Search for Supersymmetric Particles in e+e− Collisions at √s up to 202 GeV and Mass Limit for the Lightest Neutralino

Searches for pair productionof squarks, sleptons, charginosand neutralinosare performed with the data collected by the ALEPHdetector at LEP at centre-of-mass energies from 188.6 to 201.6 GeV. No evidence for any such signals is observed in a total integrated luminosity of about 410 pb−1. The negative results of the searches are translated into exclusion domains in the space of the relevant MSSM parameters, which improve significantly on the constraints set previously. Under the assumptions of gauginoand sfermionmass unification, these results allow a 95% C.L. lower limit of 37 GeV/c2 to be set on the mass of the lightest neutralinofor any tanβ and sfermionmass. Additional constraints in the MSSM parameter space are derived from the negative results of ALEPHsearches for Higgs bosons. The results are also interpreted in the framework of minimal supergravity.