ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Luminosity determination in pp collisions at √s=13 TeV using the ATLAS detector at the LHC. Eur. Phys. J. C, 83(10), 982–67pp.
Abstract: The luminosity determination for the ATLAS detector at the LHC during Run 2 is presented, with pp collisions at a centre-of-mass energy root s = 13TeV. The absolute luminosity scale is determined using van der Meer beam separation scans during dedicated running periods in each year, and extrapolated to the physics data-taking regime using complementary measurements from several luminosity-sensitive detectors. The total uncertainties in the integrated luminosity for each individual year of datataking range from 0.9% to 1.1%, and are partially correlated between years. After standard data-quality selections, the full Run 2 pp data sample corresponds to an integrated luminosity of 140.1 +/- 1.2fb(-1), i.e. an uncertainty of 0.83%. A dedicated sample of low-pileup data recorded in 2017-2018 for precision Standard Model physics measurements is analysed separately, and has an integrated luminosity of 338.1 +/- 3.1pb(-1).
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Measurement of the Higgs boson mass in the H→ZZ∗→4ℓ decay channel using 139 fb−1 of √s=13 TeV pp collisions recorded by the ATLAS detector at the LHC. Phys. Lett. B, 843, 137880–23pp.
Abstract: The mass of the Higgs boson is measured in the H→ZZ∗→4ℓ decay channel. The analysis uses proton-proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of 139 fb−1. The measured value of the Higgs boson mass is 124.99±0.18(stat.)±0.04(syst.) GeV and is based on improved momentum-scale calibration for muons relative to previous publications. The measurement also employs an analytic model that takes into account the invariant-mass resolution of the four-lepton system on a per-event basis and the output of a deep neural network discriminating signal from background events. This measurement is combined with the corresponding measurement using 7 and 8 TeV pp collision data, resulting in a Higgs boson mass measurement of 124.94±0.17(stat.)±0.03(syst.) GeV.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2023). Measurement of the Higgs boson mass with H→γγ decays in 140 fb−1 of √s=13 TeV pp collisions with the ATLAS detector. Phys. Lett. B, 847, 138315–23pp.
Abstract: The mass of the Higgs boson is measured in the H→γγ decay channel, exploiting the high resolution of the invariant mass of photon pairs reconstructed from the decays of Higgs bosons produced in proton-proton collisions at a centre-of-mass energy s√=13 TeV. The dataset was collected between 2015 and 2018 by the ATLAS detector at the Large Hadron Collider, and corresponds to an integrated luminosity of 140 fb−1. The measured value of the Higgs boson mass is 125.17±0.11(stat.)±0.09(syst.) GeV and is based on an improved energy scale calibration for photons, whose impact on the measurement is about four times smaller than in the previous publication. A combination with the corresponding measurement using 7 and 8 TeV pp collision ATLAS data results in a Higgs boson mass measurement of 125.22±0.11(stat.)±0.09(syst.) GeV. With an uncertainty of 1.1 per mille, this is currently the most precise measurement of the mass of the Higgs boson from a single decay channel.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Measurement of the total and differential Higgs boson production cross-sections at root s=13 TeV with the ATLAS detector by combining the H -> ZZ(*)-> 4l and H -> gamma gamma decay channels. J. High Energy Phys., 05(5), 028–42pp.
Abstract: The total and differential Higgs boson production cross-sections are measured through a combined statistical analysis of the H -> ZZ(*) -> 4l and H -> gamma gamma decay channels. The results are based on a dataset of 139 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13 TeV, recorded by the ATLAS detector at the Large Hadron Collider. The measured total Higgs boson production cross-section is 55.5(-3.8)(+4.0) pb, consistent with the Standard Model prediction of 55.6 +/- 2.5 pb. All results from the two decay channels are compatible with each other, and their combination agrees with the Standard Model predictions. A combined statistical interpretation of the measured fiducial cross-sections as a function of the Higgs boson transverse momentum is performed in order to probe the Yukawa couplings to the bottom and charm quarks. A similar interpretation is performed by including also the constraints from the measurements of Higgs boson production in association with a W or Z boson in the H -> b (b) over bar and c (c) over bar decay channels.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Integrated and differential fiducial cross-section measurements for the vector boson fusion production of the Higgs boson in the H → WW* → eνμν decay channel at 13 TeV with the ATLAS detector. Phys. Rev. D, 108(7), 072003–52pp.
Abstract: The vector-boson production cross section for the Higgs boson decay in the H -> WW* -> e nu μnu channel is measured as a function of kinematic observables sensitive to the Higgs boson production and decay properties as well as integrated in a fiducial phase space. The analysis is performed using the proton-proton collision data collected by the ATLAS detector in Run 2 of the LHC at root s = 13 TeV center-of-mass energy, corresponding to an integrated luminosity of 139 fb(-1). The different flavor final state is studied by selecting an electron and a muon originating from a pair of W bosons and compatible with the Higgs boson decay. The data are corrected for the effects of detector inefficiency and resolution, and the measurements are compared with different state-of-the-art theoretical predictions. The differential cross sections are used to constrain anomalous interactions described by dimension-six operators in an effective field theory.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Measurement of Suppression of Large-Radius Jets and Its Dependence on Substructure in Pb+Pb Collisions at sqrt[s_{NN}]=5.02TeV with the ATLAS Detector. Phys. Rev. Lett., 131(17), 172301–22pp.
Abstract: This letter presents a measurement of the nuclear modification factor of large-radius jets in root sNN=5.02 TeV Pb+Pb collisions by the ATLAS experiment. The measurement is performed using 1.72nb^{-1} and 257pb^{-1} of Pb+Pb and pp data, respectively. The large-radius jets are reconstructed with the anti-k{t} algorithm using a radius parameter of R=1.0, by reclustering anti-k{t} R=0.2 jets, and are measured over the transverse momentum (p{T}) kinematic range of 158<p{T}<1000GeV and absolute pseudorapidity |y|<2.0. The large-radius jet constituents are further reclustered using the k{t} algorithm in order to obtain the splitting parameters, sqrt[d{12}] and DeltaR{12}, which characterize the transverse momentum scale and angular separation for the hardest splitting in the jet, respectively. The nuclear modification factor, R{AA}, obtained by comparing the Pb+Pb jet yields to those in pp collisions, is measured as a function of jet transverse momentum (p{T}) and sqrt[d{12}] or DeltaR{12}. A significant difference in the quenching of large-radius jets having single subjet and those with more complex substructure is observed. Systematic comparison of jet suppression in terms of R{AA} for different jet definitions is also provided. Presented results support the hypothesis that jets with hard internal splittings lose more energy through quenching and provide a new perspective for understanding the role of jet structure in jet suppression.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Search for the Zy decay mode of new high-mass resonances in pp collisions at √s=13 TeV with the ATLAS detector. Phys. Lett. B, 848, 138394–23pp.
Abstract: This letter presents a search for narrow, high-mass resonances in the Zy final state with the Z boson decaying into a pair of electrons or muons. The root s = 13 TeV pp collision data were recorded by the ATLAS detector at the CERN Large Hadron Collider and have an integrated luminosity of 140 fb-1. The data are found to be in agreement with the Standard Model background expectation. Upper limits are set on the resonance production cross section times the decay branching ratio into Zy. For spin-0 resonances produced via gluon-gluon fusion, the observed limits at 95% confidence level vary between 65.5 fb and 0.6 fb, while for spin-2 resonances produced via gluon-gluon fusion (or quark-antiquark initial states) limits vary between 77.4 (76.1) fb and 0.6 (0.5) fb, for the mass range from 220 GeV to 3400 GeV.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Study of High-Transverse-Momentum Higgs Boson Production in Association with a Vector Boson in the qqbb Final State with the ATLAS Detector. Phys. Rev. Lett., 132(13), 131802–23pp.
Abstract: This Letter presents the first study of Higgs boson production in association with a vector boson (V = W or Z) in the fully hadronic qqbb final state using data recorded by the ATLAS detector at the LHC in ffiffiproton-proton collisions at root root s= 13 TeV and corresponding to an integrated luminosity of 137fb(-1). The vector bosons and Higgs bosons are each reconstructed as large-radius jets and tagged using jet substructure techniques. Dedicated tagging algorithms exploiting b-tagging properties are used to identify jets consistent with Higgs bosons decaying into b (b) over bar. Dominant backgrounds from multijet production are determined directly from the data, and a likelihood fit to the jet mass distribution of Higgs boson candidates is used to extract the number of signal events. The VH production cross section is measured inclusively and differentially in several ranges of Higgs boson transverse momentum: 250-450, 450-650, and greater than 650 GeV. The inclusive signal yield relative to the standard model expectation is observed to be μ= 1.4(-0.9)(+1.0) and the corresponding cross section is 3.1 +/- 1.3(stat)(-1.4)(+1.8) (syst) pb.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2023). Measurement of the cross-sections of the electroweak and total production of a Zγ pair in association with two jets in pp collisions at √s= 13 TeV with the ATLAS detector. Phys. Lett. B, 846, 138222–30pp.
Abstract: This Letter presents the measurement of the fiducial and differential cross-sections of the electroweak production of a Zγ pair in association with two jets. The analysis uses 140 fb−1 of LHC proton-proton collision data taken at s√=13 TeV recorded by the ATLAS detector during the years 2015-2018. Events with a Z boson candidate decaying into either an e+e− or μ+μ− pair, a photon and two jets are selected. The electroweak component is extracted by requiring a large dijet invariant mass and a large rapidity gap between the two jets and is measured with an observed and expected significance well above five standard deviations. The fiducial pp→Zγjj cross-section for the electroweak production is measured to be 3.6 ± 0.5 fb. The total fiducial cross-section that also includes contributions where the jets arise from strong interactions is measured to be 16.8+2.0−1.8 fb. The results are consistent with the Standard Model predictions. Differential cross-sections are also measured using the same events and are compared with parton-shower Monte Carlo simulations. Good agreement is observed between data and predictions.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Evidence of off-shell Higgs boson production from ZZ leptonic decay channels and constraints on its total width with the ATLAS detector. Phys. Lett. B, 846, 138223–29pp.
Abstract: This Letter reports on a search for off-shell production of the Higgs boson using 139 fb(-1) of pp collision data at root s = 13 TeV collected by the ATLAS detector at the Large Hadron Collider. The signature is a pair of Z bosons, with contributions from both the production and subsequent decay of a virtual Higgs boson and the interference of that process with other processes. The two observable final states are ZZ -> 4l and Z Z -> 2l2 nu with l = e or mu. In the ZZ -> 4l final state, a dense Neural Network is used to enhance analysis sensitivity with respect to matrix element-based discrimination. The background-only hypothesis is rejected with an observed (expected) significance of 3.3 (2.2) standard deviations, representing experimental evidence for off-shell Higgs boson production. Assuming that no new particles enter the production of the virtual Higgs boson, its total width can be deduced from the measurement of its off-shell production cross-section. The measured total width of the Higgs boson is 4.5(-2.5)(+3.3) MeV, and the observed (expected) upper limit on the total width is found to be 10.5 (10.9) MeV at 95% confidence level.
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