Search for Nearly Mass-Degenerate Charginos and Neutralinos at LEP

TL;DR

This paper reports a search for nearly mass-degenerate charginos and neutralinos at LEP, finding no evidence of such particles and setting new limits on their masses and production cross-sections within supersymmetric models.

Contribution

The study introduces a novel search strategy using high-energy photon events to detect nearly mass-degenerate charginos and neutralinos at LEP, providing new exclusion limits.

Findings

No significant excess observed over Standard Model predictions.

Upper limits set on chargino pair-production cross-section.

Lower mass limits established for charginos in supersymmetric models.

Abstract

A search was performed for charginos with masses close to the mass of the lightest neutralino in e+e- collisions at centre-of-mass energies of 189-209 GeV recorded by the OPAL detector at LEP. Events were selected if they had an observed high-energy photon from initial state radiation, reducing the dominant background from two-photon scattering to a negligible level. No significant excess over Standard Model expectations has been observed in the analysed data set corresponding to an integrated luminosity of 570pb-1. Upper limits were derived on the chargino pair-productin cross-section, and lower limits on the chargino mass were derived in the context of the Minimal Supersymmetric Extension of the Standard Model for the gravity and anomaly mediated Supersymmetry breaking scenarios.