Searches for excited fermions in ep collisions at HERA

Abstract 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 e + p collisions at a centre-of-mass energy of 300 GeV using an integrated luminosity of 47.7 pb −1 . 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 e − p collisions at 318 GeV centre-of-mass energy, corresponding to an integrated luminosity of 16.7 pb −1 . No evidence for any excited fermion is found, and limits on the characteristic couplings are derived for masses ≲250 GeV.