Search For Lepton-Flavor Violation In E(+)P Collisions At Desy Hera

A search has been made for lepton-flavor-violating interactions of the type e(+)p-->lX, where l denotes a mu or tau with high transverse momentum, at a center-of-mass energy roots of 300 GeV with an integrated luminosity of 47.7 pb(-1) using the ZEUS detector at HERA. No evidence was found for lepton-flavor violation and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below roots, limits are set on lambda(eq1) rootbeta(lq), where lambda(eq1) is the coupling of the LQ to an electron and a first-generation quark q(1) and beta(lq) is the branching ratio of the LQ to l and a quark. For LQ masses exceeding roots, limits are set on the four-fermion contact-interaction term lambda(eqalpha) lambda(lqbeta)/M-LQ(2) for leptoquarks that couple to an electron and a quark q(alpha) and also to l and a quark q(beta). Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in R-parity-violating supersymmetric models. In some cases involving heavy quarks and especially for l = tau, the ZEUS limits are the most stringent published to date.