Searches for Scalar Top and Scalar Bottom Quarks at LEP2

TL;DR

This paper reports on searches for scalar top and bottom quarks at LEP2, setting mass limits in various decay channels with no evidence of their existence within the analyzed data.

Contribution

The study provides new mass limits for scalar top and bottom quarks at LEP2, independent of mixing angles, based on analysis of specific decay channels and data sets.

Findings

No evidence for scalar top or bottom quarks was found.

Mass limits of 67-73 GeV/c^2 were set for different decay channels.

Limits are valid assuming at least 10 GeV/c^2 mass difference.

Abstract

Searches for scalar top and bottom quarks have been performed with data collected by the ALEPH detector at LEP. The data sample consists of 21.7 pb^-1 taken at sqrt{s} = 161, 170, and 172~GeV and 5.7 pb^-1 taken at sqrt{s} = 130 and 136~GeV. No evidence for scalar top quarks or scalar bottom quarks was found in the channels stop --> c chi, stop --> b l snu, and sbottom --> b chi. For the channel stop --> c chi a limit of 67 GeV/c^2 has been set on the scalar top quark mass, 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 stop and the chi of at least 10 GeV/c^2. For the channel stop --> b l snu the mixing-angle independent scalar top limit is 70 GeV/c^2, assuming a mass difference between the stop and the snu of at least 10 GeV/c^2. For the channel sbottom --> b chi, 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 sbottom and the chi is at least 10 GeV/c^2.