Browsing by Author "Do Valle Wemans, Andre"
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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 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.
- Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at $\sqrt{s}=7$ TeV with the ATLAS detectorPublication . ATLAS collaboration (3020 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, HelmutThis letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of pT in the range 4 < pT < 100 GeV and within pseudorapidity |eta| < 2.5. In addition the electron and muon cross-sections are measured in the range 7 < pT < 26 GeV and within |eta| <2.0, excluding 1.37<|eta|<1.52. Integrated luminosities of 1.3 pb-1 and 1.4 pb-1 are used for the electron and muon measurements, respectively. After subtraction of the W/Z/gamma* contribution, the differential cross-sections are found to be in good agreement with theoretical predictions for heavy-flavour production obtained from Fixed Order NLO calculations with NLL high-pT resummation, and to be sensitive to the effects of NLL resummation.
- Performance of Missing Transverse Momentum Reconstruction in Proton-Proton Collisions at 7 TeV with ATLASPublication . ATLAS collaboration (3031 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, HelmutThe measurement of missing transverse momentum in the ATLAS detector, described in this paper, makes use of the full event reconstruction and a calibration based on reconstructed physics objects. The performance of the missing transverse momentum reconstruction is evaluated using data collected in pp collisions at a centre-of-mass energy of 7 TeV in 2010. Minimum bias events and events with jets of hadrons are used from data samples corresponding to an integrated luminosity of about 0.3 inverse nb and 600 inverse nb, together with events containing a Z boson decaying to two leptons (electrons or muons) or a W boson decaying to a lepton (electron or muon) and a neutrino, from a data sample corresponding to an integrated luminosity of about 36 inverse pb. An estimate of the systematic uncertainty on the missing transverse momentum scale is presented.