Search for resonance decays to lepton+jet at DESY HERA and limits on leptoquarks

Abstract

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