Abstract
A search is performed for flavour-changing neutral currents in the decay of a top quark to an up-type ($c, u$) quark and a Higgs boson, where the Higgs boson decays to two photons. The proton-proton collision data set used corresponds to 4.7 fb$^{-1}$ at $\sqrt{s}$ = 7 \tev\ and 20.3 fb$^{-1}$ at $\sqrt{s}$ = 8 \tev\ collected by the ATLAS experiment at the LHC. Top quark pair events are searched for in which one top quark decays to $qH$ and the other decays to $bW$. Both the hadronic and the leptonic decay modes of the $W$ boson are used. No significant signal is observed and an upper limit is set on the $t\rightarrow qH$ branching ratio of 0.79% at the 95% confidence level. The corresponding limit on the $tqH$ coupling combination $\sqrt{\lambda_{tcH}^{2} + \lambda_{tuH}^{2}}$ is 0.17.
Highlights
Detector and data setThe ATLAS detector [41] consists of an inner tracking detector (ID) surrounded by a superconducting solenoid providing a 2 T magnetic field, electromagnetic and hadronic calorimeters, and a muon spectrometer
Background estimate for the hadronic channelDue to low statistics the data distribution in the control region (CR) alone cannot be used to constrain the background shape
As the analysis is sensitive to the t → uH and t → cH modes, the limit obtained on the couplings can be written as λ2tcH + λ2tuH < 0.17, with an expectation of 0.14
Summary
The ATLAS detector [41] consists of an inner tracking detector (ID) surrounded by a superconducting solenoid providing a 2 T magnetic field, electromagnetic and hadronic calorimeters, and a muon spectrometer. The muon spectrometer consists of precision (|η| < 2.7) and trigger (|η| < 2.4) chambers embedded in a toroidal magnet system which surrounds the hadronic calorimeter. This analysis uses the full proton-proton data set recorded by ATLAS in 2011 and. The data considered here were selected using a diphoton trigger in which two clusters formed from energy depositions in the electromagnetic calorimeter are required.
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