A measurement of the Lambda_b lifetime and mass in the decay channel Lambda_b -> J/psi(mu^+ mu^-) Lambda^0(p pi^-) is presented. The analysis uses a signal sample of about 2200 Lambda_b and ...anti-Lambda_b decays that are reconstructed in 4.9 fb^-1 of ATLAS pp collision data collected in 2011 at the LHC center-of-mass energy of 7 TeV. A simultaneous mass and decay time maximum likelihood fit is used to extract the Lambda_b lifetime and mass. They are measured to be tau(Lambda_b) = 1.449 ± 0.036(stat) ± 0.017(syst) ps andm(Lambda_b) = 5619.7 ± 0.7(stat) ± 1.1(syst) MeV.
This paper presents a measurement of the W^+W^- production cross section in pp collisions at sqrt{s}=7 TeV. The leptonic decay channels are analyzed using data corresponding to an integrated 4.6 fb-1 ...collected with the ATLAS detector at the Large Hadron Collider. The W^+W^- production cross section sigma(pp -> W^+W^-+X) is measured to be 51.9 +- 2.0 (stat) +- 3.9 (syst) +- 2.0 (lumi) pb, compatible with the Standard Model prediction of 44.7 +2.1 -1.9 pb. A measurement of the normalized fiducial cross section as a function of the leading lepton transverse momentum is also presented. The reconstructed transverse momentum distribution of the leading lepton is used to extract limits on anomalous WWZ and WWgamma couplings.
A generic search is presented for a heavy particle decaying to WZ to l nu l'l' (l, l' = e, mu) final states. The data were recorded by the ATLAS detector in sqrt(s) = 7 TeV pp collisions at the Large ...Hadron Collider and correspond to an integrated luminosity of 1.02 fb-1. The transverse mass distribution of the selected WZ candidates is found to be consistent with the Standard Model expectation. Upper limits on the production cross section times branching ratio are derived using two benchmark models predicting a heavy particle decaying to a WZ pair.
We present an update of a search for supersymmetry in final states containing jets, missing transverse momentum, and one isolated electron or muon, using 1.04 fb^-1 of proton-proton collision data at ...sqrt{s} = 7 TeV recorded by the ATLAS experiment at the LHC in the first half of 2011. The analysis is carried out in four distinct signal regions with either three or four jets and variations on the (missing) transverse momentum cuts, resulting in optimized limits for various supersymmetry models. No excess above the standard model background expectation is observed. Limits are set on the visible cross-section of new physics within the kinematic requirements of the search. The results are interpreted as limits on the parameters of the minimal supergravity framework, limits on cross-sections of simplified models with specific squark and gluino decay modes, and limits on parameters of a model with bilinear R-parity violation.
This paper presents a search for a new heavy particle produced in association with a top or antitop quark. Two models in which the new heavy particle is a color singlet or a color triplet are ...considered, decaying respectively to tbarq or tq, leading to a resonance within the ttbar + jets signature. The full 2011 ATLAS pp collision dataset from the LHC (4.7 fb-1) is used to search for ttbar events produced in association with jets, in which one of the W bosons from the top quarks decays leptonically and the other decays hadronically. The data are consistent with the Standard Model expectation, and a new particle with mass below 430 GeV for both W boson and color triplet models is excluded at 95% confidence level, assuming unit right-handed coupling.
The production of Kshort and Lambda hadrons is studied in inelastic pp collisions at sqrt(s) = 0.9 and 7 TeV collected with the ATLAS detector at the LHC using a minimum-bias trigger. The observed ...distributions of transverse momentum, rapidity, and multiplicity are corrected to hadron level in a model-independent way within well defined phase-space regions. The distribution of the production ratio of Lambdabar to Lambda baryons is also measured. The results are compared with various Monte Carlo simulation models. Although most of these models agree with data to within 15% in the Kshort distributions, substantial disagreements with data are found in the Lambda distributions of transverse momentum.
Afin d'évaluer l'intérêt d'un nouveau substrat pour la détection des anticorps anti-nucléaires (AAN) par immunofluorescence indirecte, les cellules HEp-2000
®, une étude multicentrique impliquant 19 ...laboratoires et 1 253 sérums a été réalisée. Chaque laboratoire a analysé environ 40 sérums témoins de sa propre sérothèque (10 négatifs et 30 positifs correspondant aux principaux types de fluorescence) et 30 sérums « tout-venant å. Chaque sérum a été testé en parallèle, à la dilution de
1
80
, sur HEp-2000
® et sur le substrat habituel du laboratoire. Pour les différents types de fluorescence, la concordance des résultats obtenus sur les deux substrats était globalement de 93 % (de 83 à 100 % selon le laboratoire). Pour 17 sérums, les cellules HEp-2000
® ont permis de mettre en évidence des anticorps anti-SSA qui n'avaient pas été décelés sur le substrat de routine ; à l'inverse, un seul sérum a paru négatif sur HEp-2000
® alors que des anticorps anti-SSA ont été mis en évidence sur le substrat habituel du laboratoire. En conclusion, les cellules HEp-2000
® permettent de détecter les anticorps anti-SSA avec une plus forte sensibilité que les substrats classiques, tout en fournissant pour les autres AAN des résultats très similaires.
To evaluate the performances of HEp-2000
® cells as a new substrate for the detection of anti-nuclear antibodies (ANA) by indirect immunofluorescence, a multicentric study was performed, involving 19 laboratories and 1253 sera. Each laboratory tested about 70 sera: 40 control sera from its own collection (10 negative and 30 positive with the most common fluorescence aspects), and 30 unsorted sera from their daily practice. All sera were tested at the
1
80
dilution on HEp-2000
® and on the substrate routinely used in the laboratory. There was a 93% agreement (from 83 to 100% according to the laboratory) between the fluorescence aspects observed on both substrates. For anti-SSA antibodies, 17 samples were positive with HEp-2000
® and negative with the routine substrate, whereas only one serum was negative on HEp-2000
® and positive with the routine substrate. We conclude that HEp-2000
® cells are more sensitive than the usual substrates for the detection of anti-SSA antibodies, while producing similar results for the other ANA.
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