  A search for narrow-width resonances that decay into electron+jet or
neutrino+jet has been performed with the ZEUS detector at 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 as a function
of the mass of a hypothetical resonance that has arbitrary decay branching
ratios into electron+quark or neutrino+quark. 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 Yukawa coupling of 0.1, leptoquark
masses up to 290 GeV are excluded.
