A Search for Leptoquark Bosons in DIS at HighQ2 at HERA H1 Collaboration

A search for new bosons possessing couplings to lepton-quark pairs is performed in the H1 experiment at HERA using 1994!1997 data corresponding to an integrated luminosity of 37 pb 1. The very highQ2 neutral (NC) and charged (CC) current data are first compared to Standard Model expectations from deep inelastic scattering. The deviations in the Q2 spectrum previously observed in the 1994!1996 data at Q2> 15000 GeV2 remain, though with less significance. No significant clustering in the mass spectra is observed with the 1997 data alone. The data are used to constrain the direct s-channel production of first generation leptoquarks. Compared with earlier HERA results, the exclusion limits are considerably improved for leptoquarks which could be produced via e+-valence quark fusion and extend beyond the coupling-mass domain covered so far at other colliders for a small branching ratio to e+q. For a branching ratio as small as 10%, masses up to 255 GeV are ruled out by the present analysis for a Yukawa coupling of electromagnetic size for the leptoquark to e+u pair. The analysis is then extended to cover also leptoquarks with mixed couplings allowing for decays into leptons of the second or third generation. None of the + jet or + jet event candidates are found to be compatible with the two body decay hypothesis of a leptoquark. Constraints are set on the Yukawa coupling involving the lepton for a mass range extending beyond the domain presently covered at other colliders. Abstract: 579 Parallel sessions: 10 Plenary sessions: 12 579 Parallel sessions: 10 Plenary sessions: 12