Search for single top-quark production via flavour-changing neutral currents at 8 TeV with the ATLAS detector

This poster presents a search for single top-quark production via flavour-changing neutral current processes from gluon plus up- or charm-quark initial states in proton-proton collisions at the LHC. Data collected with the ATLAS detector at a centre-of-mass energy of 8 TeV and corresponding to an integrated luminosity of 20.3 fb$^{-1}$ are used. Candidate events for a top quark decaying into a lepton, a neutrino and a jet are selected and classified into signal- and background-like candidates using a neural network. No signal is observed and an upper limit on the production cross-section multiplied by the $t \rightarrow Wb$ branching fraction is set. The observed 95 \% C.L. limit is $\sigma_{qg \rightarrow t} \times B(t \rightarrow Wb)< 3.4$ pb The observed limit can be interpreted as upper limits on the coupling constants of the flavour-changing neutral current interactions divided by the scale of new physics $\kappa_{ugt}/\Lambda < 5.8\cdot 10^{-3}$ TeV$^{-1}$ and $\kappa_{cgt}/\Lambda < 13\cdot 10^{-3}$ TeV$^{-1}$ and on the branching fractions $B(t \rightarrow ug) < 4.0\cdot 10^{-5}$ and $B(t \rightarrow cg) < 17 \cdot 10^{-5}$.