Search for Nearly Mass Degenerate Charginos and Neutralinos in e+e- Collisions

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 570 pb−1 . Upper limits were derived on the chargino pair-production 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. Studies concerning searchesfor nearly mass degenerate charginos and neutralinos at the next generation Linear Collider project, TESLA, are presented. A matter of particular interest was the influence of beam-induced background enviroment on the detector design and performance.