Repository logo

Browsing by Issue Date, starting with "2016-01-08"

Filter results by year or month
Now showing 1 - 2 of 2
  • Search for flavour-changing neutral current top-quark decays to $qZ$ in $pp$ collision data collected with the ATLAS detector at $\sqrt s =8$  TeV
    Publication . ATLAS collaboration (2855 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Onofre, António; Palma, Alberto; Pedro, Rute; Pina, João Antonio; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, Helmut
    A search for the flavour-changing neutral-current decay $t\rightarrow qZ$ 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 $\sqrt{s}=8$  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 $t\rightarrow qZ$ ( $q=u,c$ ) channel and the other through the dominant Standard Model mode $t\rightarrow bW$ 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 $t\rightarrow qZ$ branching ratio of $7\times 10^{-4}$ ( $8\times 10^{-4}$ ) is set at the 95 % confidence level
    2016-01-08Journal article Open access Show more
  • Search for resonant $t \bar t$ production in proton-proton collisions at $\sqrt s=$ 8  TeV
    Publication . CMS collaboration (2308 authors); Hollar, Jonathan; Calpas, Betty; Nayak, Aruna; Bargassa, Pedrame; Beirão Da Cruz E Silva, Cristóvão; Di Francesco, Agostino; Faccioli, Pietro; Ferreira Parracho, Pedro Guilherme; Gallinaro, Michele; Lloret Iglesias, Lara; Nguyen, Federico; Rodrigues Antunes, Joao; Seixas, Joao; Toldaiev, Oleksii; Vadruccio, Daniele; Varela, Joao; Vischia, Pietro; David Tinoco Mendes, Andre; Silva, Pedro; Musella, Pasquale; Pela, Joao; Leonardo, Nuno
    A search is performed for the production of heavy resonances decaying into top-antitop quark pairs in proton-proton collisions at s=8  TeV. Data used for the analyses were collected with the CMS detector and correspond to an integrated luminosity of 19.7  fb−1. The search is performed using events with three different final states, defined by the number of leptons (electrons and muons) from the tt¯→WbWb decay. The analyses are optimized for reconstruction of top quarks with high Lorentz boosts, where jet substructure techniques are used to enhance the sensitivity. Results are presented for all channels and a combination is performed. No significant excess of events relative to the expected yield from standard model processes is observed. Upper limits on the production cross section of heavy resonances decaying to tt¯ are calculated. A narrow leptophobic topcolor Z′ resonance with a mass below 2.4 TeV is excluded at 95% confidence level. Limits are also derived for a broad Z′ resonance with a 10% width relative to the resonance mass, and a Kaluza-Klein excitation of the gluon in the Randall-Sundrum model. These are the most stringent limits to date on heavy resonances decaying into top-antitop quark pairs.
    2016-01-08Journal article Open access Show more