Searches for scalar top and scalar bottom quarks at LEP2

Abstract Searches for scalar top and bottom quarkshave been performed with data collected by the ALEPHdetector at LEP. The data sample consists of 21.7 pb −1 taken at s = 161, 170 , and 5.7 pb −1 taken at s = 130 and 136 GeV . No evidence for scalar top quarksor scalar bottom quarkswas found in the channels t → cχ, t → bl ν , and b → bχ. For the channel t → cχ a limit of 67 GeV/ c 2 has been set on the scalar top quarkmass, independent of the mixing angle between the supersymmetric partners of the left and right-handed states of the top quark. This limit assumes a mass difference between the t and the χ of at least 10 GeV/ c 2 . For the channel t → bl ν the mixing-angle independent scalar top limit is 70 GeV/ c 2 , assuming a mass difference between the t and the ν of at least 10 GeV/ c 2 . For the channel b → bχ, a limit of 73 GeV/ c 2 has been set on the mass of the supersymmetric partner of the left-handed state of the bottom quark. This limit is valid if the mass difference between the b and the χ is at least 10 GeV/ c 2 .