6,804 research outputs found
Measurement of W ± Z production in proton-proton collisions at sâ=7 TeV with the ATLAS detector
A study of W ± Z production in proton-proton collisions at sâ=7 TeV is presented using data corresponding to an integrated luminosity of 4.6 fbâ1 collected with the ATLAS detector at the Large Hadron Collider in 2011. In total, 317 candidates, with a background expectation of 68±10 events, are observed in double-leptonic decay final states with electrons, muons and missing transverse momentum. The total cross-section is determined to be ÏtotWZ=19.0+1.4â1.3(stat.)±0.9(syst.)±0.4(lumi.) pb , consistent with the Standard Model expectation of 17.6+1.1â1.0 pb . Limits on anomalous triple gauge boson couplings are derived using the transverse momentum spectrum of Z bosons in the selected events. The cross-section is also presented as a function of Z boson transverse momentum and diboson invariant mass
Measurement of the inclusive isolated prompt photon cross section in pp collisions at root s=7 TeV with the ATLAS detector
A measurement of the cross section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy root s = 7 TeV is presented. The measurement covers the pseudorapidity ranges vertical bar eta(gamma)vertical bar < 1: 37 and 1: 52 <= vertical bar eta(gamma)vertical bar < 1: 81 in the transverse energy range 15 <= E-T(gamma) < 100 GeV. The results are based on an integrated luminosity of 880 nb(-1), collected with the ATLAS detector at the Large Hadron Collider. Photon candidates are identified by combining information from the calorimeters and from the inner tracker. Residual background in the selected sample is estimated from data based on the observed distribution of the transverse isolation energy in a narrow cone around the photon candidate. The results are compared to predictions from next-to-leading-order perturbative QCD calculations
Searches for heavy long-lived sleptons and R-hadrons with the ATLAS detector in pp collisions at âs=7 TeV
A search for long-lived particles is performed using a data sample of 4.7 fbâ1 from protonâproton collisions at a centre-of-mass energy âs =7 TeV collected by the ATLAS detector at the LHC. No excess is observed above the estimated background and lower limits, at 95% conïŹdence level, are set on the mass of the long-lived particles in different scenarios, based on their possible interactions in the inner detector, the calorimeters and the muon spectrometer. Long-lived staus in gauge-mediated SUSY-breaking models are excluded up to a mass of 300 GeV for tanÎČ =5â20. Directly produced long-lived sleptons are excluded up to a mass of 278 GeV. R-hadrons, composites of gluino (stop, sbottom) and light quarks, are excluded up to a mass of 985 GeV (683 GeV, 612 GeV) when using a generic interaction model. Additionally two sets of limits on R-hadrons are obtained that are less sensitive to the interaction model for R-hadrons. One set of limits is obtained using only the inner detector and calorimeter observables, and a second set of limits is obtained based on the inner detector alone
Search for a standard model Higgs boson in the H -> ZZ -> l(+)l(-) nu(nu)over-bar decay channel using 4.7 fb(-1) of root s=7 TeV data with the ATLAS detector
A search for a Standard Model Higgs boson decaying via H -> ZZ -> l(+)l(-) nu(nu) over bar, where l represents electrons or muons, is presented. It is based on proton-proton collision data at root s = 7 TeV, collected by the ATLAS experiment at the LHC during 2011 and corresponding to an integrated luminosity of 4.7 fb(-1). The data agree with the expected Standard Model backgrounds. Upper limits on the Higgs boson production cross section are derived for Higgs boson masses between 200 GeV and 600 GeV and the production of a Standard Model Higgs boson with a mass in the range 319-558 GeV is excluded at the 95% confidence level
Search for contact interactions and large extra dimensions in dilepton events from pp collisions at sâ=7ââTeV with the ATLAS detector
A search for nonresonant new phenomena, originating from either contact interactions or large extra spatial dimensions, has been carried out using events with two isolated electrons or muons. These events, produced at the LHC in proton-proton collisions at sâ=7ââTeV, were recorded by the ATLAS detector. The data sample, collected throughout 2011, corresponds to an integrated luminosity of 4.9 and 5.0ââfbâ1 in the e+eâ and ÎŒ+ÎŒâ channels, respectively. No significant deviations from the Standard Model expectation are observed. Using a Bayesian approach, 95% confidence level lower limits ranging from 9.0 to 13.9 TeV are placed on the energy scale of ââqq contact interactions in the left-left isoscalar model. Lower limits ranging from 2.4 to 3.9 TeV are also set on the string scale in large extra dimension models. After combining these limits with results from a similar search in the diphoton channel, slightly more stringent limits are obtained
Search for a Standard Model Higgs boson in the mass range 200-600 GeV in the H -> ZZ -> l(+)l(-)q(q)over-bar decay channel with the ATLAS detector
A search for a heavy Standard Model Higgs boson decaying via H -> ZZ -> l(+)l(-)q (q) over bar, where l = e or mu, is presented. The search uses a data set of pp collisions at root s = 7 TeV, corresponding to an integrated luminosity of 4.7 fb(-1) collected in 2011 by the ATLAS detector at the CERN LHC. No significant excess of events above the estimated background is found. Upper limits at 95% confidence level on the production cross section of a Higgs boson with a mass in the range between 200 and 600 GeV are derived. A Standard Model Higgs boson with a mass in the range 300 GeV <= m(H) 322 <= GeV or 353 GeV <= m(H) <= 410 GeV is excluded at 95% CL The corresponding expected exclusion range is 351 GeV <= m(H) <= 404 GeV at 95% CL
Measurements of WÎł and ZÎł production in pp collisions at âs=7ââTeV with the ATLAS detector at the LHC
The integrated and differential fiducial cross sections for the production of a W or Z boson in association with a high-energy photon are measured using pp collisions at âs=7ââTeV. The analyses use a data sample with an integrated luminosity of 4.6ââfb-1 collected by the ATLAS detector during the 2011 LHC data-taking period. Events are selected using leptonic decays of the W and Z bosons [W(eÎœ,ΌΜ) and Z(e+e-,ÎŒ+ÎŒ-,ΜΜÌ
)] with the requirement of an associated isolated photon. The data are used to test the electroweak sector of the Standard Model and search for evidence for new phenomena. The measurements are used to probe the anomalous WWγ, ZZγ, and Zγγ triple-gauge-boson couplings and to search for the production of vector resonances decaying to Zγ and Wγ. No deviations from Standard Model predictions are observed and limits are placed on anomalous triple-gauge-boson couplings and on the production of new vector meson resonances
ATLAS search for new phenomena in dijet mass and angular distributions using pp collisions at sâ=7 TeV
Mass and angular distributions of dijets produced in LHC proton-proton collisions at a centre-of-mass energy sâ=7 TeV have been studied with the ATLAS detector using the full 2011 data set with an integrated luminosity of 4.8 fbâ1. Dijet masses up to ~ 4.0 TeV have been probed. No resonance-like features have been observed in the dijet mass spectrum, and all angular distributions are consistent with the predictions of QCD. Exclusion limits on six hypotheses of new phenomena have been set at 95% CL in terms of mass or energy scale, as appropriate. These hypotheses include excited quarks below 2.83 TeV, colour octet scalars below 1.86 TeV, heavy W bosons below 1.68 TeV, string resonances below 3.61 TeV, quantum black holes with six extra space-time dimensions for quantum gravity scales below 4.11 TeV, and quark contact interactions below a compositeness scale of 7.6 TeV in a destructive interference scenario
Combined search for the Standard Model Higgs boson in pp collisions at sâ=7ââTeV with the ATLAS detector
A combined search for the Standard Model Higgs boson with the ATLAS detector at the LHC is presented. The data sets used correspond to integrated luminosities from 4.6ââfbâ1 to 4.9ââfbâ1 of proton-proton collisions collected at sâ=7ââTeV in 2011. The Higgs boson mass ranges of 111.4 GeV to 116.6 GeV, 119.4 GeV to 122.1 GeV, and 129.2 GeV to 541 GeV are excluded at the 95% confidence level, while the range 120 GeV to 560 GeV is expected to be excluded in the absence of a signal. An excess of events is observed at Higgs boson mass hypotheses around 126 GeV with a local significance of 2.9 standard deviations (Ï). The global probability for the background to produce an excess at least as significant anywhere in the entire explored Higgs boson mass range of 110â600 GeV is estimated to be âŒ15%, corresponding to a significance of approximately 1Ï
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in root s=7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb(-1) of root s = 7 TeV proton-proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
- âŠ