Search for pair production of the scalar top quark in muon+tau final states

We present a search for the pair production of scalar top quarks (${\tilde{t}}_1$), the lightest supersymmetric partners of the top quarks, in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV, using data corresponding to an integrated luminosity of {7.3 $f{b}^{-1}$} collected with the \dzero experiment at the Fermilab Tevatron Collider. Each scalar top quark is assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tilde{\nu }$). We investigate final states arising from $\tilde{t}{1} \bar{\tilde{t}{1}} \rightarrow b\bar{b}\mu\tau \tilde{\nu} \tilde{\nu}$and$\tilde{t}{1} \bar{\tilde{t}{1}} \rightarrow b\bar{b}\tau\tau \tilde{\nu} \tilde{\nu}$. With no significant excess of events observed above the background expected from the standard model, we set exclusion limits on this production process in the ($m_{{\tilde{t}}_1}$,$m_{\tilde{\nu }}$) plane.