Neutralino mass bounds at the upgraded LEP collider

Abstract

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 ($\tan\beta > 2$).