Search for Chargino and Neutralino Production at sqrt{s} = 189 GeV at LEP

TL;DR

This paper reports a search for supersymmetric particles, charginos and neutralinos, at LEP with no evidence found, setting new lower mass limits within the MSSM framework based on 182.1 pb-1 of data at 189 GeV.

Contribution

First search at LEP for charginos and neutralinos at 189 GeV, establishing new mass limits within the MSSM framework with detailed parameter assumptions.

Findings

No evidence for chargino or neutralino production.

Lower mass limits: chargino > 93.6 GeV (tanβ=1.5), > 94.1 GeV (tanβ=35).

Neutralino > 32.8 GeV for all m_0.

Abstract

A search for charginos and neutralinos, predicted by supersymmetric theories, is performed using a data sample of 182.1 pb-1 taken at a centre-of-mass energy of 189 GeV with the OPAL detector at LEP. No evidence for chargino or neutralino production is found. Upper limits on chargino and neutralino pair production cross-sections are obtained as a function of the chargino mass, the lightest neutralino mass and the second lightest neutralino mass. Within the Constrained Minimal Supersymmetric Standard Model framework, and for a chargino - neutralino mass difference of more than 5 GeV, the 95% confidence level lower limits on the chargino mass are 93.6 GeV for tan{beta} = 1.5 and 94.1 GeV for tan{beta} = 35. These limits are obtained assuming a universal scalar mass m_0 > 500 GeV. The corresponding limits for all m_0 are 78.0 and 71.7 GeV. The 95% confidence level lower limits on the lightest neutralino mass, valid for any value of tan{beta} are 32.8 GeV for m_0 > 500 GeV and 31.6 GeV for all m_0.