Browsing by Author "Carvalho, Joao"
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- A measurement of the ratio of the $W$ and $Z$ cross sections with exactly one associated jet in $pp$ collisions at $\sqrt{s}=$7 TeV with ATLASPublication . ATLAS collaboration (3024 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, Joao; Castro, Nuno Filipe; Conde Muino, Patricia; Do Valle Wemans, Andre; Fiolhais, Miguel; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Oliveira, Miguel Alfonso; Onofre, Antonio; Palma, Alberto; Pina, Joao Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, Joao; Silva, Jose; Soares, Mara; Veloso, Filipe; Wolters, HelmutThe ratio of production cross sections of the W and Z bosons with exactly one associated jet is presented as a function of jet transverse momentum threshold. The measurement has been designed to maximise cancellation of experimental and theoretical uncertainties, and is reported both within a particle-level kinematic range corresponding to the detector acceptance and as a total cross-section ratio. Results are obtained with the ATLAS detector at the LHC in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 33 pb^-1. The results are compared with perturbative leading-order, leading-log, and next-to-leading-order QCD predictions, and are found to agree within experimental and theoretical uncertainties. The ratio is measured for events with a single jet with p_T > 30 GeV to be 8.73 +/- 0.30 (stat) +/- 0.40 (syst) in the electron channel, and $ 8.49 +/- 0.23 (stat) +/- 0.33 (syst) in the muon channel.
- Measurement of $\chi_{c1}$ and $\chi_{c2}$ production with $\sqrt{s}$ = 7 TeV $pp$ collisions at ATLASPublication . ATLAS collaboration (2932 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Cantrill, Robert; Carvalho, Joao; Castro, Nuno Filipe; Conde Muino, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Do Valle Wemans, Andr\'e; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gon\c calo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Am\'elia; Maneira, Jos\'e; Marques, Carlos; Oliveira, Miguel Alfonso; Onofre, Ant\'onio; Palma, Alberto; Pedro, Rute; Pina, Joao Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, Joao; Silva, Jos\'e; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutThe prompt and non-prompt production cross-sections for the chi_c1 and chi_c2 charmonium states are measured in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector at the LHC using 4.5 fb^-1 of integrated luminosity. The chi_c states are reconstructed through the radiative decay chi_c -> J/psi gamma (with J/psi -> mu+mu-) where photons are reconstructed from gamma -> e+e- conversions. The production rate of the chi_c2 state relative to the chi_c1 state is measured for prompt and non-prompt chi_c as a function of J/psi transverse momentum. The prompt chi_c cross-sections are combined with existing measurements of prompt J/psi production to derive the fraction of prompt J/psi produced in feed-down from chi_c decays. The fractions of chi_c1 and chi_c2 produced in b-hadron decays are also measured.
- Measurement of jet fragmentation in 5.02 TeV proton-lead and proton-proton collisions with the ATLAS detectorPublication . ATLAS collaboration (2849 authors); Aguilar Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque Espinosa, Juan Pedro; Carvalho, Joao; Castro, Nuno Filipe; Conde Muino, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Oleiro Seabra, Luis Filipe; Onofre, Antonio; Costa Batalha Pedro, Rute; Santos, Helena; Saraiva, Joao; Silva, Jose Manuel; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutA measurement of the fragmentation functions of jets into charged particles in $p$+Pb collisions and $pp$ collisions is presented. The analysis utilizes 28 nb$^{-1}$ of $p$+Pb data and 26 pb$^{-1}$ of $pp$ data, both at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV, collected in 2013 and 2015, respectively, with the ATLAS detector at the LHC. The measurement is reported in the centre-of-mass frame of the nucleon-nucleon system for jets in the rapidity range $|y^{*}|
- Measurement of the $W \to \tau \nu_\tau$ cross section in $pp$ collisions at $\sqrt{s}=$7 TeV with the ATLAS experimentPublication . ATLAS collaboration (3024 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, Joao; Castro, Nuno Filipe; Conde Muino, Patricia; Do Valle Wemans, Andre; Fiolhais, Miguel; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Oliveira, Miguel Alfonso; Onofre, Antonio; Palma, Alberto; Pina, Joao Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, Joao; Silva, Jose; Soares, Mara; Veloso, Filipe; Wolters, HelmutThe cross section for the production of W bosons with subsequent decay W to tau nu is measured with the ATLAS detector at the LHC. The analysis is based on a data sample that was recorded in 2010 at a proton-proton center-of-mass energy of sqrt(s) = 7 TeV and corresponds to an integrated luminosity of 34 pb^-1. The cross section is measured in a region of high detector acceptance and then extrapolated to the full phase space. The product of the total W production cross section and the W to tau nu branching ratio is measured to be 11.1 +/- 0.3 (stat) +/- 1.7 (syst) +/- 0.4 (lumi) nb.
- Measurement of the cross section for the production of a $W$ boson in association with $b^-$ jets in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detectorPublication . ATLAS collaboration (3024 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, Joao; Castro, Nuno Filipe; Conde Muino, Patricia; Do Valle Wemans, Andre; Fiolhais, Miguel; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Oliveira, Miguel Alfonso; Onofre, Antonio; Palma, Alberto; Pina, Joao Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, Joao; Silva, Jose; Soares, Mara; Veloso, Filipe; Wolters, HelmutA measurement is presented of the cross section for the production of a W boson with one or two jets, of which at least one must be a b-jet, in pp collisions at sqrt(s)=7 TeV. Production via top decay is not included in the signal definition. The measurement is based on 35 pb^-1 of data collected with the ATLAS detector at the LHC. The W+b-jet cross section is defined for jets reconstructed with the anti-kt clustering algorithm with transverse momentum above 25 GeV and rapidity within +/-2.1. The b-jets are identified by reconstructing secondary vertices. The fiducial cross section is measured both for the electron and muon decay channel of the W boson and is found to be 10.2 +/- 1.9 (stat) +/- 2.6 (syst) pb for one lepton flavour. The results are compared with next-to-leading order QCD calculations, which predict a cross section smaller than, though consistent with, the measured value.
- Measurement of the cross-section for $b$-jets produced in association with a $Z$ boson at $\sqrt{s}=$ 7 TeV with the ATLAS detectorPublication . ATLAS collaboration (3026 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, Joao; Castro, Nuno Filipe; Conde Muino, Patricia; Do Valle Wemans, Andre; Fiolhais, Miguel; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Oliveira, Miguel Alfonso; Onofre, Antonio; Palma, Alberto; Pina, Joao Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, Joao; Silva, Jose; Soares, Mara; Veloso, Filipe; Wolters, HelmutA measurement is presented of the cross-section for b-jet production in association with a Z boson in pp collisions at a centre-of-mass energy of sqrt(s)=7 TeV. The analysis uses the data sample collected by the ATLAS experiment in 2010, corresponding to an integrated luminosity of approximately 36 pb^-1. The event selection requires a Z boson decaying into high pt electrons or muons, and a b-jet, identified by its displaced vertex, with transverse momentum pt>25 GeV and rapidity |y|<2.1. After subtraction of backgrounds, the yield is extracted from the vertex mass distribution of the candidate b-jets. The ratio of this cross-section to the inclusive Z cross-section (the average number of b-jets per Z event) is also measured. Both results are found to be in good agreement with perturbative QCD predictions at next-to-leading order.
- Measurement of the inclusive $W^\pm$ and Z/gamma cross sections in the electron and muon decay channels in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detectorPublication . ATLAS collaboration (3026 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, Joao; Castro, Nuno Filipe; Conde Muino, Patricia; Do Valle Wemans, Andre; Fiolhais, Miguel; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Oliveira, Miguel Alfonso; Onofre, Antonio; Palma, Alberto; Pina, Joao Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, Joao; Silva, Jose; Soares, Mara; Veloso, Filipe; Wolters, HelmutThe production cross sections of the inclusive Drell-Yan processes W to l nu and Z/gamma to ll (l=e,mu) are measured in proton-proton collisions at sqrt(s) = 7 TeV with the ATLAS detector. The cross sections are reported integrated over a fiducial kinematic range, extrapolated to the full range and also evaluated differentially as a function of the W decay lepton pseudorapidity and the Z boson rapidity, respectively. Based on an integrated luminosity of about 35 pb^-1 collected in 2010, the precision of these measurements reaches a few per cent. The integrated and the differential W+- and Z/gamma cross sections in the e and mu channels are combined, and compared with perturbative QCD calculations, based on a number of different parton distribution sets available at NNLO.
- Measurement of the isolated di-photon cross-section in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detectorPublication . ATLAS collaboration (3034 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, Joao; Castro, Nuno Filipe; Conde Muino, Patricia; Do Valle Wemans, Andre; Fiolhais, Miguel; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Magalhaes Martins, Paulo Jorge; Maio, Amelia; Maneira, Jose; Morais, Antonio; Oliveira, Miguel Alfonso; Onofre, Antonio; Palma, Alberto; Pina, Joao Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, Joao; Silva, Jose; Soares, Mara; Veloso, Filipe; Wolters, HelmutThe ATLAS experiment has measured the production cross-section of events with two isolated photons in the final state, in proton-proton collisions at sqrt(s) = 7 TeV. The full data set acquired in 2010 is used, corresponding to an integrated luminosity of 37 pb^-1. The background, consisting of hadronic jets and isolated electrons, is estimated with fully data-driven techniques and subtracted. The differential cross-sections, as functions of the di-photon mass, total transverse momentum and azimuthal separation, are presented and compared to the predictions of next-to-leading-order QCD.
- Measurement of the top quark pair production cross section in $pp$ collisions at $\sqrt{s}=7$ TeV in dilepton final states with ATLASPublication . ATLAS collaboration (3035 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, Joao; Castro, Nuno Filipe; Conde Muino, Patricia; Do Valle Wemans, Andre; Fiolhais, Miguel; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Magalhaes Martins, Paulo Jorge; Maio, Amelia; Maneira, Jose; Oliveira, Miguel Alfonso; Onofre, Antonio; Palma, Alberto; Pina, Joao Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, Joao; Silva, Jose; Soares, Mara; Veloso, Filipe; Wolters, HelmutA measurement of the production cross section of top quark pairs (ttbar) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of 35 pb^-1, a ttbar production cross section of 171 +/- 20(stat.) +/- 14(syst.) +8-6(lum.) pb is measured for an assumed top quark mass of 172.5 GeV. A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states are consistent with being accompanied by b-quark jets. These measurements are in good agreement with Standard Model predictions.
- Measurement of the Transverse Momentum Distribution of $W$ Bosons in $pp$ Collisions at $\sqrt{s}=7$ TeV with the ATLAS DetectorPublication . ATLAS collaboration (3024 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, Joao; Castro, Nuno Filipe; Conde Muino, Patricia; Do Valle Wemans, Andre; Fiolhais, Miguel; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Oliveira, Miguel Alfonso; Onofre, Antonio; Palma, Alberto; Pina, Joao Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, Joao; Silva, Jose; Soares, Mara; Veloso, Filipe; Wolters, HelmutThis paper describes a measurement of the W boson transverse momentum distribution using ATLAS pp collision data from the 2010 run of the LHC at sqrt(s) = 7 TeV, corresponding to an integrated luminosity of about 31 pb^-1. Events from both W -> e nu and W -> mu nu are used, and the transverse momentum of the W candidates is measured through the energy deposition in the calorimeter from the recoil of the W. The resulting distributions are unfolded to obtain the normalized differential cross sections as a function of the W boson transverse momentum. We present results for pTW < 300 GeV in the electron and muon channels as well as for their combination, and compare the combined results to the predictions of perturbative QCD and a selection of event generators.