A search for electron and neutrino composteness in ep collisions at HERA

The observation of excited states of the fundamental fermions would be a clear signal that these particles are composite rather than elementary. Heavy excited states of electrons have been searched for in e+p collisions at a center-of-mass energy of 300 GeV with the ZEUS detector at HERA using a data set corresponding to an integrated luminosity of 38.4 pb-1. A signal for an excited electron was sought via the decay modes e*→eγ, e*→eZ and e*→νW. A search for excited neutrinos decaying via ν*→νγ using the recent e-p collision data at 318 GeV center-of-mass energy corresponding to an integrated luminosity of 16.7 pb-1 has also been performed. No evidence was found for such states and limits on the characteristic couplings are derived. (orig.)