Search for leptoquarks with the ZEUS detector

Abstract A search for any resonant state coupled to an electron and a proton constituent has been performed using collisions of electron and proton beams at HERA. In a sample with integrated luminosity of 26 nb −1 , no evidence has been found for production of leptoquarks with decays to e − + jet or ν + je to electron and quark have been determined for masses above 25 GeV. For example, scalar isosinglet leptoquarks ( S 0 ) with electroweak coupling strength to ( e − u ) states are ruled out at the 95% confidence level for masses below 168 GeV for left-handed couplings and below 176 GeV for right-handed couplings.