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Träfflista för sökning "LAR1:uu ;pers:(Aad G);srt2:(2020)"

Sökning: LAR1:uu > Aad G > (2020)

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1.
  • Aad, G., et al. (författare)
  • Combination of searches for Higgs boson pairs in pp collisions at root s=13 TeV with the ATLAS detector
  • 2020
  • Ingår i: Physics Letters B. - ELSEVIER. - 0370-2693 .- 1873-2445. ; 800
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb(-1) of proton-proton collision data at a centre-of-mass energy root s = 13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the b (b) over barb (b) over bar, b (b) over barW(+)W(-), b (b) over bar tau(+)tau(-), W+W-W+W-, b (b) over bar gamma gamma and W+W-gamma gamma final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) times the predicted Standard Model cross-section. Limits are also set on the ratio (kappa(lambda)) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level in observation (expectation) to -5.0 &lt; kappa(lambda) &lt; 12.0 (-5.8 &lt; kappa(lambda) &lt; 12.0). In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza-Klein Randall-Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model. </p>
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2.
  • Aad, G., et al. (författare)
  • Evidence for electroweak production of two jets in association with a Zγ pair in <em>pp</em> collisions at √<em>S</em>=13 TeV with the ATLAS detector
  • 2020
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 803
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Evidence for electroweak production of two jets in association with a Z gamma pair in root s = 13 TeV proton-proton collisions at the Large Hadron Collider is presented. The analysis uses data collected by the ATLAS detector in 2015 and 2016 that corresponds to an integrated luminosity of 36.1 fb(-1). Events that contain a Z boson candidate decaying leptonically into either e(+)e(-) or mu(+)mu(-), a photon, and two jets are selected. The electroweak component is measured with observed and expected significances of 4.1 standard deviations. The fiducial cross-section for electroweak production is measured to be sigma(Z gamma jj-Ew) = 7.8 +/- 2.0 fb, in good agreement with the Standard Model prediction.</p>
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3.
  • Aad, G., et al. (författare)
  • Measurement of differential cross sections for single diffractive dissociation in root s=8 TeV pp collisions using the ATLAS ALFA spectrometer
  • 2020
  • Ingår i: Journal of High Energy Physics (JHEP). - SPRINGER. - 1126-6708 .- 1029-8479. ; :2
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy s= 8 TeV is used to study inclusive single diffractive dissociation, pp -&gt; X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is -4.0 &lt; log(10)xi &lt; -1.6 and 0.016 &lt; |t| &lt; 0.43 GeV2, where xi is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 +/- 0.13 mb. Cross sections are also measured differentially as functions of xi, t, and increment eta, a variable that characterises the rapidity gap separating the proton and the system X . The data are consistent with an exponential t dependence, d sigma/dt proportional to e(Bt) with slope parameter B = 7.65 +/- 0.34 GeV-2. Interpreted in the framework of triple Regge phenomenology, the xi dependence leads to a pomeron intercept of alpha(0) = 1.07 +/- 0.09.</p>
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4.
  • Aad, G., et al. (författare)
  • Measurement of isolated-photon plus two-jet production in pp collisions at <em>√s</em>=13 TeV with the ATLAS detector
  • 2020
  • Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :3
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The dynamics of isolated-photon plus two-jet production in pp collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset corresponding to an integrated luminosity of 36.1 fb(-1). Cross sections are measured as functions of a variety of observables, including angular correlations and invariant masses of the objects in the final state, gamma + jet + jet. Measurements are also performed in phase-space regions enriched in each of the two underlying physical mechanisms, namely direct and fragmentation processes. The measurements cover the range of photon (jet) transverse momenta from 150 GeV (100 GeV) to 2 TeV. The tree-level plus parton-shower predictions from Sherpa and Pythia as well as the next-to-leading-order QCD predictions from Sherpa are compared with the measurements. The next-to-leading-order QCD predictions describe the data adequately in shape and normalisation except for regions of phase space such as those with high values of the invariant mass or rapidity separation of the two jets, where the predictions overestimate the data.</p>
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5.
  • Aad, G., et al. (författare)
  • Measurement of soft-drop jet observables in pp collisions with the ATLAS detector at root s=13 TeV
  • 2020
  • Ingår i: Physical Review D : covering particles, fields, gravitation, and cosmology. - AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 101:5
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Jet substructure quantities are measured using jets groomed with the soft-drop grooming procedure in dijet events from 32.9 fb(-1) of pp collisions collected with the ATLAS detector at root s = 13 TeV. These observables are sensitive to a wide range of QCD phenomena. Some observables, such as the jet mass and opening angle between the two subjets which pass the soft-drop condition, can be described by a high-order (resummed) series in the strong coupling constant alpha(s). Other observables, such as the momentum sharing between the two subjets, are nearly independent of alpha(s). These observables can be constructed using all interacting particles or using only charged particles reconstructed in the inner tracking detectors. Track-based versions of these observables are not collinear safe, but are measured more precisely, and universal nonperturbative functions can absorb the collinear singularities. The unfolded data are directly compared with QCD calculations and hadron-level Monte Carlo simulations. The measurements are performed in different pseudorapidity regions, which are then used to extract quark and gluon jet shapes using the predicted quark and gluon fractions in each region. All of the parton shower and analytical calculations provide an excellent description of the data in most regions of phase space.</p>
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6.
  • Aad, G., et al. (författare)
  • Measurement of the azimuthal anisotropy of charged-particle production in Xe plus Xe collisions at root S-NN=5.44 TeV with the ATLAS detector
  • 2020
  • Ingår i: Physical Review C : Covering Nuclear Physics. - AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 101:2
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>This paper describes the measurements of flow harmonics v(2)-v(6) in 3 mu b(-1) of Xe Xe collisions at root S-NN = 5.44 TeV performed using the ATLAS detector at the Large Hadron Collider (LHC). Measurements of the centrality, multiplicity, and p(T) dependence of the v(n) obtained using two-particle correlations and the scalar product technique are presented. The measurements are also performed using a template-fit procedure, which was developed to remove nonflow correlations in small collision systems. This nonflow removal is shown to have a significant influence on the measured v(n) at high p(T), especially in peripheral events. Comparisons of the measured v(n) with measurements in Pb + Pb collisions and p + Pb collisions at root S-NN = 5.02 TeV are also presented. The v(n) values in Xe + Xe collisions are observed to be larger than those in Pb + Pb collisions for n = 2, 3, and 4 in the most central events. However, with decreasing centrality or increasing harmonic order n, the v(n) values in Xe + Xe collisions become smaller than those in Pb + Pb collisions. The v(n) in Xe + Xe and Pb + Pb collisions are also compared as a function of the mean number of participating nucleons, &lt; N-part &gt;, and the measured charged-particle multiplicity in the detector. The v(3) values in Xe + Xe and Pb + Pb collisions are observed to be similar at the same &lt; N-part &gt; or multiplicity, but the other harmonics are significantly different. The ratios of the measured v(n) in Xe + Xe and Pb + Pb collisions, as a function of centrality, are also compared to theoretical calculations.</p>
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7.
  • Aad, G., et al. (författare)
  • Measurement of the Lund Jet Plane Using Charged Particles in 13 TeV Proton-Proton Collisions with the ATLAS Detector
  • 2020
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 124:22
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The prevalence of hadronic jets at the LHC requires that a deep understanding of jet formation and structure is achieved in order to reach the highest levels of experimental and theoretical precision. There have been many measurements of jet substructure at the LHC and previous colliders, but the targeted observables mix physical effects from various origins. Based on a recent proposal to factorize physical effects, this Letter presents a double-differential cross-section measurement of the Lund jet plane using 139 fb(-1) of root s = 13 TeV proton-proton collision data collected with the ATLAS detector using jets with transverse momentum above 675 GeV. The measurement uses charged particles to achieve a fine angular resolution and is corrected for acceptance and detector effects. Several parton shower Monte Carlo models are compared with the data. No single model is found to be in agreement with the measured data across the entire plane.</p>
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8.
  • Aad, G., et al. (författare)
  • Measurement of the Z(-&gt; l(+)l(-))gamma production cross-section in pp collisions at root s=13 TeV with the ATLAS detector
  • 2020
  • Ingår i: Journal of High Energy Physics (JHEP). - SPRINGER. - 1126-6708 .- 1029-8479. ; :3
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The production of a prompt photon in association with a Z boson is studied in proton-proton collisions at a centre-of-mass energy s = 13 TeV. The analysis uses a data sample with an integrated luminosity of 139 fb(-1) collected by the ATLAS detector at the LHC from 2015 to 2018. The production cross-section for the process pp -&gt; l(+)l(-)gamma + X (l = e, mu) is measured within a fiducial phase-space region defined by kinematic requirements on the photon and the leptons, and by isolation requirements on the photon. An experimental precision of 2.9% is achieved for the fiducial cross-section. Differential cross-sections are measured as a function of each of six kinematic variables characterising the l(+)l(-)gamma system. The data are compared with theoretical predictions based on next-to-leading-order and next-to-next-to-leading-order perturbative QCD calculations. The impact of next-to-leading-order electroweak corrections is also considered.</p>
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9.
  • Aad, G., et al. (författare)
  • Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in <em>√s=13 TeV pp</em> collisions with the ATLAS detector
  • 2020
  • Ingår i: Physical Review D : covering particles, fields, gravitation, and cosmology. - 2470-0010 .- 2470-0029. ; 101:7
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of root s = 13 TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015-2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV.</p>
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10.
  • Aad, G., et al. (författare)
  • Search for direct stau production in events with two hadronic tau-leptons in root s=13 TeV pp collisions with the ATLAS detector
  • 2020
  • Ingår i: Physical Review D : covering particles, fields, gravitation, and cosmology. - AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 101:3
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>A search for the direct production of the supersymmetric partners of tau-leptons (staus) in final states with two hadronically decaying tau-leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of 139 fb(-1), recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of direct production of stau pairs with each stau decaying into the stable lightest neutralino and one tau-lepton in simplified models where the two stau mass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidence level for a massless lightest neutralino.</p>
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