5,069 research outputs found
Measurement of VH, H → bb̅ Production as a Function of the Vector-Boson Transverse Momentum in 13 TeV pp Collisions with the ATLAS Detector
No full textCross-sections of associated production of a Higgs boson decaying into bottomquark pairs and an electroweak gauge boson, W or Z, decaying into leptons are measured as a function of the gauge boson transverse momentum. The measurements are performed in kinematic fiducial volumes defined in the ‘simplified template cross-section’ framework. The results are obtained using 79.8 fb⁻¹ of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. All measurements are found to be in agreement with the Standard Model predictions, and limits are set on the parameters of an effective Lagrangian sensitive to modifications of the Higgs boson couplings to the electroweak gauge bosons. ©2019, The Author(s).School of Natural Sciences and Mathematic
Measurement of the Four-Lepton Invariant Mass Spectrum in 13 TeV Proton-Proton Collisions with the ATLAS Detector
No full textA measurement of the four-lepton invariant mass spectrum is made with the ATLAS detector, using an integrated luminosity of 36.1 fb⁻¹ of proton-proton collisions at √s = 13 TeV delivered by the Large Hadron Collider. The differential cross-section is measured for events containing two same-flavour opposite-sign lepton pairs. It exhibits a rich structure, with different mass regions dominated in the Standard Model by single Z boson production, Higgs boson production, and Z boson pair production, and non-negligible interference effects at high invariant masses. The measurement is compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. These calculations are used to interpret the data in terms of gg → ZZ → 4ℓ and Z → 4ℓ subprocesses, and to place constraints on a possible contribution from physics beyond the Standard Model. ©2019 The Author(s).School of Natural Sciences and Mathematic
Search for Higgs Boson Pair Production in the bb̅ WW* Decay Mode at √s = 13 TeV with the ATLAS Detector
No full textA search for Higgs boson pair production in the bb̅ WW* decay mode is performed in the bb̅ℓνqq final state using 36.1 fb⁻¹ of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. No evidence of events beyond the background expectation is found. Upper limits on the non-resonant pp → HH production cross section of 10 pb and on the resonant production cross section as a function of the HH invariant mass are obtained. Resonant production limits are set for scalar and spin-2 graviton hypotheses in the mass range 500 to 3000 GeV.©2019, The Author(s).Natural Sciences and Mathematic
Observation of Electroweak W^{±} Z Boson Pair Production in Association with Two Jets in pp Collisions at√s=13 TeV with the ATLAS Detector
No full textAn observation of electroweak W^{±} Z production in association with two jets in proton–proton collisions is presented. The data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of √s=13 TeV are used, corresponding to an integrated luminosity of 36.1 fb⁻¹. Events containing three identified leptons, either electrons or muons, and two jets are selected. The electroweak production of W^{±} Z bosons in association with two jets is measured with an observed significance of 5.3 standard deviations. A fiducial cross-section for electroweak production including interference effects and for a single leptonic decay mode is measured to be σ_{WZjj-EW} = 0.57{_{-0.13} ^{+0.14}} (stat.) {_{-0.06) ^{+0.07}} (syst.) fb. Total and differential fiducial cross-sections of the sum of W^{±} Zjj electroweak and strong productions for several kinematic observables are also measured. © 2019 The Author(s)School of Natural Sciences and Mathematic
Measurement of the Exclusive γγ → μ⁺μ⁻ Process in Proton-Proton Collisions at √s=13 TeV with the ATLAS Detector
No full textThe production of exclusive γγ → μ⁺μ⁻ events in proton-proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC, using data corresponding to an integrated luminosity of 3.2 fb⁻¹. The measurement is performed for a dimuon invariant mass of 12 GeV < m(μ⁺μ⁻) < 70 GeV. The integrated cross-section is determined within a fiducial acceptance region of the ATLAS detector and differential cross-sections are measured as a function of the dimuon invariant mass. The results are compared to theoretical predictions both with and without corrections for absorptive effects. © 2017 The Author(s). Published by Elsevier B.V.School of Natural Sciences and Mathematic
Combinations of Single-Top-Quark Production Cross-Section Measurements and |fLvV_{tb}| Determinations at √s = 7 and 8 TeV with the ATLAS and CMS Experiments
No full textThis paper presents the combinations of single-top-quark production cross-section measurements by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at √s = 7 and 8 TeV corresponding to integrated luminosities of 1.17 to 5.1 fb⁻¹ at √s = 7 TeV and 12.2 to 20.3 fb⁻¹ at √s = 8 TeV. These combinations are performed per centre-of-mass energy and for each production mode: t-channel, tW, and s-channel. The combined t-channel cross-sections are 67.5 ± 5.7 pb and 87.7 ± 5.8 pb at √s = 7 and 8 TeV respectively. The combined tW cross-sections are 16.3 ± 4.1 pb and 23.1 ± 3.6 pb at √s = 7 and 8 TeV respectively. For the s-channel cross-section, the combination yields 4.9 ± 1.4 pb at √s = 8 TeV. The square of the magnitude of the CKM matrix element V_{tb} multiplied by a form factor fLV is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction. It is assumed that the top-quark-related CKM matrix elements obey the relation |V_{td}|, |V_{ts}| ≪ |V_{tb}|. All the |fLVV_{tb}|² determinations, extracted from individual ratios at √s = 7 and 8 TeV, are combined, resulting in |fLVV_{tb}| = 1.02 ± 0.04 (meas.) ± 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions. © 2019, The Author(s).School of Natural Sciences and Mathematic
Search for Higgs Boson Pair Production in the WW*WW* Decay Channel Using ATLAS Data Recorded at √s = 13 TeV
No full textA search for a pair of neutral, scalar bosons with each decaying into two W bosons is presented using 36.1 fb⁻¹ of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. This search uses three production models: non-resonant and resonant Higgs boson pair production and resonant production of a pair of heavy scalar particles. Three final states, classified by the number of leptons, are analysed: two same-sign leptons, three leptons, and four leptons. No significant excess over the expected Standard Model backgrounds is observed. An observed (expected) 95% confidence-level upper limit of 160 (120) times the Standard Model prediction of non-resonant Higgs boson pair production cross-section is set from a combined analysis of the three final states. Upper limits are set on the production cross-section times branching ratio of a heavy scalar X decaying into a Higgs boson pair in the mass range of 260 GeV ≤ mχ ≤ 500 GeV and the observed (expected) limits range from 9.3 (10) pb to 2.8 (2.6) pb. Upper limits are set on the production cross-section times branching ratio of a heavy scalar Χ decaying into a pair of heavy scalars S for mass ranges of 280 GeV ≤ mχ ≤ 340 GeV and 135 GeV ≤ m_{S} ≤ 165 GeV and the observed (expected) limits range from 2.5 (2.5) pb to 0.16 (0.17) pb. © 2019, The Author(s).School of Natural Sciences and Mathematic
Search for Single Production of Vector-Like Quarks Decaying into Wb in pp Collisions at √s = 13 TeV with the ATLAS Detector
No full textA search for singly produced vector-like quarks Q, where Q can be either a T quark with charge +2/3 or a Y quark with charge −4/3, is performed in proton–proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 36.1 fb⁻¹, recorded with the ATLAS detector at the LHC in 2015 and 2016. The analysis targets Q → Wb decays where the W boson decays leptonically. No significant deviation from the expected Standard Model background is observed. Upper limits are set on the QWb coupling strength and the mixing between the Standard Model sector and a singlet T quark or a Y quark from a (B, Y) doublet or a (T, B, Y) triplet, taking into account the interference effects with the Standard Model background. The upper limits set on the mixing angle are as small as |sin θ_{L}| = 0.18 for a singlet T quark of mass 800 GeV, |sin θ_{R}| = 0.17 for a Y quark of mass 800 GeV in a (B, Y) doublet model and |sin θ_{L}| = 0.16 for a Y quark of mass 800 GeV in a (T, B, Y) triplet model. Within a (B, Y) doublet model, the limits set on the mixing parameter |sin θ_{R}| are comparable with the exclusion limits from electroweak precision observables in the mass range between about 900 GeV and 1250 GeV. © 2019, The Author(s).School of Natural Sciences and Mathematic
Measurements of Inclusive and Differential Fiducial Cross-Sections of tt̅ Production with Additional Heavy-Flavour Jets in Proton-Proton Collisions at √s=13 TeV with the ATLAS Detector
No full textThis paper presents measurements of tt¯ production in association with additional b-jets in pp collisions at the LHC at a centre-of-mass energy of 13 TeV. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb −1 . Fiducial cross-section measurements are performed in the dilepton and lepton-plus-jets tt¯ decay channels. Results are presented at particle level in the form of inclusive cross-sections of tt¯ final states with three and four b-jets as well as differential cross-sections as a function of global event properties and properties of b-jet pairs. The measured inclusive fiducial cross-sections generally exceed the tt¯ bb¯ predictions from various next-to-leading-order matrix element calculations matched to a parton shower but are compatible within the total uncertainties. The experimental uncertainties are smaller than the uncertainties in the predictions. Comparisons of state-of-the-art theoretical predictions with the differential measurements are shown and good agreement with data is found for most of them. ©2019 The Author(s).School of Natural Sciences and Mathematic
Search for Heavy Resonances Decaying into a W or Z Boson and a Higgs Boson in Final States with Leptons and B-Jets in 36 fb⁻¹ of √s=13 TeV pp Collisions with the ATLAS Detector
No full textA search is conducted for new resonances decaying into a W or Z boson and a 125 GeV Higgs boson in the νν̅bb̅, ℓ^±νbb̅, and ℓ⁺ℓ⁻bb̅ final states, where ℓ^± = e^± or μ^±, in pp collisions at √s=13 TeV. The data used correspond to a total integrated luminosity of 36.1 fb⁻¹ collected with the ATLAS detector at the Large Hadron Collider during the 2015 and 2016 data-taking periods. The search is conducted by examining the reconstructed invariant or transverse mass distributions of W h and Zh candidates for evidence of a localised excess in the mass range of 220 GeV up to 5 TeV. No significant excess is observed and the results are interpreted in terms of constraints on the production cross-section times branching fraction of heavy W′ and Z′ resonances in heavy-vector-triplet models and the CP-odd scalar boson A in two-Higgs-doublet models. Upper limits are placed at the 95% confidence level and range between 9.0 × 10⁻⁴ pb and 7.3 × 10⁻¹ pb depending on the model and mass of the resonance. © 2018, The Author(s).School of Natural Sciences and Mathematic
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