Searches for excited fermions in ep collisions at HERA

TL;DR

This paper reports on searches for excited fermions in electron-proton collisions at HERA, finding no evidence and setting limits on their couplings for masses below 250 GeV.

Contribution

First comprehensive search for excited electrons, quarks, and neutrinos at HERA, establishing new limits on their existence and couplings.

Findings

No evidence for excited fermions was observed.

Limits on couplings were set for masses below 250 GeV.

The study covers multiple decay channels for each fermion type.

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*->egamma, e*->eZ and e*->nuW. Excited quarks have been sought via the decays q*->qgamma and q*->qW. A search for excited neutrinos decaying via nu*->nugamma, nu*->nuZ and nu*->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 below 250 GeV.