Study of e-p collisions by the ZUES international collaboration

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Elementary Particles and their interactions are studied with the ZEUS international collaboration at the e-p collider HERA built at DESY, Germany.The universal purpose ZEUS detector with a superconductive solenoid coil was constructed by the collaboration. Major detector components including high resolution calorimeters, a central tracking chamber and muon chamber system were completed within the fiscal year 1991. After being rolled in into the enteraction region, the detector was tested with cosmic rays for data taking.From May to June, 1992, HERA was operated for physics for the first time. Investigation of backgrounds from various origins was started in order to reject as much background as possible at trigger level so that data taking be made efficiently. This was done successfully by means of time information from a beam counter and the calorimeters. Data taking was made twice, in early summer and autumn, with 820 GeV protons and 26.6 GeV electrons. In total an integrated luminosi … More ty of about 30 nb^<-1> was accumulated.Initial analyses of the neutral-current deep inelastic scattering and photoproductions were performed. The high center of mass energy allowed to study these reactions in the kinematical regions which had previously been inaccessible. For instance the total cross section of the photon-proton reaction was measured at 210 GeV, which is one order of magnitude higher than that of the existing data. It showed a slight increase but not a rapid rise as speculated based on some cosmic ray phenomena.Studies of the deep inelastic scattering provided new information on the proton structure function at very small scaling variable, x,where QCD can't be calculated in the present technique. The momentum transfer Q^2 was increased substantially reaching 10^4 GeV/c^2. So far no particular structure like a peak, which is expected if an exotic particle called leptoquark is produced, has been observed in the high Q^2 region. Limits on the masses for different cases were estimated. Less