Mass Limit for the Lightest Neutralino

Abstract

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 sneutrinos is presented in the framework of SUSY grand unified theories; a massless neutralino is allowed only for a narrow range of $\tan\beta$, $\mu$, and the scalar mass parameter $m_0$. Finally, by including Higgs mass constraints and requiring that radiative electroweak symmetry breaking occur, more stringent bounds on $M_\chi$ as a function of $\tan\beta$ are derived.