A search for flavor-changing neutral currents in top-quark decays t→Zq is performed in events produced from the decay chain tt¯→Zq+Wb, where both vector bosons decay leptonically, producing a final state with three leptons (electrons or muons). A data set collected with the CMS detector at the LHC is used, corresponding to an integrated luminosity of 19.7  fb−1 of proton-proton collisions at a center-of-mass energy of 8 TeV. No excess is seen in the observed number of events relative to the standard model prediction; thus, no evidence for flavor-changing neutral currents in top-quark decays is found. A combination with a previous search at 7 TeV excludes a t→Zq branching fraction greater than 0.05% at the 95% confidence level.



Titolo: Search for flavor-changing neutral currents in top-quark decays t -> Zq in pp collisions at sqrt(s) = 8 TeV
Autori: 
CANDELISE, VIERI
DELLA RICCA, GIUSEPPE
LA LICATA, CHIARA
MARONE, MATTEO
MONTANINO, DAMIANA
SCHIZZI, ANDREA
UMER, TOMO
mostra contributor esterni 
Data di pubblicazione: 2014
Rivista: 
PHYSICAL REVIEW LETTERS  
Abstract: A search for flavor-changing neutral currents in top-quark decays t→Zq is performed in events produced from the decay chain tt¯→Zq+Wb, where both vector bosons decay leptonically, producing a final state with three leptons (electrons or muons). A data set collected with the CMS detector at the LHC is used, corresponding to an integrated luminosity of 19.7  fb−1 of proton-proton collisions at a center-of-mass energy of 8 TeV. No excess is seen in the observed number of events relative to the standard model prediction; thus, no evidence for flavor-changing neutral currents in top-quark decays is found. A combination with a previous search at 7 TeV excludes a t→Zq branching fraction greater than 0.05% at the 95% confidence level.
Handle: http://hdl.handle.net/11368/2736693
Digital Object Identifier (DOI): 10.1103/PhysRevLett.112.171802
URL: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.171802
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