Searches for exotic particles at HERA

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Searches for new particles and new phenomena were carried out through the ZEUS collaboration at the electron-proton collider HERA at DESY.During the fiscal year 1995, the collider was operated for physics at the total center of mass energy of 300 GeV from May to November. The ZEUS detector performed well to record a total luminosity of about 7 pb^<-1>. The data is now being reconstructed. In parallel analyzes of the data which had been obtained till last year have been continues giving the following results.^<**>The cross sections of deep inelastic scattering have been measured both for the neutral current reactions and the charged current reactions. In the region for Q^2 above 10^4 GeV^2, the effect of the W/Z boson mass can be observed. The u-quark and the d-quark contributions could be separated through the comparison of the e ^-p and the e ^+p data. The cross sections are consistent with the expectations of standard model thus giving upper limits on the possible contact interactions. Depending on the type of coupling, the obtained limits on the cut-off ranges between 1000 GeV and 1800 GeV.^<**>A systematic search for excited fermions have been made. No evidence was found and limits on the coupling constant was obtained for the mass range between 50 and 250 GeV.^<**>Hard jet production in the photoreaction was investigated. This study is important in order to study W/Z production by means of their hadronic decays.^<**>Hard isolated lepton (s) with a large transverse momentum was searched for. They give a clue for exotic particles. Some candidates were found which are consistent with the production and leptonic decay of W/Z bosons.^<**>Systematic investigations of the events with a large rapidity gap were continued both for the deep inelastic scattering and the hard photoproduction.