Searches for excited fermions in ep collisions at HERA

Searches in ep collisions for heavy excited fermions have been performed with the ZEUS detector at HERA. Excited states of electrons and quarks have been searched for in ep collisions at a centre-of-mass energy of 300GeV using an integrated luminosity of 47.7 pb. Excited electrons have been sought via the decays e → eγ, e → eZ and e → νW . Excited quarks have been sought via the decays q → qγ and q → qW . A search for excited neutrinos decaying via ν → νγ, ν → νZ and ν → eW is presented using ep collisions at 318GeV centre-of-mass energy, corresponding to an integrated luminosity of 16.7 pb. No evidence for any excited fermion is found, and limits on the characteristic couplings are derived for masses . 250GeV. 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 n 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 e G. Aghuzumtsyan, I. Brock, S. Goers, H. Hartmann, E. Hilger, P. Irrgang, H.-P. Jakob, A. Kappes, U.F. Katz, R. Kerger, O. Kind, E. Paul, J. Rautenberg, H. Schnurbusch, A. Stifutkin, J. Tandler, K.C. Voss, A. Weber, H. Wieber Physikalisches Institut der Universität Bonn, Bonn, Germany b 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 M. Capua, A. Mastroberardino, M. Schioppa, G. Susinno Calabria University, Physics Department and INFN, Cosenza, Italy e H.Y. Jeoung, J.Y. Kim, J.H. Lee, I.T. Lim, K.J. Ma, M.Y. Pac Chonnam National University, Kwangju, Korea g 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 o J. Chwastowski, A. Eskreys, J. Figiel, K. Klimek, K. Olkiewicz, M.B. Przybycień, P. Stopa, L. Zawiejski Institute of Nuclear Physics, Cracow, Poland i 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 i A. Kotański Department of Physics, Jagellonian University, Cracow, Poland