Update of the search for charginos nearly mass-degenerate with the lightest neutralino

TL;DR

This study updates the search for nearly mass-degenerate charginos using 1998 DELPHI data at 189 GeV, setting new lower mass limits and excluding certain parameter regions.

Contribution

It provides the first elta M limit on chargino mass for near-degenerate scenarios, extending previous searches with new data and analysis.

Findings

No excess events observed over Standard Model expectations.

Lower mass limit for charginos is 62.4 GeV/c^2 in the higgsino scenario.

Excludes chargino masses below 59.8 GeV/c^2 for large sfermion masses.

Abstract

The data collected by DELPHI in 1998 at the centre-of-mass energy of 189 GeV have been used to update the search for charginos nearly mass-degenerate with the lightest supersymmetric particle, which is assumed to be the lightest neutralino. Mass differences below \Delta M = 3 GeV/c^2 are considered. No excess of events with respect to the Standard Model expectation has been observed, and exclusions in the plane of \Delta M versus chargino mass are given. The new \Delta M independent lower limit on the mass of the chargino is 62.4 GeV/c^2 in the higgsino scenario (which includes the gaugino mass unification scenario), if all sfermions are heavier than the lightest chargino. In the approximation of large sfermion masses the limit is 59.8 GeV/c^2, independently of the field content.