Search for composite and exotic fermions at LEP 2

TL;DR

This paper reports a search for heavy and exotic fermions at LEP 2, setting mass limits and coupling constraints based on data from electron-positron collisions at energies around 161-183 GeV.

Contribution

It provides new experimental mass limits and coupling constraints for composite and exotic fermions using LEP 2 data, covering various fermion types and production modes.

Findings

Mass limits between 70 and 90 GeV/c^2 for pair-produced leptons

Upper limits on coupling ratios for excited fermions and quarks

No evidence found for the existence of the targeted exotic fermions

Abstract

A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172 GeV and 161 GeV. The search for pair-produced new leptons establishes 95% confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2, depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio of the coupling of the excited fermion