Search for single top-quark production via FCNC at 8TeV with ATLAS

Abstract

A search for single top-quark production via flavour changing neutral current processes from gluon plus upor charm–quark initial states in proton–proton collisions at the LHC is presented. Data collected with the ATLAS detector in 2012 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 signaland backgroundlike candidates using a neural network. No signal is observed and an upper limit on the production cross-section multiplied by the t →Wb branching fraction is set. The observed 95% CL limit is σqg→t×B(t→Wb)< 3.4 pb and the expected 95% CL limit is σqg→t×B(t→Wb)< 2.9 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 κugt/Λ < 5.8× 10−3 TeV−1 and κcgt/Λ < 13× 10−3 TeV−1 and on the branching fractions B(t → ug) < 4× 10−5 and B(t→ cg)< 17×10−5.