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Abstract
Abstract.
A search for lepton-flavor-violating interactions \(e p \to \mu X \) and \(e p\to \tau X \) has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity of \(130 \text{pb}^{-1}\). The data were taken at center-of-mass energies, \(\sqrt{s}\), of 300 and \(318 \text{Ge}\;\text{V\/}\). No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below \(\sqrt{s}\), limits were set on \(\lambda_{eq_1} \sqrt{\beta_{\ell q}}\), where \(\lambda_{eq_1}\) is the coupling of the LQ to an electron and a first-generation quark q1, and \(\beta_{\ell q}\) is the branching ratio of the LQ to the final-state lepton \(\ell\) (μ or \(\tau\)) and a quark q. For LQ masses much larger than \(\sqrt{s}\), limits were set on the four-fermion interaction term \(\lambda_{e q_\alpha} \lambda_{\ell q_\beta} / M_{\mathrm{LQ}}^2\) for LQs that couple to an electron and a quark \(q_\alpha\) and to a lepton \(\ell\) and a quark \(q_\beta\), where \(\alpha\) and \(\beta\) 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 \(e p\to \tau X \), the ZEUS limits are the most stringent to date.