Browsing by Author "ATLAS collaboration (2834 authors)"
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- Determination of the top-quark pole mass using $ t\overline{t} $ + 1-jet events collected with the ATLAS experiment in 7 TeV pp collisionsPublication . ATLAS collaboration (2834 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; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutThe normalized differential cross section for top-quark pair production in association with at least one jet is studied as a function of the inverse of the invariant mass of the $ t\overline{t} $ + 1-jet system. This distribution can be used for a precise determination of the top-quark mass since gluon radiation depends on the mass of the quarks. The experimental analysis is based on proton-proton collision data collected by the ATLAS detector at the LHC with a centre-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.6 fb$^{−1}$. The selected events were identified using the lepton+jets top-quark-pair decay channel, where lepton refers to either an electron or a muon. The observed distribution is compared to a theoretical prediction at next-to-leading-order accuracy in quantum chromodynamics using the pole-mass scheme. With this method, the measured value of the top-quark pole mass, m$_{t}^{pole}$ , is: $ {m}_t^{\mathrm{pole}}=173.7\pm 1.5\left(\mathrm{stat}.\right)\pm 1.4{\left(\mathrm{syst}.\right)}_{-0.5}^{+1.0}\left(\mathrm{theory}\right)\mathrm{GeV}. $
- Measurements of top-quark pair to $Z$-boson cross-section ratios at $\sqrt s = 13, 8, 7$ TeV with the ATLAS detectorPublication . ATLAS collaboration (2834 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; 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; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Oleiro Seabra, Luis Filipe; Onofre, António; Pedro, Rute; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutRatios of top-quark pair to Z-boson cross sections measured from proton-proton collisions at the LHC centre-of-mass energies of $ \sqrt{s}=13 $ TeV, 8 TeV, and 7 TeV are presented by the ATLAS Collaboration. Single ratios, at a given $ \sqrt{s} $ for the two processes and at different $ \sqrt{s} $ for each process, as well as double ratios of the two processes at different $ \sqrt{s} $ , are evaluated. The ratios are constructed using previously published ATLAS measurements of the $ t\overline{t} $ and Z-boson production cross sections, corrected to a common phase space where required, and a new analysis of Z → ℓ$^{+}$ℓ$^{−}$ where ℓ = e, μ at $ \sqrt{s}=13 $ TeV performed with data collected in 2015 with an integrated luminosity of 3.2 fb$^{−1}$. Correlations of systematic uncertainties are taken into account when evaluating the uncertainties in the ratios. The correlation model is also used to evaluate the combined cross section of the Z → e$^{+}$ e$^{−}$ and the Z → μ$^{+}$ μ$^{−}$ channels for each $ \sqrt{s} $ value. The results are compared to calculations performed at next-to-next-to-leading-order accuracy using recent sets of parton distribution functions. The data demonstrate significant power to constrain the gluon distribution function for the Bjorken-x values near 0.1 and the light-quark sea for x < 0.02.