We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ($tilde{t}_1$) in $pbar{p}$ collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider corresponding to an integ
rated 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 ($tilde{ u}$), 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 ($M_{tilde{t}_1}$,$M_{tilde{ u}}$) mass plane.
