Search for Chargino and Neutralino Production at sqrt{s} = 170 and 172 GeV at LEP

TL;DR

This study searched for supersymmetric particles chargino and neutralino at LEP energies of 170 and 172 GeV, setting new lower mass limits and excluding certain parameter regions within the MSSM framework.

Contribution

It provides the first combined limits on chargino and neutralino masses at these energies, extending previous bounds and constraining MSSM parameters.

Findings

No evidence for chargino or neutralino production was observed.

Lower mass limits for the lightest chargino are 84.5 GeV and 65.7 GeV under different assumptions.

Lower mass limits for the lightest neutralino are 24.7 GeV and 13.3 GeV depending on m_0.

Abstract

A search for charginos and neutralinos, predicted by supersymmetric theories, has been performed using a data sample of 10.3 pb^-1 at centre-of-mass energies of sqrt(s) = 170 and 172 GeV with the OPAL detector at LEP. No evidence for these particles has been found. The results are combined with those from previous OPAL chargino and neutralino searches at lower energies to obtain limits. Exclusion regions at 95% C.L. of parameters of the Minimal Supersymmetric Standard Model are determined. Within this framework, for tan(beta) >= 1.0, lower mass limits are placed on the lightest chargino and the three lightest neutralinos. The 95% C.L. lower mass limit on the lightest chargino, assuming that it is heavier than the lightest neutralino by more than 10 GeV, is 84.5 GeV for the case of a large universal scalar mass (m_0 > ~1 TeV) and 65.7 GeV for the smallest m_0 compatible with current limits on the sneutrino and slepton masses. The lower limit on the lightest neutralino mass at 95% C.L. for tan(beta) >= 1.0 is 24.7 GeV for m_0 = 1 TeV and 13.3 GeV for the minimum m_0 scenario. These mass limits are higher for increasing values of tan(beta). The interpretation of the limits in terms of gluino and scalar quark mass limits is also given.