Search for lepton-flavor violation in e + p collisions at HERA ZEUS Collaboration

A search has been made for lepton-flavor-violating interactions of the type ep → lX, where l denotes a μ or τ with high transverse momentum, at a center-of-mass energy, √ s, of 300 GeV with an integrated luminosity of 47.7 pb 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 √ s, limits are set on λeq 1 √ βlq, where λeq 1 is the coupling of the LQ to an electron and a first-generation quark q 1 and βlq is the branching ratio of the LQ to l and a quark. For LQ masses exceeding √ s, limits are set on the four-fermion contact-interaction term λeqαλlqβ/M 2 LQ for leptoquarks that couple to an electron and a quark qα and also to l and a quark qβ. 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 = τ , the ZEUS limits are the most stringent published to date. The ZEUS Collaboration S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Yoshida Argonne National Laboratory, Argonne, Illinois 60439-4815 M.C.K. Mattingly Andrews University, Berrien Springs, Michigan 49104-0380 P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Levi, A. Margotti, T. Massam, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi University and INFN Bologna, Bologna, Italy G. Aghuzumtsyan, D. Bartsch, I. Brock, J. Crittenden, S. Goers, H. Hartmann, E. Hilger, P. Irrgang, H.-P. Jakob, A. Kappes, U.F. Katz, R. Kerger, O. Kind, E. Paul, J. Rautenberg, R. Renner, H. Schnurbusch, A. Stifutkin, J. Tandler, K.C. Voss, A. Weber, H. Wessoleck Physikalisches Institut der Universität Bonn, Bonn, Germany D.S. Bailey, N.H. Brook, J.E. Cole, B. Foster, G.P. Heath, H.F. Heath, S. Robins, E. Rodrigues, J. Scott, R.J. Tapper, M. Wing H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom M. Capua, A. Mastroberardino, M. Schioppa, G. Susinno Calabria University, Physics Department and INFN, Cosenza, Italy H.Y. Jeoung, J.Y. Kim, J.H. Lee, I.T. Lim, K.J. Ma, M.Y. Pac Chonnam National University, Kwangju, Korea A. Caldwell, M. Helbich, X. Liu, B. Mellado, S. Paganis, W.B. Schmidke, F. Sciulli Nevis Laboratories, Columbia University, Irvington on Hudson, New York 10027 J. Chwastowski, A. Eskreys, J. Figiel, K. Olkiewicz, M.B. Przybycień, P. Stopa, L. Zawiejski Institute of Nuclear Physics, Cracow, Poland B. Bednarek, I. Grabowska-Bold, K. Jeleń, D. Kisielewska, A.M. Kowal, M. Kowal, T. Kowalski, B. Mindur, M. Przybycień, E. Rulikowska-Zarȩbska, L. Suszycki, D. Szuba, J. Szuba Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy, Cracow, Poland A. Kotański, W. S lomiński Department of Physics, Jagellonian University, Cracow, Poland