June 10, 1996
Assuming that no supersymmetric signature will be found at the upgraded LEP collider we derive lower bounds on the masses of the four neutralinos $\tilde{\chi}_i^0$ in the Minimal Supersymmetric Standard Model (MSSM). We consider the recently published results from the search for the light chargino $\tilde{\chi}^\pm_1$ and the next-to-lightest neutralino $\tilde{\chi}^0_2$ at LEP1.5 and study the consequences of possible future lower $\tilde{\chi}^\pm_1$ and $\tilde{\chi}^0_2$ mass limits between 65 and 95 GeV. For a chargino mass bound of 66.8 GeV at LEP1.5, a massless neutralino is not excluded for $\tan\beta < 1.2$. If either $\tan\beta > 2.3$ or the gluino mass $m_{\tilde{g}} > 160$ GeV, we find $m_{\tilde{\chi}_1^0} > 28$ GeV. A possible chargino bound $m_{\tilde{\chi}_1^\pm} > 95$ GeV at LEP2 would raise this bound to 31 GeV (for all $\tan\beta$) or 44 GeV ($\tan\beta > 2$).
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Indirect limits on the mass of the lightest neutralino are derived from the results of searches for charginos, neutralinos, and sleptons performed with data taken by the ALEPH Collaboration at centre-of-mass energies near the Z peak and at 130 and 136 GeV. Within the context of the Minimal Supersymmetric Standard Model and when $M_{\tilde\nu}\ge 200$ GeV/c^2, the bound $M_\chi>12.8$ GeV/c^2 at the 95\% confidence level applies for any $\tan\beta$. The impact of lighter sneutr...
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Within the Minimal Supersymmetric Standard Model (MSSM) we systematically investigate the bounds on the mass of the lightest neutralino. We allow for non-universal gaugino masses and thus even consider massless neutralinos, while assuming in general that R-parity is conserved. Our main focus are laboratory constraints. We consider collider data, precision observables, and also rare meson decays to very light neutralinos. We then discuss the astrophysical and cosmological impl...
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We show that LEPII will either discover charginos and neutralinos, or enable a very stringent upper limit to be placed on $\tan \beta$ as a function of the gluino mass. The only assumption we make is the existence of some unified model which breaks down to the minimal supersymmetric standard model below the unification scale. In such a framework we discuss how the discovery of a chargino at LEPII and the measurement of its mass and production cross-section, together with the ...
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