Search for new interactions in e-p Collision

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We studied possible existence of new interactions in electron-proton collisions at HERA at DESY in Germany by using a multi-purpose detector built in an international collaboration ZEUS.In the first two years, we completed the construction of ZEUS detector. The high-resolution uranium-scintillator calorimeter was calibrated with cosmic muons and installed into the experimental hall. The first level global trigger system was built with a pipeline technology. RISC workstations were installed at INS for the preparation of physics analyses. Software for physics simulation, data reconstruction and event display had been installed, In order to determine the trigger algorithm, physics events as well as background beam-gas interaction events were extensively generated with Monte Carlo technique by using the workstations. An international collaboration was organized for the simulation in order to obtain huge data sample, mainly with institutes in Canada, Germany and the Netherlands.In the final year, the electon-proton collision experiment started. It turned out that the trigger studies performed in the preceeding years were very useful. The trigger hardware proved to be extremely flexible and reliable. The energy resolution of the calorimeter was found to be as good as designed. Although the collected amount of data was rather limited (50 nb^<-1>), we measured the proton structure function in new kinematical regions. It was shown that the quark density in the proton increased as the momentum fraction of the proton carried by the quark decreases. A search of leptoquark was performed with the high-momentum transfer neutral-current deep-inelastic events, The lower bound on the leptoquark mass could be set to 170 GeV, in case the coupling strength is the same to the electro-weak interaction.