Study of high-transverse-monontum lepton productoin in ep collisions

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We have studied productions of leptons with high transverse-energy in electron-proton scatterings with the e-p collider HERA built at DESY in Germany. Any deviation in the cross sections compared with the predictions of the standard model could imply new phenomena such as the production of supersymmetric particles. Especially, when we started the project, an experiment reported a slight excess of high energy muon production so that further searches with the higher statistics were urgently awaited.In parallel to experimental searches with the data taken by ZEUS detector at HERA, basic theoretical studies were performed in order to understand sensitivity to new phenomena. It is planned to upgrade the HERA to get higher luminosity and to enable to use longitudinally polarized electron in the collision since 2002. The effect of the polarization in the production of supersymmetric particles are studied and found that the cross section is doubled.In order to estimate the rare background from the two-photon processes, a new Monte Carlo generator was developed.Searches for high momentum muons and taus were performed and found that it is consistent to the production from W boson decays. High momentum electron and neutrino productions were also consistent with the standard neutral- and charged- current interactions. From these results we set limit in the mass/coupling of supersymmetric particles, leptoquarks and excited fermions.