A search for resonance decays to lepton + jet at HERA and limits on leptoquarks

A search for narrow-width resonances that decay into electron+jet or neutrino+jet has been performed with the ZEUS detector at the DESY ep collider HERA operating at center-of- mass energies of 300 and 318 GeV. An integrated e(+)p luminosity of 114.8 pb(-1) and e(-)p luminosity of 16.7 pb(-1) were used. No evidence for any resonance was found. Limits were derived on the Yukawa coupling lambda as a function of the mass of a hypothetical resonance that has arbitrary decay branching ratios into eq or nuq. These limits also apply to squarks predicted by R-parity-violating supersymmetry. Limits for the production of leptoquarks described by the Buchmuller-Ruckl- Wyler model were also derived for masses up to 400 GeV. For lambda=0.1, leptoquark masses up to 290 GeV are excluded.