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A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of root s = 13 TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). The results are interpreted in the context of various R-parity-conserving models where squarks and gluinos are produced in pairs or in association and a neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.30 TeV for a simplified model containing only a gluino and the lightest neutralino, assuming the latter is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.85 TeV are excluded if the lightest neutralino is massless. These limits extend substantially beyond the region of supersymmetric parameter space excluded previously by similar searches with the ATLAS detector.

A bstract This article presents searches for the Zγ decay of the Higgs boson and for narrow high-mass resonances decaying to Z γ, exploiting Z boson decays to pairs of electrons or muons. The data analysis uses 36.1 fb −1 of pp collisions at s = 13 recorded by the ATLAS detector at the CERN Large Hadron Collider. The data are found to be consistent with the expected Standard Model background. The observed (expected — assuming Standard Model pp → H → Z γ production and decay) upper limit on the production cross section times the branching ratio for pp → H → Z γ is 6.6. (5.2) times the Standard Model prediction at the 95% confidence level for a Higgs boson mass of 125.09 GeV. In addition, upper limits are set on the production cross section times the branching ratio as a function of the mass of a narrow resonance between 250 GeV and 2.4 TeV, assuming spin-0 resonances produced via gluon-gluon fusion, and spin-2 resonances produced via gluon-gluon or quark-antiquark initial states. For high-mass spin-0 resonances, the observed (expected) limits vary between 88 fb (61 fb) and 2.8 fb (2.7 fb) for the mass range from 250 GeV to 2.4 TeV at the 95% confidence level.

A bstract A search for the exclusive decays of the Higgs and Z bosons to a ϕ or ρ meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of up to 35 . 6 fb −1 collected at s = 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson couplings to light quarks. No significant excess of events is observed above the background, as expected from the Standard Model. Upper limits at 95% confidence level were obtained on the branching fractions of the Higgs boson decays to ϕ γ and ρ γ of 4 . 8 × 10 −4 and 8 . 8 × 10 −4 , respectively. The corresponding 95% confidence level upper limits for the Z boson decays are 0 . 9 × 10 −6 and 25 × 10 −6 for ϕ γ and ρ γ, respectively.

A bstract This paper presents a measurement of the production cross-section of a Z boson in association with b -jets, 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 35.6 fb − 1 . Inclusive and differential cross-sections are measured for events containing a Z boson decaying into electrons or muons and produced in association with at least one or at least two b -jets with transverse momentum p T > 20 GeV and rapidity |y| < 2 . 5. Predictions from several Monte Carlo generators based on leading-order (LO) or next-to-leading-order (NLO) matrix elements interfaced with a parton-shower simulation and testing different flavour schemes for the choice of initial-state partons are compared with measured cross-sections. The 5-flavour number scheme predictions at NLO accuracy agree better with data than 4-flavour number scheme ones. The 4-flavour number scheme predictions underestimate data in events with at least one b-jet.

A bstract Measurements of four-lepton differential and integrated fiducial cross-sections in events with two same-flavour, opposite-charge electron or muon pairs are presented. The data correspond to 139 fb − 1 of s = 13 TeV proton-proton collisions, collected by the ATLAS detector during Run 2 of the Large Hadron Collider (2015–2018). The final state has contributions from a number of interesting Standard Model processes that dominate in different four-lepton invariant mass regions, including single Z boson production, Higgs boson production and on-shell ZZ production, with a complex mix of interference terms, and possible contributions from physics beyond the Standard Model. The differential cross-sections include the four-lepton invariant mass inclusively, in slices of other kinematic variables, and in different lepton flavour categories. Also measured are dilepton invariant masses, transverse momenta, and angular correlation variables, in four regions of four-lepton invariant mass, each dominated by different processes. The measurements are corrected for detector effects and are compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. The Z → 4 ℓ branching fraction is extracted, giving a value of (4 . 41 ± 0 . 30) × 10 − 6 . Constraints on effective field theory parameters and a model based on a spontaneously broken B − L gauge symmetry are also evaluated. Further reinterpretations can be performed with the provided information.

A bstract We study discovery prospects for a real triplet extension of the Standard Model scalar sector at the Large Hadron Collider (LHC) and a possible future 100 TeV pp collider. We focus on the scenario in which the neutral triplet scalar is stable and contributes to the dark matter relic density. When produced in pp collisions, the charged triplet scalar decays to the neutral component plus a soft pion or soft lepton pair, yielding a disappearing charged track in the detector. We recast current 13 TeV LHC searches for disappearing tracks, and find that the LHC presently excludes a real triplet scalar lighter than 248 (275) GeV, for a mass splitting of 172 (160) MeV with ℒ = 36 fb − 1 . The reach can extend to 497 (520) GeV with the collection of 3000 fb − 1 . We extrapolate the 13 TeV analysis to a prospective 100 TeV pp collider, and find that a ∼ 3 TeV triplet scalar could be discoverable with ℒ = 30 ab − 1 , depending on the degree to which pile up effects are under control. We also investigate the dark matter candidate in our model and corresponding present and prospective constraints from dark matter direct detection. We find that currently XENON1T can exclude a real triplet dark matter lighter than ∼ 3 TeV for a Higgs portal coupling of order one or larger, and the future XENON20T will cover almost the entire dark matter viable parameter space except for vanishingly small portal coupling.

Abstract The decays B+ → J/ψπ+π − K+ are studied using a data set corresponding to an integrated luminosity of 9 fb −1 collected with the LHCb detector in proton-proton collisions between 2011 and 2018. Precise measurements of the ratios of branching fractions with the intermediate ψ2(3823), χc1(3872) and ψ(2S) states are reported. The values are B B + → ψ 2 3823 K + × B ψ 2 3823 → J / ψπ + π − B B + → χ c 1 3872 K + × B χ c 1 3872 → J / ψπ + π − = 3.56 ± 0.67 ± 0.11 × 10 − 2 , B B + → ψ 2 3823 K + × B ψ 2 3823 → J / ψπ + π − B B + → ψ 2 S K + × B ψ 2 S → J / ψπ + π − = 1.31 ± 0.25 ± 0.04 × 10 − 3 , B B + → χ c 1 3872 K + × B χ c 1 3872 → J / ψπ + π − B B + → ψ 2 S K + × B ψ 2 S → J / ψπ + π − = 3.69 ± 0.07 ± 0.06 × 10 − 2 , $$ {\\displaystyle \\begin{array}{c}\\frac{{\\mathcal{B}}_{{\\mathrm{B}}^{+}\\to {\\uppsi}_2(3823){\\mathrm{K}}^{+}}\\times {\\mathcal{B}}_{\\uppsi_2(3823)\\to \\mathrm{J}/{\\uppsi \\uppi}^{+}{\\uppi}^{-}}}{{\\mathcal{B}}_{{\\mathrm{B}}^{+}\\to {\\upchi}_{\\mathrm{c}1}(3872){\\mathrm{K}}^{+}}\\times {\\mathcal{B}}_{\\upchi_{\\mathrm{c}1}(3872)\\to \\mathrm{J}/{\\uppsi \\uppi}^{+}{\\uppi}^{-}}}=\\left(3.56\\pm 0.67\\pm 0.11\\right)\\times {10}^{-2},\\\ {}\\frac{{\\mathcal{B}}_{{\\mathrm{B}}^{+}\\to {\\uppsi}_2(3823){\\mathrm{K}}^{+}}\\times {\\mathcal{B}}_{\\uppsi_2(3823)\\to \\mathrm{J}/{\\uppsi \\uppi}^{+}{\\uppi}^{-}}}{{\\mathcal{B}}_{{\\mathrm{B}}^{+}\\to \\uppsi \\left(2\\mathrm{S}\\right){\\mathrm{K}}^{+}}\\times {\\mathcal{B}}_{\\uppsi \\left(2\\mathrm{S}\\right)\\to \\mathrm{J}/{\\uppsi \\uppi}^{+}{\\uppi}^{-}}}=\\left(1.31\\pm 0.25\\pm 0.04\\right)\\times {10}^{-3},\\\ {}\\frac{{\\mathcal{B}}_{\\mathrm{B}+\\to {\\upchi}_{\\mathrm{c}1}(3872){\\mathrm{K}}^{+}}\\times {\\mathcal{B}}_{\\upchi_{\\mathrm{c}1}(3872)\\to \\mathrm{J}/{\\uppsi \\uppi}^{+}{\\uppi}^{-}}}{{\\mathcal{B}}_{{\\mathrm{B}}^{+}\\to \\uppsi \\left(2\\mathrm{S}\\right){\\mathrm{K}}^{+}}\\times {\\mathcal{B}}_{\\uppsi \\left(2\\mathrm{S}\\right)\\to \\mathrm{J}/{\\uppsi \\uppi}^{+}{\\uppi}^{-}}}=\\left(3.69\\pm 0.07\\pm 0.06\\right)\\times {10}^{-2},\\end{array}} $$ where the first uncertainty is statistical and the second is systematic. The decay of B+ → ψ2(3823)K+ with ψ2(3823) → J/ψπ+π − is observed for the first time with a significance of 5.1 standard deviations. The mass differences between the ψ2(3823), χc1(3872) and ψ(2S) states are measured to be m χ c 1 3872 − m ψ 2 3823 = 47.50 ± 0.53 ± 0.13 MeV / c 2 , m ψ 2 3823 − m ψ 2 2 S = 137.98 ± 0.53 ± 0.14 MeV / c 2 , m χ c 1 3872 − m ψ 2 2 S = 185.49 ± 0.06 ± 0.03 MeV / c 2 , $$ {\\displaystyle \\begin{array}{c}{m}_{\\upchi_{\\mathrm{c}1}(3872)}-{m}_{\\uppsi_2(3823)}=47.50\\pm 0.53\\pm 0.13\\;\\mathrm{MeV}/{c}^2,\\\ {}{m}_{\\uppsi_2(3823)}-{m}_{\\uppsi_2\\left(2\\mathrm{S}\\right)}=137.98\\pm 0.53\\pm 0.14\\;\\mathrm{MeV}/{c}^2,\\\ {}{m}_{\\upchi_{\\mathrm{c}1}(3872)}-{m}_{\\uppsi_2\\left(2\\mathrm{S}\\right)}=185.49\\pm 0.06\\pm 0.03\\;\\mathrm{MeV}/{c}^2,\\end{array}} $$ resulting in the most precise determination of the χc1(3872) mass. The width of the ψ2(3823) state is found to be below 5.2 MeV at 90% confidence level. The Breit-Wigner width of the χc1(3872) state is measured to be Γ χ c 1 3872 BW = 0.96 − 0.18 + 0.19 ± 0.21 MeV $$ {\\Gamma}_{\\upchi_{\\mathrm{c}1}(3872)}^{\\mathrm{BW}}={0.96}_{-0.18}^{+0.19}\\pm 0.21\\;\\mathrm{MeV} $$ which is inconsistent with zero by 5.5 standard deviations.

The inclusive production of the J/ψ and ψ(2S) charmonium states is studied as a function of centrality in p-Pb collisions at a centre-of-mass energy per nucleon pair \\( \\sqrt{s_{\\mathrm{NN}}} \\) = 8.16 TeV at the LHC. The measurement is performed in the dimuon decay channel with the ALICE apparatus in the centre-of-mass rapidity intervals –4.46 < ycms < –2.96 (Pb-going direction) and 2.03 < ycms < 3.53 (p-going direction), down to zero transverse momentum (pT). The J/ψ and ψ(2S) production cross sections are evaluated as a function of the collision centrality, estimated through the energy deposited in the zero degree calorimeter located in the Pb-going direction. The pT-differential J/ψ production cross section is measured at backward and forward rapidity for several centrality classes, together with the corresponding average \\( \\left\\langle {p}_{\\mathrm{T}}\\right\\rangle \\) and \\( \\left\\langle {p}_{\\mathrm{T}}^2\\right\\rangle \\) values. The nuclear effects affecting the production of both charmonium states are studied using the nuclear modification factor. In the p-going direction, a suppression of the production of both charmonium states is observed, which seems to increase from peripheral to central collisions. In the Pb-going direction, however, the centrality dependence is different for the two states: the nuclear modification factor of the J/ψ increases from below unity in peripheral collisions to above unity in central collisions, while for the ψ(2S) it stays below or consistent with unity for all centralities with no significant centrality dependence. The results are compared with measurements in p-Pb collisions at \\( \\sqrt{s_{\\mathrm{NN}}} \\) = 5.02 TeV and no significant dependence on the energy of the collision is observed. Finally, the results are compared with theoretical models implementing various nuclear matter effects.

A bstract The result of a search for the pair production of the lightest supersymmetric partner of the bottom quark b ˜ 1 using 139 fb − 1 of proton-proton data collected at s = 13 TeV by the ATLAS detector is reported. In the supersymmetric scenarios considered both of the bottom-squarks decay into a b -quark and the second-lightest neutralino, b ˜ 1 → b + χ ˜ 2 0 . Each χ ˜ 2 0 is assumed to subsequently decay with 100% branching ratio into a Higgs boson ( h ) like the one in the Standard Model and the lightest neutralino: χ ˜ 2 0 → h + χ ˜ 1 0 . The χ ˜ 1 0 is assumed to be the lightest supersymmetric particle (LSP) and is stable. Two signal mass configurations are targeted: the first has a constant LSP mass of 60 GeV; and the second has a constant mass difference between the χ ˜ 2 0 and χ ˜ 1 0 of 130 GeV. The final states considered contain no charged leptons, three or more b -jets, and large missing transverse momentum. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered. Limits at the 95% confidence level are placed in the supersymmetric models considered, and bottom-squarks with mass up to 1.5 TeV are excluded.

A measurement of event-shape variables in proton-proton collisions at large momentum transfer is presented using data collected at $ \\sqrt{s} $ = 13 TeV with the ATLAS detector at the Large Hadron Collider. Six event-shape variables calculated using hadronic jets are studied in inclusive multijet events using data corresponding to an integrated luminosity of 139 fb-1. Measurements are performed in bins of jet multiplicity and in different ranges of the scalar sum of the transverse momenta of the two leading jets, reaching scales beyond 2 TeV. These measurements are compared with predictions from Monte Carlo event generators containing leading-order or next-to-leading order matrix elements matched to parton showers simulated to leading-logarithm accuracy. At low jet multiplicities, shape discrepancies between the measurements and the Monte Carlo predictions are observed. At high jet multiplicities, the shapes are better described but discrepancies in the normalisation are observed.