  A search for pair production of the lightest supersymmetric partner of the
top quark is performed in the lepton+jets channel using 0.9 fb-1 of data
collected by the D0 experiment. Kinematic differences between scalar top quark
pair production and the dominant top quark pair production background are used
to separate the two processes. First limits from Run II of the Fermilab
Tevatron Collider for the scalar top quark decaying to a chargino and a b quark
are obtained for scalar top quark masses of 130-190 GeV and chargino masses of
90-150 GeV.
