Search for Flavor Changing Neutral Currents in Top Quark Decays using a Two-Leptons + Tracks selection

A search for flavor-changing neutral currents in top quark decays is described. Data collected at a center- of-mass energy of $sqrt{s}$ = 7 TeV during 2011 corresponding to an integrated luminosity of 2.1 fb$^{-1}$ are used. A cut-based analysis is used on top quark pair production events, where one top quark is assumed to follow the dominant Standard Model decay $t ightarrow Wb$, and the other the flavor changing neutral current decay $t ightarrow Zq$. Only the decays of the Z-boson to charged leptons and leptonic W-boson decays are considered signal. The search uses an event selection with two identified leptons (electrons and/or muons) and one lepton selected via inner-detector track requirements only (track lepton). Backgrounds to the search are evaluated using almost entirely data-driven techniques. An orthogonal channel, with three identified leptons is also described, and used in the final result. No significant excess is observed in the signal region. An upper limit on the $t ightarrow qZ$ branching ratio of BR($t ightarrow Zq$) <0.73% is set at the 95% confidence level, compatible with the expected limit.