  We report the result of a search for the pair production of the lightest
supersymmetric partner of the top quark ($\tilde{t}_1$) in $p\bar{p}$
collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron
collider corresponding to an integrated luminosity of 5.4 fb$^{-1}$. The scalar
top quarks are assumed to decay into a $b$ quark, a charged lepton, and a
scalar neutrino ($\tilde{\nu}$), and the search is performed in the electron
plus muon final state. No significant excess of events above the standard model
prediction is detected, and improved exclusion limits at the 95% C.L. are set
in the the ($M_{\tilde{t}_1}$,$M_{\tilde{\nu}}$) mass plane.
