Experimental Study of Elementary Particle Physics by the Electron-Proton Collider HERA

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The purpose of this research program is to study elementary particle physics by means of electron-proton collisions at HERA, the first e-p collider ever built. The center of mass energy of the collider is 314 GeV, which enables to open such new fields to investigate the proton structure functions at very large Q^2 and/or very small x regions or to clarify the detailed properties of electro-weak interactions at very short distances. These studies require among others a high quality sophisticated detector system which can detect different types of secondary particles in a hermetic way. This program concentrated for the last three years to build an universal detector ZEUS to fulfill the requirement. Activities included ;1) Construction of a high quality hadron calorimeter system, 2) R&D of an electron-hadron separator using a Si-diode array, 3) Development and construction of a global first level trigger (GFLT) system and 4) Establishment of simulation software and studies of trigger cond … More itions using simulated events.Some details and achievements are described for each item.1) CalorimeterBasic R&D works were finished before this program. In this program efforts are made to construct calorimeters. By now all forward and rear calorimeters have been completed, tested and installed into the experimental hall. Photomultipliers were tested with a computer controlled test system and a new scheme was developed to supply high voltage to them.2) Hadron-Electron SeparatorAll the basic studies have been completed for the detector, mechanics and electronics. Tests were made with a small detector sample inserted in the prototype calorimeter.3) GFLTIn order to cope with the high rate of collisions (10MHz), a pipe-lined design was employed so that a long enough computation time (5 musec) is available for trigger decisions. The system has been constructed and the tests of communication with the detector components are progressing. The test made so far with some components proved to be successful.4) SimulationsElaborated software are being prepared to simulate physics reactions and detector responses. They were installed into the computer system of INS, where a substantial cpu time is available. Both deep inelastic scattering events (neutral current and charged current) and background events were produced in collaboration with other institutions. They were used to study trigger conditions to eliminate the beam-gas background effectively.All activities were carried out in a close collaboration with the foreign collaborators. Since much work were made at home, discussions and combined efforts at the experimental cite were essential in order to unify the accomplishments made at different institutions. Less