Search for chargino and neutralino production at $\sqrt{s} = 181$–$184$ GeV at LEP

The OPAL Collaboration: G. Abbiendi - et al.

doi:doi:10.1007/s100529901059

2022 Impact factor 4.4

Particles and Fields

Eur. Phys. J. C 8, 255-272
DOI 10.1007/s100529901059

Search for chargino and neutralino production at $\sqrt{s} = 181$ -184 GeV at LEP

The OPAL Collaboration
G.Abbiendi² - et al.

²Dipartimento di Fisica dell' Università di Bologna and INFN, I-40126 Bologna, Italy

Received: 19 August 1998 / Published online: 11 March 1999

Abstract
A search for charginos and neutralinos, predicted by supersymmetric theories, has been performed using a data sample of 57 pb^-1 at centre-of-mass energies of 181-184 GeV taken with the OPAL detector at LEP. No evidence for chargino or neutralino production has been found. Upper limits on chargino and neutralino pair production ( $\tilde{\chi}^+_1 \tilde{\chi}^-_1$ , $\tilde{\chi}^0_1 \tilde{\chi}^0_2$ ) cross-sections are obtained as a function of the chargino mass ( $m_{\tilde{\chi}^\pm_1}$ ), the lightest neutralino mass ( $m_{\tilde{\chi}^0_1}$ )and the second lightest neutralino mass ( $m_{\tilde{\chi}^0_2}$ ). For large chargino masses the limits have been improved with respect to the previous analyses at lower centre-of-mass energies. Exclusion regions at 95% confidence level (C.L.) of parameters of the Constrained Minimal Supersymmetric Standard Model are determined for the case of a large universal scalar mass, m₀, implying heavy scalar fermions, and for the case of a small m₀ resulting in light scalar fermions and giving the worst-case limits. Within this framework and for $m_{\tilde{\chi}^\pm_1} - m_{\tilde{\chi}^0_1} \geq 5$ GeV the 95% C.L. lower limits on $m_{\tilde{\chi}^\pm_1}$ for m₀=500 GeV are 90.0 and 90.2 GeV for $\tan \beta = 1.5$ and 35 respectively. These limits for all m₀ (the worst-case) are 69.1 and 65.2 GeV for $\tan \beta = 1.5$ and 35 respectively. Exclusion regions are also presented for neutralino masses, including an absolute lower limit at 95% C.L. for the mass of the lightest neutralino of 30.1 GeV for m₀ = 500 GeV (24.2 GeV for all m₀), with implications for experimental searches for the lightest neutralino as a dark matter candidate.