Search for lepton-flavor violation at HERA
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A search for lepton-flavor-violating interactions ep X and ep X has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity of 130 pb-1. The data were taken at center-of-mass energies, s, of 300 and 318 GeV. No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below s, limits were set on eq1 q, where eq1 is the coupling of the LQ to an electron and a first-generation quark q1, and q is the branching ratio of the LQ to the final-state lepton ( or ) and a quark q. For LQ masses much larger than s, limits were set on the four-fermion interaction term eq q/MLQ2 for LQs that couple to an electron and a quark qalpha and to a lepton and a quark q beta, where and are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in R-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the process ep X, the ZEUS limits are the most stringent to date. Springer-Verlag.
