Scalar quark searches in e^+e^- collisions at sqrt{s} = 181-184 GeV

Abstract

Searches for scalar top, scalar bottom and degenerate scalar quarks have been performed with data collected with the ALEPH detector at LEP. The data sample consists of 57 pb^-1 taken at sqrt{s} = 181-184 GeV. No evidence for scalar top, scalar bottom or degenerate scalar quarks was found in the channels tilde{t} --> c chi, tilde{t} --> b l snu, tilde{b} --> b chi, and tilde{q} --> q chi. From the channel tilde{t} --> c chi a limit of 74 GeV/c^2 has been set on the scalar top quark mass, independent of the mixing angle. This limit assumes a mass difference between the stop and the chi in the range 10-40 GeV/c^2. From the channel tilde{t} --> b l snu the mixing-angle-independent scalar top limit is 82 GeV/c^2, assuming m_stop - m_snu > 10 GeV/c^2. From the channel tilde{b} --> b chi a limit of 79 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 for m_sbottom - m_chi > 10 GeV/c^2. From the channel tilde{q} --> q chi a limit of 87 GeV/c^2 has been set on the mass of supersymmetric partners of light quarks, assuming five degenerate flavours and the production of both ``left-handed'' and ``right-handed'' squarks. This limit is valid for m_squark - m_chi > 5 GeV/c^2.