting rates for 1 RHIC year, but found no troubles at all.7. It was found a prototype detector after irradiation of 1 MR of gamma-rays works fine without any troubles.8. Finally, we have decided to adopt the design of 3rd prototype detector as the final one for the PHENIX,since every requirement for the PHENIX experiment has been cleared with it. In 1995, we start the mass production of it.