Search for Unstable Heavy and Excited Leptons in e^+e^- Collisions at sqrt{s} = 170-172 GeV

TL;DR

This study searched for unstable heavy and excited leptons in electron-positron collisions at 170-172 GeV energies using the OPAL detector, finding no evidence but setting mass and coupling limits.

Contribution

It provides the first experimental limits on the masses and couplings of heavy and excited leptons at these energies.

Findings

No evidence for heavy or excited leptons was observed.

Lower mass limits were established for pair-produced unstable heavy leptons.

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

Abstract

We have searched for unstable neutral and charged heavy leptons, N and L^+/-, and for excited states of neutral and charged leptons, nu*, e*, mu* and tau*, in e^+e^- collisions at centre-of-mass energies of 170 and 172 GeV using the OPAL detector at LEP. No evidence for their existence was found. From the analysis of charged-current decays of pair-produced unstable heavy leptons, and of charged-current and photonic decays of pair-produced excited leptons, lower limits on their masses are derived. From the analysis of charged-current and photonic decays of singly-produced excited leptons, upper limits on the ratio of the coupling to the compositeness scale, f/Lambda, are determined for masses up to the kinematic limit.