| 1. |
- Aad, G., et al.
(author)
-
A search for heavy Higgs bosons decaying into vector bosons in same-sign two-lepton final states in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Journal article (peer-reviewed)abstract
- A search for heavy Higgs bosons produced in association with a vector boson and decaying into a pair of vector bosons is performed in final states with two leptons (electrons or muons) of the same electric charge, missing transverse momentum and jets. A data sample of proton–proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb−1. The observed data are in agreement with Standard Model background expectations. The results are interpreted using higher-dimensional operators in an effective field theory. Upper limits on the production cross-section are calculated at 95% confidence level as a function of the heavy Higgs boson’s mass and coupling strengths to vector bosons. Limits are set in the Higgs boson mass range from 300 to 1500 GeV, and depend on the assumed couplings. The highest excluded mass for a heavy Higgs boson with the coupling combinations explored is 900 GeV. Limits on coupling strengths are also provided.
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| 2. |
- Aad, G., et al.
(author)
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Anomaly detection search for new resonances decaying into a Higgs boson and a generic new particle X in hadronic final states using √s=13 TeV pp collisions with the ATLAS detector
- 2023
-
In: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 108:5
-
Journal article (peer-reviewed)abstract
- A search is presented for a heavy resonance Y decaying into a Standard Model Higgs boson H and a new particle X in a fully hadronic final state. The full Large Hadron Collider run 2 dataset of proton-proton collisions at √s=13 TeV collected by the ATLAS detector from 2015 to 2018 is used and corresponds to an integrated luminosity of 139 fb−1. The search targets the high Y-mass region, where the H and X have a significant Lorentz boost in the laboratory frame. A novel application of anomaly detection is used to define a general signal region, where events are selected solely because of their incompatibility with a learned background-only model. It is constructed using a jet-level tagger for signal-model-independent selection of the boosted X particle, representing the first application of fully unsupervised machine learning to an ATLAS analysis. Two additional signal regions are implemented to target a benchmark X decay into two quarks, covering topologies where the X is reconstructed as either a single large-radius jet or two small-radius jets. The analysis selects Higgs boson decays into , and a dedicated neural-network-based tagger provides sensitivity to the boosted heavy-flavor topology. No significant excess of data over the expected background is observed, and the results are presented as upper limits on the production cross section for signals with mY between 1.5 and 6 TeV and mX between 65 and 3000 GeV.
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| 3. |
- Aad, G., et al.
(author)
-
ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset
- 2023
-
In: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:7
-
Journal article (peer-reviewed)abstract
- The flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of √s=13 TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained.
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| 4. |
- Aad, G., et al.
(author)
-
Calibration of the light-flavour jet mistagging efficiency of the b-tagging algorithms with Z+jets events using 139 fb−1 of ATLAS proton–proton collision data at √s=13 TeV
- 2023
-
In: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:8
-
Journal article (peer-reviewed)abstract
- The identification of b-jets, referred to as b-tagging, is an important part of many physics analyses in the ATLAS experiment at the Large Hadron Collider and an accurate calibration of its performance is essential for high-quality physics results. This publication describes the calibration of the light-flavour jet mistagging efficiency in a data sample of proton–proton collision events at √s=13 TeV corresponding to an integrated luminosity of 139 fb−1. The calibration is performed in a sample of Z bosons produced in association with jets. Due to the low mistagging efficiency for light-flavour jets, a method which uses modified versions of the b-tagging algorithms referred to as flip taggers is used in this work. A fit to the jet-flavour-sensitive secondary-vertex mass is performed to extract a scale factor from data, to correct the light-flavour jet mistagging efficiency in Monte Carlo simulations, while simultaneously correcting the b-jet efficiency. With this procedure, uncertainties coming from the modeling of jets from heavy-flavour hadrons are considerably lower than in previous calibrations of the mistagging scale factors, where they were dominant. The scale factors obtained in this calibration are consistent with unity within uncertainties.
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| 5. |
- Aad, G., et al.
(author)
-
Combined Measurement of the Higgs Boson Mass from the H → γγ and H → ZZ* → 4ℓ Decay Channels with the ATLAS Detector Using √s=7, 8, and 13 TeV pp Collision Data
- 2023
-
In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 131:25
-
Journal article (peer-reviewed)abstract
- A measurement of the mass of the Higgs boson combining the H→ZZ*→4ℓ and H→γγ decay channels is presented. The result is based on 140 fb−1 of proton-proton collision data collected by the ATLAS detector during LHC run 2 at a center-of-mass energy of 13 TeV combined with the run 1 ATLAS mass measurement, performed at center-of-mass energies of 7 and 8 TeV, yielding a Higgs boson mass of 125.11±0.09(stat)±0.06(syst)=125.11±0.11 GeV. This corresponds to a 0.09% precision achieved on this fundamental parameter of the Standard Model of particle physics.
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| 6. |
- Aad, G., et al.
(author)
-
Combined Measurement of the Higgs Boson Mass from the H→γγ and H→ZZ∗→4ℓ Decay Channels with the ATLAS Detector Using √s=7, 8, and 13 TeV pp Collision Data
- 2023
-
In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 131:25
-
Journal article (peer-reviewed)abstract
- A measurement of the mass of the Higgs boson combining the H→ZZ∗→4ℓ and H→γγ decay channels is presented. The result is based on 140 fb−1 of proton-proton collision data collected by the ATLAS detector during LHC run 2 at a center-of-mass energy of 13 TeV combined with the run 1 ATLAS mass measurement, performed at center-of-mass energies of 7 and 8 TeV, yielding a Higgs boson mass of 125.11±0.09(stat)±0.06(syst)=125.11±0.11 GeV. This corresponds to a 0.09% precision achieved on this fundamental parameter of the Standard Model of particle physics.
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| 7. |
- Aad, G., et al.
(author)
-
Constraints on the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at √s=13 TeV
- 2023
-
In: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 843
-
Journal article (peer-reviewed)abstract
- Constraints on the Higgs boson self-coupling are set by combining double-Higgs boson analyses in the b¯bb¯b, b¯bτ +τ − and b¯bγγ decay channels with single-Higgs boson analyses targeting the γγ , Z Z∗, W W ∗, τ +τ − and b¯b decay channels. The data used in these analyses were recorded by the ATLAS detector at the LHC in proton–proton collisions at √s = 13 TeV and correspond to an integrated luminosity of 126–139 fb−1. The combination of the double-Higgs analyses sets an upper limit of μH H < 2.4 at 95% confidence level on the double-Higgs production cross-section normalised to its Standard Model prediction. Combining the single-Higgs and double-Higgs analyses, with the assumption that new physics affects only the Higgs boson self-coupling (λHHH ), values outside the interval −0.4 < κλ = (λHHH /λ ) < 6.3 are excluded at 95% confidence level. The combined single-Higgs and double-Higgs analyses provide results with fewer assumptions, by adding in the fit more coupling modifiers introduced to account for the Higgs boson interactions with the other Standard Model particles. In this relaxed scenario, the constraint becomes −1.4 < κλ < 6.1 at 95% CL
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| 8. |
- Aad, G., et al.
(author)
-
Correlations between flow and transverse momentum in Xe+Xe and Pb+Pb collisions at the LHC with the ATLAS detector : A probe of the heavy-ion initial state and nuclear deformation
- 2023
-
In: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 107:5
-
Journal article (peer-reviewed)abstract
- The correlations between flow harmonics vn for n=2, 3, and 4 and mean transverse momentum [pT] in 129Xe+129Xe and 208Pb+208Pb collisions at √s=5.44 and 5.02 TeV, respectively, are measured using charged particles with the ATLAS detector. The correlations are potentially sensitive to the shape and size of the initial geometry, nuclear deformation, and initial momentum anisotropy. The effects from nonflow and centrality fluctuations are minimized, respectively, via a subevent cumulant method and an event-activity selection based on particle production at very forward rapidity. The vn−[pT] correlations show strong dependencies on centrality, harmonic number n, pT, and pseudorapidity range. Current models qualitatively describe the overall centrality- and system-dependent trends but fail to quantitatively reproduce all features of the data. In central collisions, where models generally show good agreement, the v2−[pT] correlations are sensitive to the triaxiality of the quadruple deformation. Comparison of the model with the Pb+Pb and Xe+Xe data confirms that the 129Xe nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the 129Xe nucleus from high-energy heavy-ion collisions.
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| 9. |
- Aad, G., et al.
(author)
-
Evidence for the charge asymmetry in pp ->†’ t(t)over-bar production at root ˆšs=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479.
-
Journal article (peer-reviewed)abstract
- Inclusive and differential measurements of the top-antitop ( t (t) over bar) charge asymmetry A(C)(t (t) over bar) and the leptonic asymmetry A(C)(l (l) over bar) are presented in proton-proton collisions at root s = 13 TeV recorded by the ATLAS experiment at the CERN Large Hadron Collider. The measurement uses the complete Run 2 dataset, corresponding to an integrated luminosity of 139 fb(-1), combines data in the single-lepton and dilepton channels, and employs reconstruction techniques adapted to both the resolved and boosted topologies. A Bayesian unfolding procedure is performed to correct for detector resolution and acceptance effects. The combined inclusive t (t) over bar charge asymmetry is measured to be A(C)(t (t) over bar) = 0.0068 +/- 0.0015, which differs from zero by 4.7 standard deviations. Differential measurements are performed as a function of the invariant mass, transverse momentum and longitudinal boost of the t (t) over bar system. Both the inclusive and differential measurements are found to be compatible with the Standard Model predictions, at next-to-next-to-leading order in quantum chromodynamics perturbation theory with next-to-leading-order electroweak corrections. The measurements are interpreted in the framework of the Standard Model effective field theory, placing competitive bounds on several Wilson coefficients.
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| 10. |
- Aad, G., et al.
(author)
-
Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ → 4ℓ events with the ATLAS detector at √ˆšs=13 TeV
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :12
-
Journal article (peer-reviewed)abstract
- A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13TeV recorded by the ATLAS detector at the Large Hadron Collider. The ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 +/- 0.60 fb, consistent with the next-to-leadingorder Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.
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| 11. |
- Aad, G., et al.
(author)
-
Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ → 4ℓ events with the ATLAS detector at √s=13 TeV
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2023:12
-
Journal article (peer-reviewed)abstract
- A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 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 ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 ± 0.60 fb, consistent with the next-to-leading-order Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.
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| 12. |
- Aad, G., et al.
(author)
-
Fast b-tagging at the high-level trigger of the ATLAS experiment in LHC Run 3
- 2023
-
In: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 18:11
-
Journal article (peer-reviewed)abstract
- The ATLAS experiment relies on real-time hadronic jet reconstruction and b-tagging to record fully hadronic events containing b-jets. These algorithms require track reconstruction, which is computationally expensive and could overwhelm the high-level-trigger farm, even at the reduced event rate that passes the ATLAS first stage hardware-based trigger. In LHC Run 3, ATLAS has mitigated these computational demands by introducing a fast neural-network-based b-tagger, which acts as a low-precision filter using input from hadronic jets and tracks. It runs after a hardware trigger and before the remaining high-level-trigger reconstruction. This design relies on the negligible cost of neural-network inference as compared to track reconstruction, and the cost reduction from limiting tracking to specific regions of the detector. In the case of Standard Model HH -> b (b) over barb (b) over bar, a key signature relying on b-jet triggers, the filter lowers the input rate to the remaining high-level trigger by a factor of five at the small cost of reducing the overall signal efficiency by roughly 2%.
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| 13. |
- Aad, G., et al.
(author)
-
Fast b-tagging at the high-level trigger of the ATLAS experiment in LHC Run 3
- 2023
-
In: Journal of Instrumentation. - : Institute of Physics. - 1748-0221. ; 18:11
-
Journal article (peer-reviewed)abstract
- The ATLAS experiment relies on real-time hadronic jet reconstruction and b-tagging to record fully hadronic events containing b-jets. These algorithms require track reconstruction, which is computationally expensive and could overwhelm the high-level-trigger farm, even at the reduced event rate that passes the ATLAS first stage hardware-based trigger. In LHC Run 3, ATLAS has mitigated these computational demands by introducing a fast neural-network-based b-tagger, which acts as a low-precision filter using input from hadronic jets and tracks. It runs after a hardware trigger and before the remaining high-level-trigger reconstruction. This design relies on the negligible cost of neural-network inference as compared to track reconstruction, and the cost reduction from limiting tracking to specific regions of the detector. In the case of Standard Model HH → bb̅bb̅, a key signature relying on b-jet triggers, the filter lowers the input rate to the remaining high-level trigger by a factor of five at the small cost of reducing the overall signal efficiency by roughly 2%.
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| 14. |
- Aad, G., et al.
(author)
-
Inclusive and differential cross-sections for dilepton t(t)over-bar production measured in root ˆšs=13 TeV pp collisions with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479.
-
Journal article (peer-reviewed)abstract
- Differential and double-differential distributions of kinematic variables of leptons from decays of top-quark pairs (t (t) over bar) are measured using the full LHC Run 2 data sample collected with the ATLAS detector. The data were collected at a pp collision energy of root s = 13TeV and correspond to an integrated luminosity of 140 fb(-1). The measurements use events containing an oppositely charged e mu pair and b-tagged jets. The results are compared with predictions from several Monte Carlo generators. While no prediction is found to be consistent with all distributions, a better agreement with measurements of the lepton p(T) distributions is obtained by reweighting the t (t) over bar sample so as to reproduce the top-quark p(T) distribution from an NNLO calculation. The inclusive top-quark pair production cross-section is measured as well, both in a fiducial region and in the full phase-space. The total inclusive cross-section is found to be sigma(t (t) over bar) = 829 +/- 1 (stat) +/- 13 (syst) +/- 8 (lumi) +/- 2 (beam) pb, where the uncertainties are due to statistics, systematic effects, the integrated luminosity and the beam energy. This is in excellent agreement with the theoretical expectation.
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| 15. |
- Aad, G., et al.
(author)
-
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
- 2023
-
In: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 108:7
-
Journal article (peer-reviewed)abstract
- The vector-boson production cross section for the Higgs boson decay in the H→WW*→eνμν 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 √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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| 16. |
- Aad, G., et al.
(author)
-
Luminosity determination in pp collisions at √s=13 TeV using the ATLAS detector at the LHC
- 2023
-
In: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:10
-
Journal article (peer-reviewed)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 s=13 TeV. 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 data-taking 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 ± 1.2 fb - 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 ± 3.1 pb - 1 . © 2023, The Author(s).
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| 17. |
- Aad, G., et al.
(author)
-
Measurement of electroweak Z(v (v)over-bar)gamma jj production and limits on anomalous quartic gauge couplings in pp collisions at root s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; :6
-
Journal article (peer-reviewed)abstract
- The electroweak production of Z(v (v) over bar)gamma in association with two jets is studied in a regime with a photon of high transverse momentum above 150 GeV using proton-proton collisions at a centre-of-mass energy of 13TeV at the Large Hadron Collider. The analysis uses a data sample with an integrated luminosity of 139 fb(-1) collected by the ATLAS detector during the 2015-2018 LHC data-taking period. This process is an important probe of the electroweak symmetry breaking mechanism in the Standard Model and is sensitive to quartic gauge boson couplings via vector-boson scattering. The fiducial Z( v (v) over bar)gamma jj cross section for electroweak production is measured to be 0.77(-0.30)(+0.34) fb and is consistent with the Standard Model prediction. Evidence of electroweak Z( v (v) over bar)gamma jj production is found with an observed significance of 3.2 sigma for the background-only hypothesis, compared with an expected significance of 3.7 sigma. The combination of this result with the previously published ATLAS observation of electroweak Z(v (v) over bar)gamma jj production yields an observed (expected) signal significance of 6.3 sigma (6.6 sigma). Limits on anomalous quartic gauge boson couplings are obtained in the framework of effective field theory with dimension-8 operators.
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| 18. |
- Aad, G., et al.
(author)
-
Measurement of the B0s → ΌΌ effective lifetime with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :9
-
Journal article (peer-reviewed)abstract
- This paper reports the first ATLAS measurement of the B-s(0) -> mu mu effective lifetime. The measurement is based on the data collected in 2015-2016, amounting to 26.3 fb(-1) of 13TeV LHC proton-proton collisions. The proper decay-time distribution of 58 +/- 13 background-subtracted signal candidates is fit with simulated signal templates parameterised as a function of the B-s(0) effective lifetime, with statistical uncertainties extracted through a Neyman construction. The resulting effective measurement of the B-s(0) -> mu mu lifetime is 0.99(-0.07)(+0.42) (stat.) +/- 0.17 (syst.) ps and it is found to be consistent with the Standard Model.
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| 19. |
- Aad, G., et al.
(author)
-
Measurement of the polarisation of W bosons produced in top-quark decays using dilepton events at √s=13 TeV with the ATLAS experiment
- 2023
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 843
-
Journal article (peer-reviewed)abstract
- measurement of the polarisation of W bosons produced in top-quark decays is presented, using proton–proton collision data at a centre-of-mass energy of √s=13 TeV. The data were collected by the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 139 fb−1. The measurement is performed selecting events decaying into final states with two charged leptons (electrons or muons) and at least two b-tagged jets. The polarisation is extracted from the differential cross-section distribution of the cosθ* variable, where θ* is the angle between the momentum direction of the charged lepton from the W boson decay and the reversed momentum direction of the b-quark from the top-quark decay, both calculated in the W boson rest frame. Parton-level results, corrected for the detector acceptance and resolution, are presented for the cosθ* angle. The measured fractions of longitudinal, left- and right-handed polarisation states are found to be f0=0.684±0.005(stat.)±0.014(syst.), fL=0.318±0.003(stat.)±0.008(syst.) and fR=−0.002±0.002(stat.)±0.014(syst.), in agreement with the Standard Model prediction.
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| 20. |
- Aad, G., et al.
(author)
-
Measurement of the Sensitivity of Two-Particle Correlations in pp Collisions to the Presence of Hard Scatterings
- 2023
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 131:16
-
Journal article (peer-reviewed)abstract
- A key open question in the study of multiparticle production in high-energy pp collisions is the relationship between the “ridge”—i.e., the observed azimuthal correlations between particles in the underlying event that extend over all rapidities—and hard or semihard scattering processes. In particular, it is not known whether jets or their soft fragments are correlated with particles in the underlying event. To address this question, two-particle correlations are measured in pp collisions at √s=13 TeV using data collected by the ATLAS experiment at the LHC, with an integrated luminosity of 15.8 pb−1, in two different configurations. In the first case, charged particles associated with jets are excluded from the correlation analysis, while in the second case, correlations are measured between particles within jets and charged particles from the underlying event. Second-order flow coefficients, v2, are presented as a function of event multiplicity and transverse momentum. These measurements show that excluding particles associated with jets does not affect the measured correlations. Moreover, particles associated with jets do not exhibit any significant azimuthal correlations with the underlying event, ruling out hard processes contributing to the ridge.
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| 21. |
- Aad, G., et al.
(author)
-
Measurement of the total and differential Higgs boson production cross-sections at √s = 13 TeV with the ATLAS detector by combining the H → ZZ* → 4ℓ and H → γγ decay channels
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:5
-
Journal article (peer-reviewed)abstract
- The total and differential Higgs boson production cross-sections are measured through a combined statistical analysis of the H → ZZ* → 4ℓ and H → γγ 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 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 and decay channels.
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| 22. |
- Aad, G., et al.
(author)
-
Measurement of Zγγ production in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:6
-
Journal article (peer-reviewed)abstract
- Cross-sections for the production of a Z boson in association with two photons are measured in proton–proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 139 fb−1 recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the Z boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated Z(→ℓℓ)γγ cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the Zγγ system. The data are compared with predictions from MC event generators which are accurate to up to next-to-leading order in QCD. The cross-section measurements are used to set limits on the coupling strengths of dimension-8 operators in the framework of an effective field theory.
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| 23. |
- Aad, G., et al.
(author)
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Measurements of multijet event isotropies using optimal transport with the ATLAS detector
- 2023
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In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2023:10
-
Journal article (peer-reviewed)abstract
- A measurement of novel event shapes quantifying the isotropy of collider events is performed in 140 fb−1 of proton-proton collisions with √s = 13 TeV centre-of-mass energy recorded with the ATLAS detector at CERN’s Large Hadron Collider. These event shapes are defined as the Wasserstein distance between collider events and isotropic reference geometries. This distance is evaluated by solving optimal transport problems, using the ‘Energy-Mover’s Distance’. Isotropic references with cylindrical and circular symmetries are studied, to probe the symmetries of interest at hadron colliders. The novel event-shape observables defined in this way are infrared- and collinear-safe, have improved dynamic range and have greater sensitivity to isotropic radiation patterns than other event shapes. The measured event-shape variables are corrected for detector effects, and presented in inclusive bins of jet multiplicity and the scalar sum of the two leading jets’ transverse momenta. The measured distributions are provided as inputs to future Monte Carlo tuning campaigns and other studies probing fundamental properties of QCD and the production of hadronic final states up to the TeV-scale.
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| 24. |
- Aad, G., et al.
(author)
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Measurements of the suppression and correlations of dijets in Pb+Pb collisions at √sNN=5.02 TeV
- 2023
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In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 107:5
-
Journal article (peer-reviewed)abstract
- Studies of the correlations of the two highest transverse momentum (leading) jets in individual Pb+Pb collision events can provide information about the mechanism of jet quenching by the hot and dense matter created in such collisions. In Pb+Pb and pp collisions at √sNN=5.02TeV, measurements of the leading dijet transverse momentum (pT) correlations are presented. Additionally, measurements in Pb+Pb collisions of the dijet pair nuclear modification factors projected along leading and subleading jet pT are made. The measurements are performed using the ATLAS detector at the LHC with 260 pb−1 of pp data collected in 2017 and 2.2 nb−1 of Pb+Pb data collected in 2015 and 2018. An unfolding procedure is applied to the two-dimensional leading and subleading jet pT distributions to account for experimental effects in the measurement of both jets. Results are provided for dijets with leading jet pT greater than 100 GeV. Measurements of the dijet-yield-normalized xJ distributions in Pb+Pb collisions show an increased fraction of imbalanced jets compared to pp collisions; these measurements are in agreement with previous measurements of the same quantity at 2.76 TeV in the overlapping kinematic range. Measurements of the absolutely normalized dijet rate in Pb+Pb and pp collisions are also presented, and show that balanced dijets are significantly more suppressed than imbalanced dijets in Pb+Pb collisions. It is observed in the measurements of the pair nuclear modification factors that the subleading jets are significantly suppressed relative to leading jets with pT between 100 and 316 GeV for all centralities in Pb+Pb collisions
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| 25. |
- Aad, G., et al.
(author)
-
Measurements of Zγ+jets differential cross sections in pp collisions at √s = 13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Journal article (peer-reviewed)abstract
- Differential cross-section measurements of Zγ production in association with hadronic jets are presented, using the full 139 fb−1 dataset of √s = 13 TeV proton–proton collisions collected by the ATLAS detector during Run 2 of the LHC. Distributions are measured using events in which the Z boson decays leptonically and the photon is usually radiated from an initial-state quark. Measurements are made in both one and two observables, including those sensitive to the hard scattering in the event and others which probe additional soft and collinear radiation. Different Standard Model predictions, from both parton-shower Monte Carlo simulation and fixed-order QCD calculations, are compared with the measurements. In general, good agreement is observed between data and predictions from MATRIX and MiNNLOPS, as well as next-to-leading-order predictions from MADGRAPH5_AMC@NLO and SHERPA.
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| 26. |
- Aad, G., et al.
(author)
-
Observation of an Excess of Dicharmonium Events in the Four-Muon Final State with the ATLAS Detector
- 2023
-
In: Physical Review Letters. - : APS. - 0031-9007 .- 1079-7114. ; 131:15
-
Journal article (peer-reviewed)abstract
- A search is made for potential tetraquarks decaying into a pair of charmonium states in the four muon final state using proton-proton collision data at √s = 13 TeV, corresponding to an integrated luminosity of 140 fb−1 recorded by the ATLAS experiment at LHC. Two decay channels, J/ψ + J/ψ → 4μ and J/ψ + ψ(2S) → 4μ, are studied. Backgrounds are estimated based on a hybrid approach involving Monte Carlo simulations and data-driven methods. Statistically significant excesses with respect to backgrounds dominated by the single parton scattering are seen in the di-J/ψ channel consistent with a narrow resonance at 6.9 GeV and a broader structure at lower mass. A statistically significant excess is also seen in the J/ψ + ψ(2S) channel. The fitted masses and decay widths of the structures are reported.
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| 27. |
- Aad, G., et al.
(author)
-
Observation of Single-Top-Quark Production in Association with a Photon Using the ATLAS Detector
- 2023
-
In: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 131:18
-
Journal article (peer-reviewed)abstract
- This Letter reports the observation of single top quarks produced together with a photon, which directly probes the electroweak coupling of the top quark. The analysis uses 139 fb−1 of 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. Requiring a photon with transverse momentum larger than 20 GeV and within the detector acceptance, the fiducial cross section is measured to be 688±23(stat) , to be compared with the standard model prediction of at next-to-leading order in QCD.
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| 28. |
- Aad, G., et al.
(author)
-
Performance of the reconstruction of large impact parameter tracks in the inner detector of ATLAS
- 2023
-
In: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 83:11
-
Journal article (peer-reviewed)abstract
- Searches for long-lived particles (LLPs) are among the most promising avenues for discovering physics beyond the Standard Model at the Large Hadron Collider (LHC). However, displaced signatures are notoriously difficult to identify due to their ability to evade standard object reconstruction strategies. In particular, the ATLAS track reconstruction applies strict pointing requirements which limit sensitivity to charged particles originating far from the primary interaction point. To recover efficiency for LLPs decaying within the tracking detector volume, the ATLAS Collaboration employs a dedicated large-radius tracking (LRT) pass with loosened pointing requirements. During Run 2 of the LHC, the LRT implementation produced many incorrectly reconstructed tracks and was therefore only deployed in small subsets of events. In preparation for LHC Run 3, ATLAS has significantly improved both standard and large-radius track reconstruction performance, allowing for LRT to run in all events. This development greatly expands the potential phase-space of LLP searches and streamlines LLP analysis workflows. This paper will highlight the above achievement and report on the readiness of the ATLAS detector for track-based LLP searches in Run 3.
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| 29. |
- Aad, G., et al.
(author)
-
Production of Υ(nS) mesons in Pb+Pb and pp collisions at 5.02 TeV
- 2023
-
In: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 107:5
-
Journal article (peer-reviewed)abstract
- A measurement of the production of vector bottomonium states, Υ(1S), Υ(2S), and Υ(3S), in Pb+Pb and pp collisions at a center-of-mass energy per nucleon pair of 5.02 TeV is presented. The data correspond to integrated luminosities of 1.38nb−1 of Pb+Pb data collected in 2018, 0.44nb−1 of Pb+Pb data collected in 2015, and 0.26fb−1 of pp data collected in 2017 by the ATLAS detector at the Large Hadron Collider. The measurements are performed in the dimuon decay channel for transverse momentum <30GeV, absolute rapidity |yμμ|<1.5, and Pb+Pb event centrality 0–80%. The production rates of the three bottomonium states in Pb+Pb collisions are compared with those in pp collisions to extract the nuclear modification factors as functions of event centrality, , and |yμμ|. In addition, the suppression of the excited states relative to the ground state is studied. The results are compared with theoretical model calculations.
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| 30. |
- Aad, G., et al.
(author)
-
Search for a light charged Higgs boson in t → H±b decays, with H± → cb, in the lepton plus jets final state in proton-proton collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:9
-
Journal article (peer-reviewed)abstract
- A search for a charged Higgs boson, H±, produced in top-quark decays, t → H±b, is presented. The search targets H± decays into a bottom and a charm quark, H± → cb. The analysis focuses on a selection enriched in top-quark pair production, where one top quark decays into a leptonically decaying W boson and a bottom quark, and the other top quark decays into a charged Higgs boson and a bottom quark. This topology leads to a lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of jets containing b-hadrons, and deploys a neural network classifier that uses the kinematic differences between the signal and the background. The search uses a dataset of proton-proton collisions collected at a centre-of-mass energy √s = 13 TeV between 2015 and 2018 with the ATLAS detector at CERN’s Large Hadron Collider, amounting to an integrated luminosity of 139 fb−1. Observed (expected) 95% confidence-level upper limits between 0.15% (0.09%) and 0.42% (0.25%) are derived for the product of branching fractions for charged Higgs boson masses between 60 and 160 GeV, assuming the SM production of the top-quark pairs.
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| 31. |
- Aad, G., et al.
(author)
-
Search for a new heavy scalar particle decaying into a Higgs boson and a new scalar singlet in final states with one or two light leptons and a pair of τ-leptons with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:10
-
Journal article (peer-reviewed)abstract
- A search for a new heavy scalar particle X decaying into a Standard Model (SM) Higgs boson and a new singlet scalar particle S is presented. The search uses a proton-proton (pp) collision data sample with an integrated luminosity of 140 fb−1 recorded at a centre-of-mass energy of √s= 13 TeV with the ATLAS detector at the Large Hadron Collider. The most sensitive mass parameter space is explored in X mass ranging from 500 to 1500 GeV, with the corresponding S mass in the range 200–500 GeV. The search selects events with two hadronically decaying τ-lepton candidates from H → τ+τ− decays and one or two light leptons (ℓ = e, μ) from S → VV (V = W, Z) decays while the remaining V boson decays hadronically or to neutrinos. A multivariate discriminant based on event kinematics is used to separate the signal from the background. No excess is observed beyond the expected SM background and 95% confidence level upper limits between 72 fb and 542 fb are derived on the cross-section σ(pp → X → SH) assuming the same SM-Higgs boson-like decay branching ratios for the S → VV decay. Upper limits on the visible cross-sections σ(pp → X → SH → WWττ) and σ(pp → X → SH → ZZττ) are also set in the ranges 3–26 fb and 6–33 fb, respectively.
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| 32. |
- Aad, G., et al.
(author)
-
Search for a new scalar resonance in flavour-changing neutral-current top-quark decays t †-> qX (q = u, c), with X ->†’ b(b)over-bar, in proton-proton collisions at root ˆšs=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479.
-
Journal article (peer-reviewed)abstract
- A search for flavour-changing neutral-current decays of a top quark into an up-type quark (either up or charm) and a light scalar particle X decaying into a bottom anti-bottom quark pair is presented. The search focuses on top-quark pair production where one top quark decays to qX, with X -> b (b) over bar, and the other top quark decays according to the Standard Model, with the W boson decaying leptonically. The final state is thus characterised by an isolated electron or muon and at least four jets. Events are categorised according to the multiplicity of jets and jets tagged as originating from b-quarks, and a neural network is used to discriminate between signal and background processes. The data analysed correspond to 139 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13TeV, recorded with the ATLAS detector at the LHC. The 95% confidence-level upper limits between 0.019% and 0.062% are derived for the branching fraction B(t -> uX) and between 0.018% and 0.078% for the branching fraction B(t -> cX), for masses of the scalar particle X between 20 and 160 GeV.
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| 33. |
- Aad, G., et al.
(author)
-
Search for an axion-like particle with forward proton scattering in association with photon pairs at ATLAS
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Journal article (peer-reviewed)abstract
- A search for forward proton scattering in association with light-by-light scattering mediated by an axion-like particle is presented, using the ATLAS Forward Proton spectrometer to detect scattered protons and the central ATLAS detector to detect pairs of outgoing photons. Proton-proton collision data recorded in 2017 at a centre-of-mass energy of √s = 13 TeV were analysed, corresponding to an integrated luminosity of 14.6 fb−1. A total of 441 candidate events were selected. A search was made for a narrow resonance in the diphoton mass distribution, corresponding to an axion-like particle (ALP) with mass in the range 150–1600 GeV. No excess is observed above a smooth background. Upper limits on the production cross section of a narrow resonance are set as a function of the mass, and are interpreted as upper limits on the ALP production coupling constant, assuming 100% decay branching ratio into a photon pair. The inferred upper limit on the coupling constant is in the range 0.04–0.09 TeV−1 at 95% confidence level.
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| 34. |
- Aad, G., et al.
(author)
-
Search for dark matter produced in association with a Higgs boson decaying to tau leptons at √s = 13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2023:9
-
Journal article (peer-reviewed)abstract
- A search for dark matter produced in association with a Higgs boson in final states with two hadronically decaying τ-leptons and missing transverse momentum is presented. The analysis uses 139 fb−1 of proton-proton collision data at √s = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider between 2015 and 2018. No evidence of physics beyond the Standard Model is found. The results are interpreted in terms of a 2HDM+a model featuring two scalar Higgs doublets and a pseudoscalar singlet field. Exclusion limits on the parameters of the model in selected benchmark scenarios are derived at 95% confidence level. Model-independent limits are also set on the visible cross-section for processes beyond the Standard Model producing missing transverse momentum in association with a Higgs boson decaying into τ-leptons.
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| 35. |
- Aad, G., et al.
(author)
-
Search for dark matter produced in association with a single top quark and an energetic W boson in √s=13 TeV pp collisions with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 83:7
-
Journal article (peer-reviewed)abstract
- This paper presents a search for dark matter, χ, using events with a single top quark and an energetic W boson. The analysis is based on proton–proton collision data collected with the ATLAS experiment at √s= 13 TeV during LHC Run 2 (2015–2018), corresponding to an integrated luminosity of 139 fb−1. The search considers final states with zero or one charged lepton (electron or muon), at least one b-jet and large missing transverse momentum. In addition, a result from a previous search considering two-charged-lepton final states is included in the interpretation of the results. The data are found to be in good agreement with the Standard Model predictions and the results are interpreted in terms of 95% confidence-level exclusion limits in the context of a class of dark matter models involving an extended two-Higgs-doublet sector together with a pseudoscalar mediator particle. The search is particularly sensitive to on-shell production of the charged Higgs boson state, H±, arising from the two-Higgs-doublet mixing, and its semi-invisible decays via the mediator particle, a: H±→W±a(→χχ). Signal models with H± masses up to 1.5 TeV and a masses up to 350 GeV are excluded assuming a tan β value of 1. For masses of a of 150 (250) GeV, tan β values up to 2 are excluded for H± masses between 200 (400) GeV and 1.5 TeV. Signals with tan β values between 20 and 30 are excluded for H± masses between 500 and 800 GeV.
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| 36. |
- Aad, G., et al.
(author)
-
Search for dark photons from Higgs boson decays via ZH production with a photon plus missing transverse momentum signature from pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Journal article (peer-reviewed)abstract
- This paper describes a search for dark photons (γd) in proton-proton collisions at √s = 13 TeV at the Large Hadron Collider (LHC). The dark photons are searched for in the decay of Higgs bosons (H → γγd) produced through the ZH production mode. The transverse mass of the system, made of the photon and the missing transverse momentum from the non-interacting γd, presents a distinctive signature as it peaks near the Higgs boson mass. The results presented use the total Run-2 integrated luminosity of 139 fb−1 recorded by the ATLAS detector at the LHC. The dominant reducible background processes are estimated using data-driven techniques. A Boosted Decision Tree technique is adopted to enhance the sensitivity of the search. As no excess is observed with respect to the Standard Model prediction, an observed (expected) upper limit on the branching ratio BR(H → γγd) of 2.28% () is set at 95% CL for massless γd. For massive dark photons up to 40 GeV, the observed (expected) upper limits on BR(H → γγd) at 95% confidence level is found within the [2.19,2.52]% ([2.71,3.11]%) range
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| 37. |
- Aad, G., et al.
(author)
-
Search for Dark Photons in Rare Z Boson Decays with the ATLAS Detector
- 2023
-
In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 131:25
-
Journal article (peer-reviewed)abstract
- A search for events with a dark photon produced in association with a dark Higgs boson via rare decays of the standard model Z boson is presented, using 139 fb−1 of √s=13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider. The dark boson decays into a pair of dark photons, and at least two of the three dark photons must each decay into a pair of electrons or muons, resulting in at least two same-flavor opposite-charge lepton pairs in the final state. The data are found to be consistent with the background prediction, and upper limits are set on the dark photon’s coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, αDϵ2, in the dark photon mass range of [5, 40] GeV except for the Υ mass window [8.8, 11.1] GeV. This search explores new parameter space not previously excluded by other experiments.
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| 38. |
- Aad, G., et al.
(author)
-
Search for direct production of electroweakinos in final states with one lepton, jets and missing transverse momentum in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:12
-
Journal article (peer-reviewed)abstract
- Searches for electroweak production of wino-like chargino pairs, , and of wino-like chargino and next-to-lightest neutralino, , are presented. The models explored assume that the charginos decay into a W boson and the lightest neutralino, . The next-to-lightest neutralinos are degenerate in mass with the chargino and decay to and either a Z or a Higgs boson, or . The searches exploit the presence of a single isolated lepton and missing transverse momentum from the W boson decay products and the lightest neutralinos, and the presence of jets from hadronically decaying Z or W bosons or from the Higgs boson decaying into a pair of b-quarks. The searches use 139 fb−1 of √s = 13 TeV proton-proton collisions data collected by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. No deviations from the Standard Model expectations are found, and 95% confidence level exclusion limits are set. Chargino masses ranging from 260 to 520 GeV are excluded for a massless in chargino pair production models. Degenerate chargino and next-to-lightest neutralino masses ranging from 260 to 420 GeV are excluded for a massless for . For decays through an on-shell Higgs boson and for mass-splitting between and as small as the Higgs boson mass, mass limits are improved by up to 40 GeV in the range of 200–260 GeV and 280–470 GeV compared to previous ATLAS constraints.
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| 39. |
- Aad, G., et al.
(author)
-
Search for direct production of winos and higgsinos in events with two same-charge leptons or three leptons in pp collision data at √s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:11
-
Journal article (peer-reviewed)abstract
- A search for supersymmetry targeting the direct production of winos and higgsinos is conducted in final states with either two leptons (e or μ) with the same electric charge, or three leptons. The analysis uses 139 fb−1 of pp collision data at √s = 13 TeV collected with the ATLAS detector during Run 2 of the Large Hadron Collider. No significant excess over the Standard Model expectation is observed. Simplified and complete models with and without R-parity conservation are considered. In topologies with intermediate states including either Wh or WZ pairs, wino masses up to 525 GeV and 250 GeV are excluded, respectively, for a bino of vanishing mass. Higgsino masses smaller than 440 GeV are excluded in a natural R-parity-violating model with bilinear terms. Upper limits on the production cross section of generic events beyond the Standard Model as low as 40 ab are obtained in signal regions optimised for these models and also for an R-parity-violating scenario with baryon-number-violating higgsino decays into top quarks and jets. The analysis significantly improves sensitivity to supersymmetric models and other processes beyond the Standard Model that may contribute to the considered final states.
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| 40. |
- Aad, G., et al.
(author)
-
Search for displaced photons produced in exotic decays of the Higgs boson using 13 TeV pp collisions with the ATLAS detector
- 2023
-
In: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 108:3
-
Journal article (peer-reviewed)abstract
- A search is performed for delayed and nonpointing photons originating from the displaced decay of a neutral long-lived particle (LLP). The analysis uses the full run 2 dataset of proton-proton collisions delivered by the LHC at a center-of-mass energy of √s=13 TeV between 2015 and 2018 and recorded by the ATLAS detector, corresponding to an integrated luminosity of 139 fb−1. The capabilities of the ATLAS electromagnetic calorimeter are exploited to precisely measure the arrival times and trajectories of photons. The results are interpreted in a scenario where the LLPs are pair produced in exotic decays of the 125 GeV Higgs boson, and each LLP subsequently decays into a photon and a particle that escapes direct detection, giving rise to missing transverse momentum. No significant excess is observed above the expectation due to Standard Model background processes. The results are used to set upper limits on the branching ratio of the exotic decay of the Higgs boson. A model-independent limit is also set on the production of photons with large values of displacement and time delay.
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| 41. |
- Aad, G., et al.
(author)
-
Search for doubly charged Higgs boson production in multi-lepton final states using 139 fb-1 of proton-proton collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 83:7
-
Journal article (peer-reviewed)abstract
- A search for pair production of doubly charged Higgs bosons (H±±), each decaying into a pair of prompt, isolated, and highly energetic leptons with the same electric charge, is presented. The search uses a proton–proton collision data sample at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb−1 recorded by the ATLAS detector during Run 2 of the Large Hadron Collider (LHC). This analysis focuses on same-charge leptonic decays, H±±→ℓ±ℓ′± where ℓ,ℓ′=e,μ,τ, in two-, three-, and four-lepton channels, but only considers final states which include electrons or muons. No evidence of a signal is observed. Corresponding upper limits on the production cross-section of a doubly charged Higgs boson are derived, as a function of its mass m(H±±), at 95% confidence level. Assuming that the branching ratios to each of the possible leptonic final states are equal, , the observed (expected) lower limit on the mass of a doubly charged Higgs boson is 1080 GeV (1065 GeV) within the left-right symmetric type-II seesaw model, which is the strongest limit to date produced by the ATLAS Collaboration. Additionally, this paper provides the first direct test of the Zee–Babu neutrino mass model at the LHC, yielding an observed (expected) lower limit of m(H±±) = 900 GeV (880 GeV).
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| 42. |
- Aad, G., et al.
(author)
-
Search for excited τ-leptons and leptoquarks in the final state with τ-leptons and jets in pp collisions at √s = 13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:6
-
Journal article (peer-reviewed)abstract
- A search is reported for excited τ-leptons and leptoquarks in events with two hadronically decaying τ-leptons and two or more jets. The search uses proton-proton (pp) collision data at √s = 13 TeV recorded by the ATLAS experiment during the Run 2 of the Large Hadron Collider in 2015–2018. The total integrated luminosity is 139 fb−1. The excited τ-lepton is assumed to be produced and to decay via a four-fermion contact interaction into an ordinary τ-lepton and a quark-antiquark pair. The leptoquarks are assumed to be produced in pairs via the strong interaction, and each leptoquark is assumed to couple to a charm or lighter quark and a τ-lepton. No excess over the background prediction is observed. Excited τ-leptons with masses below 2.8 TeV are excluded at 95% CL in scenarios with the contact interaction scale Λ set to 10 TeV. At the extreme limit of model validity where Λ is set equal to the excited τ-lepton mass, excited τ-leptons with masses below 4.6 TeV are excluded. Leptoquarks with masses below 1.3 TeV are excluded at 95% CL if their branching ratio to a charm quark and a τ-lepton equals 1. The analysis does not exploit flavour-tagging in the signal region.
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| 43. |
- Aad, G., et al.
(author)
-
Search for exclusive Higgs and Z boson decays to ωγ and Higgs boson decays to K⁎γ with the ATLAS detector
- 2023
-
In: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 847
-
Journal article (peer-reviewed)abstract
- Searches for the exclusive decays of the Higgs boson to an ? meson and a photon or a ?* meson and a photon can probe flavour-conserving and flavour-violating Higgs boson couplings to light quarks, respectively. Searches for these decays, along with the analogous ? boson decay to an ? meson and a photon, are performed with a ?? collision data sample corresponding to integrated luminosities of up to 134 fb−1 collected at √? = 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. The obtained 95% confidence-level upper limits on the respective branching fractions are (? → ??) < 5.5 × 10−4, (? → ?*?) < 2.2 × 10−4 and (? → ??) < 3.9 × 10−6. The limits for ? → ?? and ? → ?? are 370 times and 140 times the Standard Model expected values, respectively. The result for ? → ?? corresponds to a two-orders-of-magnitude improvement over the limit obtained by the DELPHI experiment at LEP.
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| 44. |
- Aad, G., et al.
(author)
-
Search for flavour-changing neutral tqH interactions with H → γγ in pp collisions at √s=13 TeV using the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2023:12
-
Journal article (peer-reviewed)abstract
- A search for flavour-changing neutral interactions involving the top quark, the Higgs boson and an up-type quark q (q = c, u) is presented. The proton-proton collision data set used, with an integrated luminosity of 139 fb−1, was collected at √s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. Both the decay process t → qH in production and the production process pp → tH, with the Higgs boson decaying into two photons, are investigated. No significant excess is observed and upper limits are set on the t → cH and the t → uH branching ratios of 4.3 × 10−4 and 3.8 × 10−4, respectively, at the 95% confidence level, while the expected limits in the absence of signal are 4.7 × 10−4 and 3.9 × 10−4. Combining this search with ATLAS searches in the H → τ+τ− and H → final states yields observed (expected) upper limits on the t → cH branching ratio of 5.8 × 10−4 (3.0 × 10−4) at the 95% confidence level. The corresponding observed (expected) upper limit on the t → uH branching ratio is 4.0 × 10−4 (2.4 × 10−4).
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| 45. |
- Aad, G., et al.
(author)
-
Search for flavour-changing neutral tqH interactions with H → γγ in pp collisions at √s = 13 TeV using the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2023:12
-
Journal article (peer-reviewed)abstract
- A search for flavour-changing neutral interactions involving the top quark, the Higgs boson and an up-type quark q (q = c, u) is presented. The proton-proton collision data set used, with an integrated luminosity of 139 fb−1, was collected at √s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. Both the decay process t → qH in tt¯ production and the production process pp → tH, with the Higgs boson decaying into two photons, are investigated. No significant excess is observed and upper limits are set on the t → cH and the t → uH branching ratios of 4.3 × 10−4 and 3.8 × 10−4, respectively, at the 95% confidence level, while the expected limits in the absence of signal are 4.7 × 10−4 and 3.9 × 10−4. Combining this search with ATLAS searches in the H → τ+τ− and H → bb¯ final states yields observed (expected) upper limits on the t → cH branching ratio of 5.8 × 10−4 (3.0 × 10−4) at the 95% confidence level. The corresponding observed (expected) upper limit on the t → uH branching ratio is 4.0 × 10−4 (2.4 × 10−4).
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| 46. |
- Aad, G., et al.
(author)
-
Search for heavy Higgs bosons with flavour-violating couplings in multi-lepton plus b-jets final states in pp collisions at 13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2023:12
-
Journal article (peer-reviewed)abstract
- A search for new heavy scalars with flavour-violating decays in final states with multiple leptons and b-tagged jets is presented. The results are interpreted in terms of a general two-Higgs-doublet model involving an additional scalar with couplings to the top-quark and the three up-type quarks (ρtt, ρtc, and ρtu). The targeted signals lead to final states with either a same-sign top-quark pair, three top-quarks, or four top-quarks. The search is based on a data sample of proton-proton collisions at √s = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. Events are categorised depending on the multiplicity of light charged leptons (electrons or muons), total lepton charge, and a deep-neural-network output to enhance the purity of each of the signals. Masses of an additional scalar boson mH between 200 − 630 GeV with couplings ρtt = 0.4, ρtc = 0.2, and ρtu = 0.2 are excluded at 95% confidence level. Additional interpretations are provided in models of R-parity violating supersymmetry, motivated by the recent flavour and (g − 2)μ anomalies.
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| 47. |
- Aad, G., et al.
(author)
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Search for heavy Higgs bosons with flavour-violating couplings in multi-lepton plus b-jets final states in pp collisions at 13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:12
-
Journal article (peer-reviewed)abstract
- A search for new heavy scalars with flavour-violating decays in final states with multiple leptons and b-tagged jets is presented. The results are interpreted in terms of a general two-Higgs-doublet model involving an additional scalar with couplings to the top-quark and the three up-type quarks (). The targeted signals lead to final states with either a same-sign top-quark pair, three top-quarks, or four top-quarks. The search is based on a data sample of proton-proton collisions at √s = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. Events are categorised depending on the multiplicity of light charged leptons (electrons or muons), total lepton charge, and a deep-neural-network output to enhance the purity of each of the signals. Masses of an additional scalar boson mH between 200 − 630 GeV with couplings , , and are excluded at 95% confidence level. Additional interpretations are provided in models of R-parity violating supersymmetry, motivated by the recent flavour and (g − 2)μ anomalies.
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| 48. |
- Aad, G., et al.
(author)
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Search for heavy long-lived multi-charged particles in the full LHC Run 2 pp collision data at √s=13 TeV using the ATLAS detector
- 2023
-
In: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 847
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Journal article (peer-reviewed)abstract
- A search for heavy long-lived multi-charged particles is performed using the ATLAS detector at the LHC. Data collected in 2015-2018 at √s = 13 TeV from pp collisions corresponding to an integrated luminosity of 139 fb−1 are examined. Particles producing anomalously high ionization, consistent with long-lived spin-½ massive particles with electric charges from |q| = 2e to |q| = 7e are searched for. No statistically significant evidence of such particles is observed, and 95% confidence level cross-section upper limits are calculated and interpreted as the lower mass limits for a Drell-Yan plus photon-fusion production mode. The least stringent limit, 1060 GeV, is obtained for |q| = 2e particles, and the most stringent one, 1600 GeV, is for |q| = 6e particles.
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| 49. |
- Aad, G., et al.
(author)
-
Search for heavy Majorana or Dirac neutrinos and right-handed W gauge bosons in final states with charged leptons and jets in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 83:12
-
Journal article (peer-reviewed)abstract
- A search for heavy right-handed Majorana or Dirac neutrinos NR and heavy right-handed gauge bosons WR is performed in events with energetic electrons or muons, with the same or opposite electric charge, and energetic jets. The search is carried out separately for topologies of clearly separated final-state products (“resolved” channel) and topologies with boosted final states with hadronic and/or leptonic products partially overlapping and reconstructed as a large-radius jet (“boosted” channel). The events are selected from pp collision data at the LHC with an integrated luminosity of 139 fb−1 collected by the ATLAS detector at √s=13 TeV. No significant deviations from the Standard Model predictions are observed. The results are interpreted within the theoretical framework of a left-right symmetric model, and lower limits are set on masses in the heavy right-handed WR boson and NR plane. The excluded region extends to about m(WR)=6.4 TeV for both Majorana and Dirac NR neutrinos at m(NR)<1 TeV. NR with masses of less than 3.5 (3.6) TeV are excluded in the electron (muon) channel at m(WR)=4.8 TeV for the Majorana neutrinos, and limits of m(NR) up to 3.6 TeV for m(WR)=5.2 (5.0) TeV in the electron (muon) channel are set for the Dirac neutrinos. These constitute the most stringent exclusion limits to date for the model considered.
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| 50. |
- Aad, G., et al.
(author)
-
Search for leptoquarks decaying into the bτ final state in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:10
-
Journal article (peer-reviewed)abstract
- A search for leptoquarks decaying into the bτ final state is performed using Run 2 proton-proton collision data from the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1 at √s = 13 TeV recorded by the ATLAS detector. The benchmark models considered in this search are vector leptoquarks with electric charge of 2/3e and scalar leptoquarks with an electric charge of 4/3e. No significant excess above the Standard Model prediction is observed, and 95% confidence level upper limits are set on the cross-section times branching fraction of leptoquarks decaying into bτ. For the vector leptoquark production two models are considered: the Yang-Mills and Minimal coupling models. In the Yang-Mills (Minimal coupling) scenario, vector leptoquarks with a mass below 1.58 (1.35) TeV are excluded for a gauge coupling of 1.0 and below 2.05 (1.99) TeV for a gauge coupling of 2.5. In the case of scalar leptoquarks, masses below 1.28 (1.53) TeV are excluded for a Yukawa coupling of 1.0 (2.5). Finally, an interpretation of the results with minimal model dependence is performed for each of the signal region categories, and limits on the visible cross-section for beyond the Standard Model processes are provided.
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