Search for Unstable Heavy and Excited Leptons at LEP2

TL;DR

This study searches for unstable heavy and excited leptons at LEP2 energies using OPAL data, setting new mass limits and coupling constraints due to the absence of observed signals.

Contribution

It provides the first experimental mass limits and coupling constraints for unstable heavy and excited leptons at LEP2 energies.

Findings

No evidence for new heavy or excited leptons was observed.

Lower mass limits were established for unstable heavy and excited leptons.

Upper limits on the coupling to the compositeness scale were determined for excited leptons.

Abstract

Searches for unstable neutral and charged heavy leptons, N and L+-, and for excited states of neutral and charged leptons, nu*, e*, mu*, and tau*, have been performed in e+e- collisions using data collected by the OPAL detector at LEP. The data analysed correspond to an integrated luminosity of about 58pb-1 at a centre-of-mass energy of 183GeV, and about 10pb-1 each at 161GeV and 172GeV. No evidence for new particles was found. Lower limits on the masses of unstable heavy and excited leptons are derived. From the analysis of charged-current, neutral-current, and photonic decays of singly produced excited leptons, upper limits are determined for the ratio of the coupling to the compositeness scale, f/Lambda, for masses up to the kinematic limit. For excited leptons, the limits are established independently of the relative values of the coupling constants f and f'.