Search for flavour-changing neutral current top-quark decays to q Z in pp collision data collected with the ATLAS detector at root s=8 TeV

Aad, G. ; Abbott, B. ; Abdallah, J. ; Abdinov, O. ; Aben, R. ; Abolins, M. ; AbouZeid, O. S. ; Abramowicz, H. ; Abreu, H. and Abreu, R. , et al. (2016) In European Physical Journal C. Particles and Fields 76(1).
A search for the flavour-changing neutral-current decay is presented. Data collected by the ATLAS detector during 2012 from proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of root s = 8 TeV, corresponding to an integrated luminosity of 20.3 fb(-1), are analysed. Top-quark pair-production events with one top quark decaying through the t -> qZ (q = u,c) channel and the other through the dominant Standard Model mode t -> bW are considered as signal. Only the decays of the Z boson to charged leptons and leptonic W boson decays are used. No evidence for a signal is found and an observed (expected) upper limit on the t -> qZ branching ratio of 7 x 10(-4) (8 x 10(-4)) is set at the 95 % confidence level.
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