Searches for sleptons and squarks in e+e− collisions at 189 GeV

Abstract The data collected at a centre-of-mass energy of 188.6 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 173.6 pb −1 , are analysed in a search for the scalar partners of quarks and leptons predicted in supersymmetric models. No evidence for any such particles was found in the decay channels l →lχ , t → c χ , t → b l ν , b → b χ , and q → q χ . Improved mass lower limits have been obtained in the framework of the Minimal Supersymmetric Standard Model.