We have searched for direct production of scalar top quarks at the Collider Detector at Fermilab in $88{\mathrm{pb}}^{-1\mathrm{}}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.8\mathrm{}\mathrm{TeV}$. We assume the scalar top quark decays into either a bottom quark and a chargino or a bottom quark, a lepton, and a scalar neutrino. The event signature for both decay scenarios is a lepton, missing transverse energy, and at least two $b$-quark jets. For a chargino mass of $90\mathrm{GeV}{/c}^2$ and scalar neutrino masses of at least $40\mathrm{GeV}{/c}^2$, we find no evidence for scalar top production and present upper limits on the production cross section in both decay scenarios.

• Received 16 November 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.5273