Abstract
ATLAS results are presented on a search for flavor-changing neutral currents (FCNC) in top quark decays at the LHC. Events are searched for where a pair of top quarks is produced and one decays through the Standard Model $t \rightarrow Wb$ mode while the other decays through the FCNC mode $t \rightarrow qZ$. Leptonic final states are used in which both the $W$- and $Z$-bosons decay leptonically, yielding final states with three leptons and two jets. The observed events are consistent with the expected backgrounds from Drell-Yan and diboson production and a limit on the FCNC branching ratio of top quarks to $qZ$ is set.
Highlights
If anomalous top-quark couplings exist, this would affect production and/or decay processes at hadron colliders, such as the LHC
Events are searched for where a pair of top quarks is produced and one decays through the Standard Model t → Wb mode while the other decays through the flavor-changing neutral currents (FCNC) mode t → qZ
These decays are highly suppressed in the Standard Model (SM), observation of such a decay would be suggestive of new physics
Summary
If anomalous top-quark couplings exist, this would affect production and/or decay processes at hadron colliders, such as the LHC. A rare top-quark decay is that which occurs via FCNC. These decays are highly suppressed in the Standard Model (SM), observation of such a decay would be suggestive of new physics. A search was done for ttpairs with one top quark decaying through flavor-changing neutral currents (t → qZ) and the other through the SM dominant mode (t → bW). The leptonic decays of the W- and the Z-bosons are considered signal. The main background sources are ZZ and WZ events, which include three charged leptons in the final state, and were estimated with Monte Carlo (MC) simulation. Backgrounds with one, two, or three fake leptons, were estimated by data-driven (DD) methods [1]
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