Browsing by Author "ATLAS collaboration (3024 authors)"
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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 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.
- Search for New Physics in the Dijet Mass Distribution using 1 fb$^{-1}$ of $pp$ Collision Data at $\sqrt{s}=$7 TeV collected by 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, HelmutInvariant mass distributions of jet pairs (dijets) produced in LHC proton-proton collisions at a centre-of-mass energy sqrt(s)=7 TeV have been studied using a data set corresponding to an integrated luminosity of 1.0 fb^-1 recorded in 2011 by ATLAS. Dijet masses up to ~4 TeV are observed in the data, and no evidence of resonance production over background is found. Limits are set at 95% CL for several new physics hypotheses: excited quarks are excluded for masses below 2.99 TeV, axigluons are excluded for masses below 3.32 TeV, and colour octet scalar resonances are excluded for masses below 1.92 TeV.
- Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in $\sqrt{s}=7$ TeV proton-proton collisionsPublication . 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 search for squarks and gluinos in events containing jets, missing transverse momentum and no electrons or muons is presented. The data were recorded in 2011 by the ATLAS experiment in sqrt(s) = 7 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation is observed in 1.04 fb^-1 of data. Gluino and squark masses below 700 GeV and 875 GeV respectively are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino. The exclusion limit increases to 1075 GeV for squarks and gluinos of equal mass. In MSUGRA/CMSSM models with tan(beta)=10, A_0=0 and mu> 0, squarks and gluinos of equal mass are excluded for masses below 950 GeV. These limits extend the region of supersymmetric parameter space excluded by previous measurements.