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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 detector  [PDF]
ATLAS Collaboration
Statistics , 2011, DOI: 10.1016/j.physletb.2011.12.046
Abstract: A 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 W boson production in association with b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector  [PDF]
The ATLAS Collaboration
Statistics , 2013, DOI: 10.1007/JHEP06(2013)084
Abstract: This paper reports a measurement of the W+b-jets production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6 fb-1, collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the muon and electron decay modes of the W boson. The W+b-jets cross-section, corrected for all known detector effects, is quoted in a limited kinematic range, using jets reconstructed with the anti-k_t clustering algorithm with transverse momentum above 25 GeV and rapidity within +/- 2.1. Combining the muon and electron channels, the fiducial cross-section for W+b-jets is measured to be 7.1 +/- 0.5 (stat) +/- 1.4 (syst) pb, consistent with next-to-leading order QCD calculations within 1.5 standard deviations.
Study of Vector Boson Fusion Higgs in Atlas-LHC  [PDF]
Dimitris Varouchas
Physics , 2008,
Abstract: Within the framework of Standard Model, the production mode of Higgs boson through the fusion of the vector bosons $W$ or $Z$ (Vector Boson Fusion) is one of the most important production mechanisms, providing a specific detection signature. A detailed study regarding this issue is being undergone for ATLAS detector in LHC and some general features of this analysis are being presented in this note emphasizing in the study of Central Jet Veto.
Jet vetoes versus giant K-factors in the exclusive Z+1-jet cross section  [PDF]
Radja Boughezal,Christfried Focke,Xiaohui Liu
Physics , 2015, DOI: 10.1103/PhysRevD.92.094002
Abstract: We perform a detailed study of the exclusive Z+1-jet cross section at the 13 TeV LHC, motivated by the importance of similar exclusive cross sections in understanding the production of the Higgs boson in the W^+W^- final state. We point out a feature of the ATLAS analysis that has significant impact on the theoretical predictions: the jet-isolation criterion implemented by ATLAS effectively allows dijet events where an energetic jet is collinear to a final-state lepton. This process contains a giant $K$-factor arising from the collinear emission of a Z-boson from the dijet configuration. This overwhelms the effect of the jet-veto logarithms, making it difficult to test their resummation in this process. We provide numerical results that demonstrate the interplay between the jet-veto logarithms and the giant K-factor in the theoretical prediction. We study several observables, including the transverse momentum distributions of the leading jet and the Z-boson, in the exclusive Z+1-jet process, and discuss their sensitivity to both the giant K-factor and the jet-veto logarithms. We suggest a modified isolation criterion that removes the giant K-factor and allows for a direct test of the jet-veto resummation framework in the exclusive Z+1-jet process.
Discovery Potential of the Standard Model Higgs Boson Through H -> WW Decay Mode with the ATLAS Detector at LHC  [PDF]
Hai-Jun Yang,for the ATLAS Collaboration
Physics , 2009,
Abstract: We report results of a study of the Standard Model Higgs boson discovery potential through the W-pair leptonic decay modes with the ATLAS detector at LHC at 14 TeV center-of-mass energy. We used MC samples with full detector simulation and reconstruction of the ATLAS experiment to estimate the ATLAS detection sensitivity for the reaction of pp -> H -> WW -> e\nu \mu\nu with no hard jet or two hard jets in the final states. The prospects for the Higgs boson searches at ATLAS are presented, including trigger efficiencies and data-driven methods to estimate the backgrounds using control samples in data. With 10/fb of integrated luminosity, one would expect to discover a Standard Model Higgs boson with ATLAS detector in Higgs boson mass range 135 < m_H < 190 GeV. If the Higgs boson does not exist, we will extend and confirm the exclusion produced by the Tevatron Higgs boson search result, which has ruled out the Higgs boson mass range of 160 < m_H < 170 GeV at 95% confidence level. If Higgs boson would be discovered, ATLAS could measure its mass with a precision of about 2 and 7 GeV for Higgs boson mass around 160 GeV and 130 GeV, respectively.
Jet quenching measurements with ATLAS at LHC  [PDF]
W. K. Brooks
Physics , 2010, DOI: 10.1063/1.3480184
Abstract: A broad program of measurements is planned for heavy ion collisions in ATLAS. With up to a factor of 30 increase in collision energy compared to existing data, significant new insights are anticipated to be obtained with the first data measured. Global features of the LHC collisions will be accessible with the early data and will set the stage for the precision measurements to follow. ATLAS is particularly well suited for exploration of "jet quenching," the extinction of energetic jets in the hot dense medium. Observations of heavy quark jet suppression will be possible with unprecedented energy reach and statistical precision, potentially yielding new insights into the basic mechanisms involved.
Measurement of the production cross section for W-bosons in association with jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector  [PDF]
The ATLAS Collaboration
Physics , 2010, DOI: 10.1016/j.physletb.2011.03.012
Abstract: This Letter reports on a first measurement of the inclusive W+jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the W boson, are presented as a function of jet multiplicity and of the transverse momentum of the leading and next-to-leading jets in the event. Measurements are also presented of the ratio of cross sections sigma(W+ \ge n) / sigma(W+ \ge n-1) for inclusive jet multiplicities n=1-4. The results, based on an integrated luminosity of 1.3 pb-1, have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The measured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations, studied here for n \le 2, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicities.
SUSY QCD corrections to electroweak gauge boson production with an associated jet at the LHC  [PDF]
Ryan Gavin,Maike K. Trenkel
Physics , 2011, DOI: 10.1007/JHEP01(2012)036
Abstract: We study the stability of the neutral- and charged-current Drell-Yan process in association with a jet as a standard candle at the LHC under the inclusion of O(alpha_s) supersymmetric QCD (SQCD) corrections within the MSSM. We include the decay of the electroweak gauge boson into dileptons, i.e. we consider the production of charged lepton--anti-lepton or lepton-neutrino final states with one hard jet. We find that the SQCD corrections are negligible for the integrated cross section. Only at high lepton transverse momentum can they induce effects of the percent level.
Study of jets produced in association with a W boson in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector  [PDF]
ATLAS Collaboration
Physics , 2012, DOI: 10.1103/PhysRevD.85.092002
Abstract: We report a study of final states containing a W boson and hadronic jets, produced in proton-proton collisions at a center-of-mass energy of 7 TeV. The data were collected with the ATLAS detector at the CERN LHC and comprise the full 2010 data sample of 36 pb^-1. Cross sections are determined using both the electron and muon decay modes of the W boson and are presented as a function of inclusive jet multiplicity, N_jet, for up to five jets. At each multiplicity, cross sections are presented as a function of jet transverse momentum, the scalar sum of the transverse momenta of the charged lepton, missing transverse momentum, and all jets, the invariant mass spectra of jets, and the rapidity distributions of various combinations of leptons and final-state jets. The results, corrected for all detector effects and for all backgrounds such as diboson and top quark pair production, are compared with particle-level predictions from perturbative QCD. Leading-order multiparton event generators, normalized to the NNLO total cross section for inclusive W-boson production, describe the data reasonably well for all measured inclusive jet multiplicities. Next-to-leading-order calculations from MCFM, studied here for N_jet >= 2, and BlackHat-Sherpa, studied here for N_jet >= 4, are found to be mostly in good agreement with the data.
Observation and measurement of Higgs boson decays to $WW^{\ast}$ with the ATLAS detector  [PDF]
ATLAS Collaboration
Statistics , 2014, DOI: 10.1103/PhysRevD.92.012006
Abstract: We report the observation of Higgs boson decays to $WW^{\ast}$ based on an excess over background of $6.1$ standard deviations in the dilepton final state, where the Standard Model expectation is $5.8$ standard deviations. Evidence for the vector-boson fusion (VBF) production process is obtained with a significance of 3.2 standard deviations. The results are obtained from a data sample corresponding to an integrated luminosity of $25\,\textrm{fb}^{-1}$ from $\sqrt{s}=7$ and 8 TeV $pp$ collisions recorded by the ATLAS detector at the LHC. For a Higgs boson mass of 125.36 GeV, the ratio of the measured value to the expected value of the total production cross section times branching fraction is $1.09^{+0.16}_{-0.15}\,\textrm{(stat)}^{+0.17}_{-0.14}\,\textrm{(syst)}$. The corresponding ratios for the gluon fusion and vector-boson fusion production mechanisms are $1.02\pm 0.19\,\textrm{(stat)}^{+0.22}_{-0.18}\,\textrm{(syst)}$ and $1.27^{+0.44}_{-0.40}\,\textrm{(stat)}^{+0.30}_{-0.21}\,\textrm{(syst)}$, respectively. At $\sqrt{s}=8$ TeV, the total production cross sections are measured to be $\sigma(gg\to$ $H\rightarrow WW^\ast) = 4.6\pm0.9\,\textrm{(stat)}\,^{+0.8}_{-0.7}\,\textrm{(syst)}\textrm{pb}$ and $\sigma(\textrm{VBF}$ $H\rightarrow WW^\ast) = 0.51\,^{+0.17}_{-0.15}\,\textrm{(stat)}\,^{+0.13}_{-0.08}\,\textrm{(syst)}\textrm{pb}$. The fiducial cross section is determined for the gluon-fusion process in exclusive final states with zero or one associated jet.
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