Search for charginos nearly mass degenerate with the lightest neutralino in e+e- collisions at centre-of-mass energies up to 209GeV

TL;DR

This paper reports a search for nearly mass-degenerate charginos and neutralinos at LEP energies, using initial state radiation photons to detect chargino pairs with minimal visible decay products, setting a lower mass limit of 88 GeV.

Contribution

It introduces a novel detection method for nearly mass-degenerate charginos using initial state radiation photons at LEP energies, extending previous search capabilities.

Findings

No excess events observed beyond Standard Model expectations.

A lower chargino mass limit of 88 GeV at 95% confidence level was established.

Results are combined with other searches to improve constraints.

Abstract

A search for charginos nearly mass degenerate with the lightest neutralino is performed with the data collected by the ALEPH detector at LEP, at centre-of-mass energies between 189 and 209 GeV, corresponding to an integrated luminosity of 628 pb-1. The analysis is based on the detection of isolated and energetic initial state radiation photons, produced in association with chargino pairs whose decay products have little visible energy. The number of candidate events observed is in agreement with that expected from Standard Model background sources. These results are combined with those of other direct searches for charginos, and a lower limit of 88 GeV/c2 at 95 % confidence level is derived for the chargino mass in the case of heavy sfermions, irrespective of the chargino-neutralino mass difference.