Search for admixture of scalar top quarks in the tt¯ lepton + jets final state at s=1.96 TeV

A search for pair production of the lightest supersymmetric partner of the top quark, t˜1, is performed in the lepton + jets channel using 0.9 fb−1 of data collected by the DØ experiment. Kinematic differences between t˜1t˜¯1 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 (t˜1→χ˜1+b) are obtained for scalar top quark masses of 130-190 GeV and chargino masses of 90-150 GeV.