Browsing by Author "Aad, G."
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Item ATLAS b-jet identification performance and efficiency measurement with tt¯ events in pp collisions at s√=13 TeV(The European Physical Journal C, 2019) Aad, G.; Abbott, B.; Abbott, D.C.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; et al.The algorithms used by the ATLAS Collaboration during Run 2 of the Large Hadron Collider to identify jets containing b-hadrons are presented. The performance of the algorithms is evaluated in the simulation and the efficiency with which these algorithms identify jets containing b-hadrons is measured in collision data. The measurement uses a likelihood-based method in a sample highly enriched in tt¯ events. The topology of the t→Wb decays is exploited to simultaneously measure both the jet flavour composition of the sample and the efficiency in a transverse momentum range from 20 to 600 GeV. The efficiency measurement is subsequently compared with that predicted by the simulation. The data used in this measurement, corresponding to a total integrated luminosity of 80.5 fb−1, were collected in proton–proton collisions during the years 2015–2017 at a centre-of-mass energy s√= 13 TeV. By simultaneously extracting both the efficiency and jet flavour composition, this measurement significantly improves the precision compared to previous results, with uncertainties ranging from 1 to 8% depending on the jet transverse momentum.Item Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at s√ = 8 TeV(Journal of High Energy Physics, 2020) Aad, G.; Abbott, B.; Abbott, D.C.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Carlson, Evan Michael; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb−1 for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (F0), left-handed (FL), or right-handed (FR) polarizations. The resulting combined measurements of the polarization fractions are F0 = 0.693 ± 0.014 and FL = 0.315 ± 0.011. The fraction FR is calculated from the unitarity constraint to be FR = −0.008 ± 0.007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F0 (FL) with respect to the most precise single measurement. A limit on anomalous right-handed vector (VR), and left- and right-handed tensor (gL, gR) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [−0.11, 0.16] for VR, [−0.08, 0.05] for gL, and [−0.04, 0.02] for gR, at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived.Item Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at s√ = 8 TeV(Journal of High Energy Physics, 2020) Aad, G.; Abbott, B.; Abbott, D.C.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Carlson, Evan Michael; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb−1 for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (F0), left-handed (FL), or right-handed (FR) polarizations. The resulting combined measurements of the polarization fractions are F0 = 0.693 ± 0.014 and FL = 0.315 ± 0.011. The fraction FR is calculated from the unitarity constraint to be FR = −0.008 ± 0.007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F0 (FL) with respect to the most precise single measurement. A limit on anomalous right-handed vector (VR), and left- and right-handed tensor (gL, gR) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [−0.11, 0.16] for VR, [−0.08, 0.05] for gL, and [−0.04, 0.02] for gR, at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived.Item Combinations of single-top-quark production cross-section measurements and |fLVVtb| determinations at √s = 7 and 8 TeV with the ATLAS and CMS experiments(Journal of High Energy Physics, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abed Abud, A.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S; Abraham, N.L; Albert, J; Anelli, C. R; Chiu, Y. H; Ghasemi Bostanabad, M; Hamano, K; Hill, E; Kay, E. F; Keeler, R; Kowalewski, R; Lefebvre, M; et al.This paper presents the combinations of single-top-quark production crosssection 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: tchannel, 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 schannel cross-section, the combination yields 4.9 ± 1.4 pb at √ s = 8 TeV. The square of the magnitude of the CKM matrix element Vtb 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 |Vtd|, |Vts| |Vtb|. All the |fLVVtb| 2 determinations, extracted from individual ratios at √ s = 7 and 8 TeV, are combined, resulting in |fLVVtb| = 1.02 ± 0.04 (meas.) ± 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions.Item Constraints on mediator-based dark matter and scalar dark energy models using √s = 13 TeV pp collision data collected by the ATLAS detector(Journal of High Energy Physics, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; et al.Constraints on selected mediator-based dark matter models and a scalar dark energy model using up to 37 fb−1 s√=13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015-2016 are summarised in this paper. The results of experimental searches in a variety of final states are interpreted in terms of a set of spin-1 and spin-0 single-mediator dark matter simplified models and a second set of models involving an extended Higgs sector plus an additional vector or pseudo-scalar mediator. The searches considered in this paper constrain spin-1 leptophobic and leptophilic mediators, spin-0 colour-neutral and colour-charged mediators and vector or pseudo-scalar mediators embedded in extended Higgs sector models. In this case, also s√=8 TeV pp collision data are used for the interpretation of the results. The results are also interpreted for the first time in terms of light scalar particles that could contribute to the accelerating expansion of the universe (dark energy).Item Electron reconstruction and identification in the ATLAS experiment using the 2015 and 2016 LHC proton–proton collision data at √s =13 TeV(The European Physical Journal C, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Albert, Justin; Anelli, Christopher R.; Chiu, Y.H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.Algorithms used for the reconstruction and identification of electrons in the central region of the ATLAS detector at the Large Hadron Collider (LHC) are presented in this paper; these algorithms are used in ATLAS physics analyses that involve electrons in the final state and which are based on the 2015 and 2016 proton–proton collision data produced by the LHC at s√ = 13 TeV. The performance of the electron reconstruction, identification, isolation, and charge identification algorithms is evaluated in data and in simulated samples using electrons from Z→ee and J/ψ→ee decays. Typical examples of combinations of electron reconstruction, identification, and isolation operating points used in ATLAS physics analyses are shown.Item Erratum to: Measurement of differential cross sections and W+/W− cross-section ratios for W boson production in association with jets at s√ = 8 TeV with the ATLAS detector(Journal of High Energy Physics, 2020) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, M.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; et al.Item Erratum to: Measurement of differential cross sections for single diffractive dissociation in √s = 8 TeV pp collisions using the ATLAS ALFA spectrometer(Journal of High Energy Physics, 2020) Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Albert, Justin; Anelli, Christopher R.; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; Lefebvre, M.; et al.Item Erratum to: Measurement of the W boson polarisation in tt¯ events from pp collisions at s√=8 TeV in the lepton + jets channel with ATLAS(The European Physical Journal C, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Abeloos, B.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Albert, Justin; Elliot, Alison A.; Fincke-Keeler, M.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; et al.Item Erratum to: Measurements of W and Z boson production in pp collisions at s√=5.02 TeV with the ATLAS detector(The European Physical Journal C, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Chiu, Y.H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; McLean, K.D.; et al.Item Erratum to: Search for diboson resonances in hadronic final states in 139 fb−1 of pp collisions at √s = 13 TeV with the ATLAS detector(Journal of High Energy Physics, 2020) Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Albert, Justin; Anelli, Christopher R.; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.Item Erratum: Search for supersymmetry in final states with two same-sign or three leptons and jets using 36 fb−1 of √ s = 13 TeV pp collision data with the ATLAS detector(Journal of High Energy Physics, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; et al.Item Fluctuations of anisotropic flow in Pb+Pb collisions at √sNN= 5.02 TeV with the ATLAS detector(Journal of High Energy Physics, 2020) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abed Abud, A.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Albert, Justin; Anelli, Christopher R.; Carlson, Evan Michael; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.Multi-particle azimuthal cumulants are measured as a function of centrality and transverse momentum using 470 μb−1 of Pb+Pb collisions at sNN−−−√ = 5.02 TeV with the ATLAS detector at the LHC. These cumulants provide information on the event-by-event fluctuations of harmonic flow coefficients vn and correlated fluctuations between two harmonics vn and vm. For the first time, a non-zero four-particle cumulant is observed for dipolar flow, v1. The four-particle cumulants for elliptic flow, v2, and triangular flow, v3, exhibit a strong centrality dependence and change sign in ultra-central collisions. This sign change is consistent with significant non-Gaussian fluctuations in v2 and v3. The four-particle cumulant for quadrangular flow, v4, is found to change sign in mid-central collisions. Correlations between two harmonics are studied with three- and four-particle mixed-harmonic cumulants, which indicate an anti-correlation between v2 and v3, and a positive correlation between v2 and v4. These correlations decrease in strength towards central collisions and either approach zero or change sign in ultra-central collisions. To investigate the possible flow fluctuations arising from intrinsic centrality or volume fluctuations, the results are compared between two different event classes used for centrality definitions. In peripheral and mid-central collisions where the cumulant signals are large, only small differences are observed. In ultra-central collisions, the differences are much larger and transverse momentum dependent. These results provide new information to disentangle flow fluctuations from the initial and final states, as well as new insights on the influence of centrality fluctuations.Item Identification of boosted Higgs bosons decaying into b-quark pairs with the ATLAS detector at 13 TeV(The European Physical Journal C, 2019) Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Albert, Justin; Anelli, Christopher R.; Chiu, Y.H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, H→bb¯, for proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy s√=13 TeV. These decays are reconstructed from calorimeter jets found with the anti-kt R=1.0 jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of R=0.2 track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb−1 of data collected in 2015 and 2016 using g→bb¯ and Z(→bb¯)γ event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties.Item In situ calibration of large-radius jet energy and mass in 13 TeV proton–proton collisions with the ATLAS detector(The European Physical Journal C, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.The response of the ATLAS detector to large-radius jets is measured in situ using 36.2 fb−1 of s√=13 TeV proton–proton collisions provided by the LHC and recorded by the ATLAS experiment during 2015 and 2016. The jet energy scale is measured in events where the jet recoils against a reference object, which can be either a calibrated photon, a reconstructed Z boson, or a system of well-measured small-radius jets. The jet energy resolution and a calibration of forward jets are derived using dijet balance measurements. The jet mass response is measured with two methods: using mass peaks formed by W bosons and top quarks with large transverse momenta and by comparing the jet mass measured using the energy deposited in the calorimeter with that using the momenta of charged-particle tracks. The transverse momentum and mass responses in simulations are found to be about 2–3% higher than in data. This difference is adjusted for with a correction factor. The results of the different methods are combined to yield a calibration over a large range of transverse momenta (pT). The precision of the relative jet energy scale is 1–2% for 200 GeV < pT < 2 TeV, while that of the mass scale is 2–10%. The ratio of the energy resolutions in data and simulation is measured to a precision of 10–15% over the same pT range.Item Measurement of differential cross sections for single diffractive dissociation in s√ = 8 TeV pp collisions using the ATLAS ALFA spectrometer(Journal of High Energy Physics, 2020) Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Albert, Justin; Anelli, Christopher R.; Chiu, Y.H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Richard; Lefebvre, Michel; et al.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 → 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 < log10ξ < −1.6 and 0.016 < |t| < 0.43 GeV2, where ξ 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 ξ, t, and ∆η, a variable that characterises the rapidity gap separating the proton and the system X . The data are consistent with an exponential t dependence, dσ/dt ∝ eBt with slope parameter B = 7.65 ± 0.34 GeV−2. Interpreted in the framework of triple Regge phenomenology, the ξ dependence leads to a pomeron intercept of α(0) = 1.07 ± 0.09.Item Measurement of distributions sensitive to the underlying event in inclusive Z boson production in pp collisions at s√ = 13 TeV with the ATLAS detector(The European Physical Journal C, 2019) Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Albert, Justin; Anelli, Christopher R.; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; et al.This paper presents measurements of charged-particle distributions sensitive to the properties of the underlying event in events containing a Z boson decaying into a muon pair. The data were obtained using the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of 13 TeV with an integrated luminosity of 3.2 fb −1. Distributions of the charged-particle multiplicity and of the charged-particle transverse momentum are measured in regions of the azimuth defined relative to the Z boson direction. The measured distributions are compared with the predictions of various Monte Carlo generators which implement different underyling event models. The Monte Carlo model predictions qualitatively describe the data well, but with some significant discrepancies.Item Measurement of fiducial and differential W+W− production cross-sections at s√=13 TeV with the ATLAS detector(The European Physical Journal C, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abed Abud, A.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Albert, Justin; Anelli, Christopher R.; Chiu, Y.H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; et al.A measurement of fiducial and differential cross-sections for W+W− production in proton–proton collisions at s√=13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 36.1 fb−1 is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as WW→e±νμ∓ν. To suppress top-quark background, events containing jets with a transverse momentum exceeding 35 GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory.Item Measurement of flow harmonics correlations with mean transverse momentum in lead–lead and proton–lead collisions at sNN−−−√=5.02 TeV with the ATLAS detector(The European Physical Journal C, 2019) Aad, G.; Abbott, B.; Abbott, D.C.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Chiu, Y.H.; Ghasemi Bostanabad, M.; Hamano, K.; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.To assess the properties of the quark–gluon plasma formed in ultrarelativistic ion collisions, the ATLAS experiment at the LHC measures a correlation between the mean transverse momentum and the flow harmonics. The analysis uses data samples of lead–lead and proton–lead collisions obtained at the centre-of-mass energy per nucleon pair of 5.02 TeV, corresponding to total integrated luminosities of 22 μb−1 and 28 nb−1, respectively. The measurement is performed using a modified Pearson correlation coefficient with the charged-particle tracks on an event-by-event basis. The modified Pearson correlation coefficients for the 2nd-, 3rd-, and 4th-order flow harmonics are measured in the lead–lead collisions as a function of event centrality quantified as the number of charged particles or the number of nucleons participating in the collision. The measurements are performed for several intervals of the charged-particle transverse momentum. The correlation coefficients for all studied harmonics exhibit a strong centrality evolution, which only weakly depends on the charged-particle momentum range. In the proton–lead collisions, the modified Pearson correlation coefficient measured for the 2nd-order flow harmonics shows only weak centrality dependence. The lead-lead data is qualitatively described by the predictions based on the hydrodynamical model.Item Measurement of isolated-photon plus two-jet production in pp collisions at s√ = 13 TeV with the ATLAS detector(Journal of High Energy Physics, 2020) Aad, G.; Abbott, B.; Abbott, D.C.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Chiu, Y.H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.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, γ + 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.