Search for lepton flavor violation in $ep$ collisions at 300-GeV center-of-mass energy

Using the ZEUS detector at the HERAelectron-proton collider, we have searched for lepton flavorviolation in ep collisions at a center-of-mass energy (root s) of 300 GeV. Events of the type e + p --> l + X with a final-state leptonof high transverse momentum, l = mu or tau, were sought. No evidence was found for lepton flavorviolation in the combined 1993 and 1994 data samples, for which the integrated luminosities were 0.84 pb(-1) for e(-)p collisions and 2.94 pb(-1) for e(+)p collisions. Limits on coupling vs. mass are provided for leptoquarksand R-parityviolating squarks, For flavorviolating couplings of electromagnetic strength, we set 95% confidence level lower limits on leptoquarkmasses between 207 GeV and 272 GeV, depending on the leptoquarkspecies and final-state lepton. For leptoquark,masses larger than 300 GeV, limits on flavor-changing couplings are determined, many of which supersede prior limits from rare decay processes.