Absolute mass lower limit for the lightest neutralino in the MSSM from e+e- data up to sqrt(s) = 209GeV

Charginos and neutralinos are searched for in the data collected by the ALEPH experiment at LEP for centre-of-mass energies up to 209\,GeV. The negative result of these searches is combined with those from searches for sleptons, squarks and Higgs bosons to derive an absolute lower limit of 41.6\,$\Gcs$ on the mass of the lightest supersymmetric particle, assumed to be the lightest neutralino. This limit, obtained in the framework of the MSSM with R-parity conservation and with gaugino and sfermion mass unification at the GUT scale, is shown to be valid for any mixing angle in the stau sector for $\tanb > 1.8$. Within the more constrained framework of minimal supergravity, the limit on the lightest supersymmetric particle is set to 50\,$\Gcs$.