2018 Impact factor 4.843
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.Abbiendi 2 - et al.

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

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

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.

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