| 1. |
- Aad, G., et al.
(författare)
-
A search for top-squark pair production, in final states containing a top quark, a charm quark and missing transverse momentum, using the 139 fb−1 of pp collision data collected by the ATLAS detector
- 2024
-
Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2024:7
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a search for top-squark pair production in final states with a top quark, a charm quark and missing transverse momentum. The data were collected with the ATLAS detector during LHC Run 2 and correspond to an integrated luminosity of 139 fb−1 of proton-proton collisions at a centre-of-mass energy of s = 13 TeV. The analysis is motivated by an extended Minimal Supersymmetric Standard Model featuring a non-minimal flavour violation in the second- and third-generation squark sector. The top squark in this model has two possible decay modes, either t~1→cχ~10 or t~1→tχ~10, where the χ~10 is undetected. The analysis is optimised assuming that both of the decay modes are equally probable, leading to the most likely final state of tc+ETmiss. Good agreement is found between the Standard Model expectation and the data in the search regions. Exclusion limits at 95% CL are obtained in the mt~1 vs. mχ~10 plane and, in addition, limits on the branching ratio of the t~1→tχ~10 decay as a function of m(t~1) are also produced. Top-squark masses of up to 800 GeV are excluded for scenarios with light neutralinos, and top-squark masses up to 600 GeV are excluded in scenarios where the neutralino and the top squark are almost mass degenerate. © The Author(s) 2024.
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| 2. |
- Aad, G, et al.
(författare)
-
Azimuthal Angle Correlations of Muons Produced via Heavy-Flavor Decays in 5.02 TeV Pb+Pb and pp Collisions with the ATLAS Detector
- 2024
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Ingår i: Physical Review Letters. - 0031-9007. ; 132:20
-
Tidskriftsartikel (refereegranskat)abstract
- Angular correlations between heavy quarks provide a unique probe of the quark-gluon plasma created in ultrarelativistic heavy-ion collisions. Results are presented of a measurement of the azimuthal angle correlations between muons originating from semileptonic decays of heavy quarks produced in 5.02 TeV Formula Presented and Formula Presented collisions at the LHC. The muons are measured with transverse momenta and pseudorapidities satisfying Formula Presented and Formula Presented, respectively. The distributions of azimuthal angle separation Formula Presented for muon pairs having pseudorapidity separation Formula Presented, are measured in different Formula Presented centrality intervals and compared to the same distribution measured in Formula Presented collisions at the same center-of-mass energy. Results are presented separately for muon pairs with opposite-sign charges, same-sign charges, and all pairs. A clear peak is observed in all Formula Presented distributions at Formula Presented, consistent with the parent heavy-quark pairs being produced via hard-scattering processes. The widths of that peak, characterized using Cauchy-Lorentz fits to the Formula Presented distributions, are found to not vary significantly as a function of Formula Presented collision centrality and are similar for Formula Presented and Formula Presented collisions. This observation will provide important constraints on theoretical descriptions of heavy-quark interactions with the quark-gluon plasma. © 2024 CERN, for the ATLAS Collaboration.
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| 3. |
- Aad, G., et al.
(författare)
-
Combination of searches for pair-produced leptoquarks at s=13 TeV with the ATLAS detector
- 2024
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 854
-
Tidskriftsartikel (refereegranskat)abstract
- A statistical combination of various searches for pair-produced leptoquarks is presented, using the full LHC Run 2 (2015–2018) data set of 139 fb−1 collected with the ATLAS detector from proton–proton collisions at a centre-of-mass energy of s=13 TeV. All possible decays of the leptoquarks into quarks of the third generation and charged or neutral leptons of any generation are investigated. Since no significant deviations from the Standard Model expectation are observed in any of the individual analyses, combined exclusion limits are set on the production cross-sections for scalar and vector leptoquarks. The resulting lower bounds on leptoquark masses exceed those from the individual analyses by up to 100 GeV, depending on the signal hypothesis. © 2024 The Author(s)
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| 4. |
- Aad, G., et al.
(författare)
-
Combination of Searches for Resonant Higgs Boson Pair Production Using pp Collisions at sqrt[s]=13 TeV with the ATLAS Detector
- 2024
-
Ingår i: Physical Review Letters. - 1079-7114. ; 132:23
-
Tidskriftsartikel (refereegranskat)abstract
- A combination of searches for a new resonance decaying into a Higgs boson pair is presented, using up to 139 fb^{-1} of pp collision data at sqrt[s]=13 TeV recorded with the ATLAS detector at the LHC. The combination includes searches performed in three decay channels: bb[over ¯]bb[over ¯], bb[over ¯]τ^{+}τ^{-}, and bb[over ¯]γγ. No excess above the expected Standard Model background is observed and upper limits are set at the 95% confidence level on the production cross section of Higgs boson pairs originating from the decay of a narrow scalar resonance with mass in the range 251 GeV-5 TeV. The observed (expected) limits are in the range 0.96-600 fb (1.2-390 fb). The limits are interpreted in the type-I two-Higgs-doublet model and the minimal supersymmetric standard model, and constrain parameter space not previously excluded by other searches.
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| 5. |
- Aad, G., et al.
(författare)
-
Inclusive and differential cross-section measurements of tt¯Z production in pp collisions at s = 13 TeV with the ATLAS detector, including EFT and spin-correlation interpretations
- 2024
-
Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2024:7
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of both the inclusive and differential production cross sections of a top-quark-top-antiquark pair in association with a Z boson (tt¯Z) are presented. Final states with two, three or four isolated leptons (electrons or muons) are targeted. The measurements use the data recorded by the ATLAS detector in pp collisions at s = 13 TeV at the Large Hadron Collider during the years 2015–2018, corresponding to an integrated luminosity of 140 fb−1. The inclusive cross section is measured to be σtt¯Z = 0.86 ± 0.04 (stat.) ± 0.04 (syst.) pb and found to be in agreement with the most advanced Standard Model predictions. The differential measurements are presented as a function of a number of observables that probe the kinematics of the tt¯Z system. Both the absolute and normalised differential cross-section measurements are performed at particle level and parton level for specific fiducial volumes, and are compared with NLO+NNLL theoretical predictions. The results are interpreted in the framework of Standard Model effective field theory and used to set limits on a large number of dimension-6 operators involving the top quark. The first measurement of spin correlations in tt¯Z events is presented: the results are in agreement with the Standard Model expectations, and the null hypothesis of no spin correlations is disfavoured with a significance of 1.8 standard deviations. © The Author(s) 2024.
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| 6. |
- Aad, G., et al.
(författare)
-
Luminosity determination in pp collisions at √s=13 TeV using the ATLAS detector at the LHC
- 2023
-
Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:10
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Aad, G., et al.
(författare)
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Measurement of the Centrality Dependence of the Dijet Yield in Formula Presented Collisions at Formula Presented with the ATLAS Detector
- 2024
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 132:10
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Tidskriftsartikel (refereegranskat)abstract
- ATLAS measured the centrality dependence of the dijet yield using Formula Presented of Formula Presented data collected at Formula Presented in 2016. The event centrality, which reflects the Formula Presented impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, Formula Presented, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The Formula Presented shows a scaling with the Bjorken Formula Presented of the parton originating from the proton, Formula Presented, while no such trend is observed as a function of Formula Presented. This analysis provides unique input to understanding the role of small proton spatial configurations in Formula Presented collisions by covering parton momentum fractions from the valence region down to Formula Presented and Formula Presented. © 2024 CERN, for the ATLAS Collaboration.
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| 8. |
- Aad, G., et al.
(författare)
-
Measurement of the VH,H → ττ process with the ATLAS detector at 13 TeV
- 2024
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 855
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the Standard Model Higgs boson produced in association with a W or Z boson and decaying into a pair of τ-leptons is presented. This search is based on proton-proton collision data collected at s=13 TeV by the ATLAS experiment at the LHC corresponding to an integrated luminosity of 140 fb−1. For the Higgs boson candidate, only final states with at least one τ-lepton decaying hadronically (τ→hadrons+ντ) are considered. For the vector bosons, only leptonic decay channels are considered: Z→ℓℓ and W→ℓνℓ, with ℓ=e,μ. An excess of events over the expected background is found with an observed (expected) significance of 4.2 (3.6) standard deviations, providing evidence of the Higgs boson produced in association with a vector boson and decaying into a pair of τ-leptons. The ratio of the measured cross-section to the Standard Model prediction is μVHττ=1.28−0.29+0.30(stat.)−0.21+0.25(syst.). This result represents the most accurate measurement of the VH(ττ) process achieved to date. © 2024 The Author(s)
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| 9. |
- Aad, G., et al.
(författare)
-
Measurement of the Z boson invisible width at s=13 TeV with the ATLAS detector
- 2024
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 854
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the invisible width of the Z boson using events with jets and missing transverse momentum is presented using 37 fb−1 of 13 TeV proton–proton data collected by the ATLAS detector in 2015 and 2016. The ratio of Z→inv to Z→ℓℓ events, where inv refers to non-detected particles and ℓ is either an electron or a muon, is measured and corrected for detector effects. Events with at least one energetic central jet with pT≥110 GeV are selected for both the Z→inv and Z→ℓℓ final states to obtain a similar phase space in the ratio. The invisible width is measured to be 506±2(stat.)±12(syst.) MeV and is the single most precise recoil-based measurement. The result is in agreement with the most precise determination from LEP and the Standard Model prediction based on three neutrino generations. © 2024 The Author(s)
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| 10. |
- Aad, G., et al.
(författare)
-
Measurement of ZZ production cross-sections in the four-lepton final state in pp collisions at s=13.6TeV with the ATLAS experiment
- 2024
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 855
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports cross-section measurements of ZZ production in pp collisions at s=13.6TeV at the Large Hadron Collider. The data were collected by the ATLAS detector in 2022, and correspond to an integrated luminosity of 29 fb−1. Events in the ZZ→4ℓ (ℓ=e, μ) final states are selected and used to measure the inclusive and differential cross-sections in a fiducial region defined close to the analysis selections. The inclusive cross-section is further extrapolated to the total phase space with a requirement of 66
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| 11. |
- Aad, G., et al.
(författare)
-
Observation of electroweak production of W+W− in association with jets in proton-proton collisions at s = 13 TeV with the ATLAS detector
- 2024
-
Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2024:7
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the production of W bosons with opposite electric charges in association with two jets is presented based on 140 fb−1 of data collected by the ATLAS detector in proton-proton collisions at s = 13 TeV. The analysis is sensitive to the scattering of W bosons, which is of particular interest in the ATLAS physics programme as it can be used to probe the electroweak symmetry breaking mechanism of the Standard Model. This signal is observed with a significance of 7.1 standard deviations above the background expectation, while 6.2 standard deviations were expected. The measured cross-section is determined in a signal-enriched fiducial volume and is found to be 2.7 ± 0.5 fb, which is consistent with the theoretical prediction of 2.20−0.13+0.14 fb. © The Author(s) 2024.
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| 12. |
- Aad, G, et al.
(författare)
-
Search for charged-lepton-flavor violating Formula Presented interactions in top-quark production and decay in Formula Presented collisions at Formula Presented with the ATLAS detector at the LHC
- 2024
-
Ingår i: Physical Review D. - : American Physical Society (APS). - 2470-0010 .- 2470-0029. ; 110:1
-
Tidskriftsartikel (refereegranskat)abstract
- A search for charged-lepton-flavor violating Formula Presented (Formula Presented, Formula Presented) interactions is presented, considering both top-quark production and decay. The data analyzed correspond to Formula Presented of proton-proton collisions at a center-of-mass energy of Formula Presented recorded with the ATLAS detector at the Large Hadron Collider. The analysis targets events containing two muons with the same electric charge, a hadronically decaying Formula Presented-lepton and at least one jet, with exactly one Formula Presented-tagged jet, produced by a Formula Presented interaction. Agreement with the Standard Model expectation within 1.6 standard deviations is observed, and limits are set at the 95% confidence level (CL) on the charged-lepton-flavor violation branching ratio of Formula Presented. An effective field theory interpretation is performed yielding 95% CL limits on Wilson coefficients, dependent on the flavor of the associated light quark and the Lorentz structure of the coupling. These range from Formula Presented for Formula Presented to Formula Presented for Formula Presented. An additional interpretation is performed for scalar leptoquark production inducing charged-lepton-flavor violation, with fixed intergenerational couplings. Upper limits on leptoquark coupling strengths are set at the 95% CL, ranging from Formula Presented to Formula Presented for leptoquark masses between 0.5 and 2.0 TeV. © 2024 CERN, for the ATLAS Collaboration.
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| 13. |
- Aad, G., et al.
(författare)
-
Search for flavour-changing neutral-current couplings between the top quark and the Higgs boson in multi-lepton final states in 13 TeV pp collisions with the ATLAS detector
- 2024
-
Ingår i: European Physical Journal C. - 1434-6044. ; 84:7
-
Tidskriftsartikel (refereegranskat)abstract
- A search is presented for flavour-changing neutral-current interactions involving the top quark, the Higgs boson and an up-type quark (q=u,c) with the ATLAS detector at the Large Hadron Collider. The analysis considers leptonic decays of the top quark along with Higgs boson decays into two W bosons, two Z bosons or a τ+τ- pair. It focuses on final states containing either two leptons (electrons or muons) of the same charge or three leptons. The considered processes are tt¯ and Ht production. For the tt¯ production, one top quark decays via t→Hq. The proton–proton collision data set analysed amounts to (140fb-1) at (s=13TeV). No significant excess beyond Standard Model expectations is observed and upper limits are set on the t→Hq branching ratios at 95 % confidence level, amounting to observed (expected) limits of B(t→Hu)
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| 14. |
- Aad, G., et al.
(författare)
-
Search for Nearly Mass-Degenerate Higgsinos Using Low-Momentum Mildly Displaced Tracks in pp Collisions at sqrt[s]=13 TeV with the ATLAS Detector
- 2024
-
Ingår i: Physical Review Letters. - : American Physical Society (APS). - 1079-7114 .- 0031-9007. ; 132:22
-
Tidskriftsartikel (refereegranskat)abstract
- Higgsinos with masses near the electroweak scale can solve the hierarchy problem and provide a dark matter candidate, while detecting them at the LHC remains challenging if their mass splitting is O(1 GeV). This Letter presents a novel search for nearly mass-degenerate Higgsinos in events with an energetic jet, missing transverse momentum, and a low-momentum track with a significant transverse impact parameter using 140 fb^{-1} of proton-proton collision data at sqrt[s]=13 TeV collected by the ATLAS experiment. For the first time since LEP, a range of mass splittings between the lightest charged and neutral Higgsinos from 0.3 to 0.9 GeV is excluded at 95% confidence level, with a maximum reach of approximately 170 GeV in the Higgsino mass.
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| 15. |
- Aad, G., et al.
(författare)
-
Search for non-resonant Higgs boson pair production in the 2b+2ℓ+ETmiss final state in pp collisions at s = 13 TeV with the ATLAS detector
- 2024
-
Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2024:2
-
Tidskriftsartikel (refereegranskat)abstract
- A search for non-resonant Higgs boson pair (HH) production is presented, in which one of the Higgs bosons decays to a b-quark pair (bb¯) and the other decays to WW*, ZZ*, or τ+τ−, with in each case a final state with ℓ+ℓ−+ neutrinos (ℓ = e, μ). The analysis targets separately the gluon-gluon fusion and vector boson fusion production modes. Data recorded by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb−1, are used in this analysis. Events are selected to have exactly two b-tagged jets and two leptons with opposite electric charge and missing transverse momentum in the final state. These events are classified using multivariate analysis algorithms to separate the HH events from other Standard Model processes. No evidence of the signal is found. The observed (expected) upper limit on the cross-section for non-resonant Higgs boson pair production is determined to be 9.7 (16.2) times the Standard Model prediction at 95% confidence level. The Higgs boson self-interaction coupling parameter κλ and the quadrilinear coupling parameter κ2V are each separately constrained by this analysis to be within the ranges [−6.2, 13.3] and [−0.17, 2.4], respectively, at 95% confidence level, when all other parameters are fixed. © The Author(s) 2024.
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| 16. |
- Aad, G, et al.
(författare)
-
Search for pair production of higgsinos in events with two Higgs bosons and missing transverse momentum in Formula Presented Formula Presented collisions at the ATLAS experiment
- 2024
-
Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 109:11
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a search for pair production of higgsinos, the supersymmetric partners of the Higgs bosons, in scenarios with gauge-mediated supersymmetry breaking. Each higgsino is assumed to decay into a Higgs boson and a nearly massless gravitino. The search targets events where each Higgs boson decays into Formula Presented, leading to a reconstructed final state with at least three energetic Formula Presented-jets and missing transverse momentum. Two complementary analysis channels are used, with each channel specifically targeting either low or high values of the higgsino mass. The low-mass (high-mass) channel exploits Formula Presented of Formula Presented data collected by the ATLAS detector during Run 2 of the Large Hadron Collider. No significant excess above the Standard Model prediction is found. At 95% confidence level, masses between 130 GeV and 940 GeV are excluded for higgsinos decaying exclusively into Higgs bosons and gravitinos. Exclusion limits as a function of the higgsino decay branching ratio to a Higgs boson are also reported. © 2024 CERN, for the ATLAS Collaboration.
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| 17. |
- Aad, G., et al.
(författare)
-
Search for pair-production of vector-like quarks in lepton+jets final states containing at least one b-tagged jet using the Run 2 data from the ATLAS experiment
- 2024
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 854
-
Tidskriftsartikel (refereegranskat)abstract
- A search is presented for the pair-production of heavy vector-like quarks in the lepton+jets final state using 140 fb−1 of proton–proton collisions at s=13 TeV collected with the ATLAS detector. The search is optimised for vector-like top-quarks (T) that decay into a W boson and a b-quark, with one W boson decaying leptonically and the other hadronically. Other vector-like quark flavours and decay modes are also considered. Events are selected with one high transverse-momentum electron or muon, large missing transverse momentum, a large-radius jet identified as a W boson, and multiple small-radius jets, at least one of which is b-tagged. Vector-like T-quarks with 100% branching ratio to Wb are excluded at 95% CL for masses below 1700 GeV. These limits are also applied to vector-like Y-quarks, which decay exclusively into a W boson and a b-quark. Isospin singlets with B(T→Wb:Ht:Zt)=1/2:1/4:1/4 are excluded for masses below 1360 GeV. © 2024 The Author(s)
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| 18. |
- Aad, G., et al.
(författare)
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Search for short- and long-lived axion-like particles in H→aa→4γ decays with the ATLAS experiment at the LHC
- 2024
-
Ingår i: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 84:7
-
Tidskriftsartikel (refereegranskat)abstract
- Presented is the search for anomalous Higgs boson decays into two axion-like particles (ALPs) using the full Run 2 data set of 140fb-1 of proton-proton collisions at a centre-of-mass energy of 13TeV recorded by the ATLAS experiment. The ALPs are assumed to decay into two photons, providing sensitivity to recently proposed models that could explain the (g-2)μ discrepancy. This analysis covers an ALP mass range from 100 to 62GeV and ALP-photon couplings in the range 10-7TeV-1
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| 19. |
- Aad, G, et al.
(författare)
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Search for singly produced vectorlike top partners in multilepton final states with Formula Presented of Formula Presented collision data at Formula Presented with the ATLAS detector
- 2024
-
Ingår i: Physical Review D. - : American Physical Society (APS). - 2470-0010 .- 2470-0029. ; 109:11
-
Tidskriftsartikel (refereegranskat)abstract
- A search for the single production of a vectorlike top partner (Formula Presented) with mass greater than 1 TeV decaying into a Formula Presented boson and a top quark is presented, using the full Run 2 dataset corresponding to Formula Presented of Formula Presented collisions at Formula Presented, collected in 2015-2018 with the ATLAS detector at the Large Hadron Collider. The targeted final state is characterized by the presence of a pair of electrons or muons with opposite-sign charges which form a Formula Presented-boson candidate, as well as by the presence of Formula Presented-tagged jets and forward jets. Events with exactly two or at least three leptons are categorized into two independently optimized analysis channels. No significant excess above the background expectation is observed and the results from the two channels are statistically combined to set exclusion limits at 95% confidence level on the masses and couplings of Formula Presented. The results are interpreted in several benchmark scenarios to set limits on the mass and universal coupling strength (Formula Presented) of the vectorlike quark. For singlet Formula Presented quarks, Formula Presented values between 0.22 and 0.64 are excluded for masses between 1000 and 1975 GeV. For Formula Presented quarks in the doublet scenario, where the production cross section is much lower, Formula Presented values between 0.54 and 0.88 are excluded for masses between 1000 and 1425 GeV.
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| 20. |
- Aad, G., et al.
(författare)
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Search for top-philic heavy resonances in pp collisions at s=13 TeV with the ATLAS detector
- 2024
-
Ingår i: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 84:2
-
Tidskriftsartikel (refereegranskat)abstract
- A search for the associated production of a heavy resonance with a top-quark or a top-antitop-quark pair, and decaying into a tt¯ pair is presented. The search uses the data recorded by the ATLAS detector in pp collisions at s=13 TeV at the Large Hadron Collider during the years 2015–2018, corresponding to an integrated luminosity of 139 fb-1. Events containing exactly one electron or muon are selected. The two hadronically decaying top quarks from the resonance decay are reconstructed using jets clustered with a large radius parameter of R=1. The invariant mass spectrum of the two top quark candidates is used to search for a resonance signal in the range of 1.0 TeV to 3.2 TeV. The presence of a signal is examined using an approach with minimal model dependence followed by a model-dependent interpretation. No significant excess is observed over the background expectation. Upper limits on the production cross section times branching ratio at 95% confidence level are provided for a heavy Z′ boson based on a simplified model, for Z′ mass between 1.0 TeV and 3.0 TeV. The observed (expected) limits range from 21 (14) fb to 119 (86) fb depending on the choice of model parameters. © The Author(s) 2024.
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| 21. |
- Aad, G., et al.
(författare)
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Searches for exclusive Higgs boson decays into D⁎γ and Z boson decays into D0γ and Ks0γ in pp collisions at s=13TeV with the ATLAS detector
- 2024
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 855
-
Tidskriftsartikel (refereegranskat)abstract
- Searches for exclusive decays of the Higgs boson into D⁎γ and of the Z boson into D0γ and Ks0γ can probe flavour-violating Higgs boson and Z boson couplings to light quarks. Searches for these decays are performed with a pp collision data sample corresponding to an integrated luminosity of 136.3 fb−1 collected at s=13TeV between 2016–2018 with the ATLAS detector at the CERN Large Hadron Collider. In the D⁎γ and D0γ channels, the observed (expected) 95% confidence-level upper limits on the respective branching fractions are B(H→D⁎γ)
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| 22. |
- Aad, G., et al.
(författare)
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Software Performance of the ATLAS Track Reconstruction for LHC Run 3
- 2024
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Ingår i: Computing and Software for Big Science. - : Springer Nature. - 2510-2044. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Charged particle reconstruction in the presence of many simultaneous proton–proton (pp) collisions in the LHC is a challenging task for the ATLAS experiment’s reconstruction software due to the combinatorial complexity. This paper describes the major changes made to adapt the software to reconstruct high-activity collisions with an average of 50 or more simultaneous pp interactions per bunch crossing (pile-up) promptly using the available computing resources. The performance of the key components of the track reconstruction chain and its dependence on pile-up are evaluated, and the improvement achieved compared to the previous software version is quantified. For events with an average of 60pp collisions per bunch crossing, the updated track reconstruction is twice as fast as the previous version, without significant reduction in reconstruction efficiency and while reducing the rate of combinatorial fake tracks by more than a factor two. © The Author(s) 2024.
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| 23. |
- Aad, G., et al.
(författare)
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Statistical Combination of ATLAS Run 2 Searches for Charginos and Neutralinos at the LHC
- 2024
-
Ingår i: Physical Review Letters. - : American Physical Society (APS). - 1079-7114 .- 0031-9007. ; 133:3
-
Tidskriftsartikel (refereegranskat)abstract
- Statistical combinations of searches for charginos and neutralinos using various decay channels are performed using 139 fb^{-1} of pp collision data at sqrt[s]=13 TeV with the ATLAS detector at the Large Hadron Collider. Searches targeting pure-wino chargino pair production, pure-wino chargino-neutralino production, or Higgsino production decaying via standard model W, Z, or h bosons are combined to extend the mass reach to the produced supersymmetric particles by 30-100 GeV. The depth of the sensitivity of the original searches is also improved by the combinations, lowering the 95% C.L. cross-section upper limits by 15%-40%.
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| 24. |
- Aad, G., et al.
(författare)
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Study of Z→llγ decays at s = 8 TeV with the ATLAS detector
- 2024
-
Ingår i: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 84:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of Z→llγ decays with the ATLAS detector at the Large Hadron Collider. The analysis uses a proton–proton data sample corresponding to an integrated luminosity of 20.2 fb-1 collected at a centre-of-mass energy s = 8 TeV. Integrated fiducial cross-sections together with normalised differential fiducial cross-sections, sensitive to the kinematics of final-state QED radiation, are obtained. The results are found to be in agreement with state-of-the-art predictions for final-state QED radiation. First measurements of Z→llγγ decays are also reported. © The Author(s) 2024.
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| 25. |
- Aad, G, et al.
(författare)
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The ATLAS experiment at the CERN Large Hadron Collider: a description of the detector configuration for Run 3
- 2024
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 19:5
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Tidskriftsartikel (refereegranskat)abstract
- The ATLAS detector is installed in its experimental cavern at Point 1 of the CERN Large Hadron Collider. During Run 2 of the LHC, a luminosity of ℒ = 2 × 1034 cm-2 s-1 was routinely achieved at the start of fills, twice the design luminosity. For Run 3, accelerator improvements, notably luminosity levelling, allow sustained running at an instantaneous luminosity of ℒ = 2 × 1034 cm-2 s-1, with an average of up to 60 interactions per bunch crossing. The ATLAS detector has been upgraded to recover Run 1 single-lepton trigger thresholds while operating comfortably under Run 3 sustained pileup conditions. A fourth pixel layer 3.3 cm from the beam axis was added before Run 2 to improve vertex reconstruction and b-tagging performance. New Liquid Argon Calorimeter digital trigger electronics, with corresponding upgrades to the Trigger and Data Acquisition system, take advantage of a factor of 10 finer granularity to improve triggering on electrons, photons, taus, and hadronic signatures through increased pileup rejection. The inner muon endcap wheels were replaced by New Small Wheels with Micromegas and small-strip Thin Gap Chamber detectors, providing both precision tracking and Level-1 Muon trigger functionality. Trigger coverage of the inner barrel muon layer near one endcap region was augmented with modules integrating new thin-gap resistive plate chambers and smaller-diameter drift-tube chambers. Tile Calorimeter scintillation counters were added to improve electron energy resolution and background rejection. Upgrades to Minimum Bias Trigger Scintillators and Forward Detectors improve luminosity monitoring and enable total proton-proton cross section, diffractive physics, and heavy ion measurements. These upgrades are all compatible with operation in the much harsher environment anticipated after the High-Luminosity upgrade of the LHC and are the first steps towards preparing ATLAS for the High-Luminosity upgrade of the LHC. This paper describes the Run 3 configuration of the ATLAS detector. © 2024 CERN for the benefit of the ATLAS collaboration.
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| 26. |
- Amerl, M., et al.
(författare)
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Search for nonresonant pair production of Higgs bosons in the Formula Presented final state in pp collisions at Formula Presented with the ATLAS detector
- 2023
-
Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 108:5
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Tidskriftsartikel (refereegranskat)abstract
- A search for nonresonant Higgs boson pair production in the Formula Presented final state is presented. The analysis uses Formula Presented of Formula Presented collision data at Formula Presented collected with the ATLAS detector at the Large Hadron Collider, and targets both the gluon-gluon fusion and vector-boson fusion production modes. No evidence of the signal is found and the observed (expected) upper limit on the cross section for nonresonant Higgs boson pair production is determined to be 5.4 (8.1) times the Standard Model predicted cross section at 95% confidence level. Constraints are placed on modifiers to the Formula Presented and Formula Presented couplings. The observed (expected) Formula Presented constraints on the Formula Presented coupling modifier, Formula Presented, are determined to be Formula Presented (Formula Presented), while the corresponding constraints for the Formula Presented coupling modifier, Formula Presented, are Formula Presented (Formula Presented). In addition, constraints on relevant coefficients are derived in the context of the Standard Model effective field theory and Higgs effective field theory, and upper limits on the Formula Presented production cross section are placed in seven Higgs effective field theory benchmark scenarios. © 2023 CERN, for the ATLAS Collaboration.
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| 27. |
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| 28. |
- Hayrapetyan, A., et al.
(författare)
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Combination of Measurements of the Top Quark Mass from Data Collected by the ATLAS and CMS Experiments at √=7 and 8 TeV
- 2024
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 132:26
-
Tidskriftsartikel (refereegranskat)abstract
- A combination of fifteen top quark mass measurements performed by the ATLAS and CMS experiments at the LHC is presented. The datasets used correspond to an integrated luminosity of up to 5 and Formula Presented of proton-proton collisions at center-of-mass energies of 7 and 8 TeV, respectively. The combination includes measurements in top quark pair events that exploit both the semileptonic and hadronic decays of the top quark, and a measurement using events enriched in single top quark production via the electroweak Formula Presented channel. The combination accounts for the correlations between measurements and achieves an improvement in the total uncertainty of 31% relative to the most precise input measurement. The result is Formula Presented, with a total uncertainty of 0.33 GeV. © 2024 CERN, for the CMS and ATLASs Collaboration.
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| 29. |
- Mullier, G.A., et al.
(författare)
-
A search for new resonances in multiple final states with a high transverse momentum Z boson in √s = 13 TeV pp collisions with the ATLAS detector
- 2023
-
Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2023:6
-
Tidskriftsartikel (refereegranskat)abstract
- A generic search for resonances is performed with events containing a Z boson with transverse momentum greater than 100 GeV, decaying into e + e − or μ + μ −. The analysed data collected with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider correspond to an integrated luminosity of 139 fb −1. Two invariant mass distributions are examined for a localised excess relative to the expected Standard Model background in six independent event categories (and their inclusive sum) to increase the sensitivity. No significant excess is observed. Exclusion limits at 95% confidence level are derived for two cases: a model-independent interpretation of Gaussian-shaped resonances with the mass width between 3% and 10% of the resonance mass, and a specific heavy vector triplet model with the decay mode W′ → ZW → ℓℓqq. [Figure not available: see fulltext.] © 2023, The Author(s).
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| 30. |
- Mullier, G.A., et al.
(författare)
-
Evidence for the charge asymmetry in (Formula presented.) production at √s = 13 TeV with the ATLAS detector
- 2023
-
Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2023:8
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive and differential measurements of the top–antitop (Formula presented.) charge asymmetry (Formula presented.) and the leptonic asymmetry (Formula presented.) are presented in proton–proton collisions at 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 (Formula presented.) charge asymmetry is measured to be (Formula presented.), 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 (Formula presented.) 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. [Figure not available: see fulltext.]. © 2023, The Author(s).
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| 31. |
- Mullier, Geoffrey A., et al.
(författare)
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Measurement of the charge asymmetry in top-quark pair production in association with a photon with the ATLAS experiment
- 2023
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 843
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the charge asymmetry in top-quark pair (tt¯) production in association with a photon is presented. The measurement is performed in the single-lepton tt¯ decay channel using proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN at a centre-of-mass-energy of 13 TeV during the years 2015–2018, corresponding to an integrated luminosity of 139 fb−1. The charge asymmetry is obtained from the distribution of the difference of the absolute rapidities of the top quark and antiquark using a profile likelihood unfolding approach. It is measured to be AC=−0.003±0.029 in agreement with the Standard Model expectation. © 2023 The Author(s)
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| 32. |
- Mullier, Geoffrey A., et al.
(författare)
-
Measurement of the cross-sections of the electroweak and total production of a Zγ pair in association with two jets in pp collisions at √ˆšs=13TeV with the ATLAS detector
- 2023
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 846
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter presents the measurement of the fiducial and differential cross-sections of the electroweakproduction of a Z γ pair in association with two jets. The analysis uses 140 fb−1 of LHC proton–protoncollision data taken at √s=13 TeV recorded by the ATLAS detector during the years 2015–2018. Eventswith a Z boson candidate decaying into either an e+e− or μ+μ− pair, a photon and two jets areselected. The electroweak component is extracted by requiring a large dijet invariant mass and by usingthe information about the centrality of the system and is measured with an observed and expectedsignificance well above five standard deviations. The fiducial pp → Z γ j j cross-section for the electroweakproduction is measured to be 3.6 ± 0.5 fb. The total fiducial cross-section that also includes contributionswhere the jets arise from strong interactions is measured to be 16.8+2.0−1.8 fb. The results are consistentwith the Standard Model predictions. Differential cross-sections are also measured using the same eventsand are compared with parton-shower Monte Carlo simulations. Good agreement is observed betweendata and predictions.
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| 33. |
- Mullier, G.A., et al.
(författare)
-
Measurement of the Higgs boson mass in the H → ZZ⁎ → 4ℓ decay channel using 139 fb−1 of s=13 TeV pp collisions recorded by the ATLAS detector at the LHC
- 2023
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 843
-
Tidskriftsartikel (refereegranskat)abstract
- The mass of the Higgs boson is measured in the H→ZZ⁎→4ℓ decay channel. The analysis uses proton–proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of 139 fb−1. The measured value of the Higgs boson mass is 124.99±0.18(stat.)±0.04(syst.) GeV. In final states with muons, this measurement benefits from an improved momentum-scale calibration relative to that adopted in previous publications. The measurement also employs an analytic model that takes into account the invariant-mass resolution of the four-lepton system on a per-event basis and the output of a deep neural network discriminating signal from background events. This measurement is combined with the corresponding measurement using 7 and 8 TeV pp collision data, resulting in a Higgs boson mass of 124.94±0.17(stat.)±0.03(syst.) GeV. © 2023 The Author(s)
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| 34. |
- Mullier, Geoffrey A., et al.
(författare)
-
Measurement of the Higgs boson mass with H →†’ γγ decays in 140 fb-1 of √ˆšs=13 TeV pp collisions with the ATLAS detector
- 2023
-
Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 847
-
Tidskriftsartikel (refereegranskat)abstract
- The mass of the Higgs boson is measured in the H -> γγ decay channel, exploiting the high resolution of the invariant mass of photon pairs reconstructed from the decays of Higgs bosons produced in proton-proton collisions at a centre-of-mass energy √s = 13 TeV. The dataset was collected between 2015 and 2018 by the ATLAS detector at the Large Hadron Collider, and corresponds to an integrated luminosity of 140 fb-1. The measured value of the Higgs boson mass is 125.17 ± 0.11 (stat.) ± 0.09 (syst.) GeV and is based on an improved energy scale calibration for photons, whose impact on the measurement is about four times smaller than in the previous publication. A combination with the corresponding measurement using 7 and 8 TeV pp collision ATLAS data results in a Higgs boson mass measurement of 125.22 ± 0.11 (stat.) ± 0.09 (syst.) GeV. With an uncertainty of 1.1 per mille, this is currently the most precise measurement of the mass of the Higgs boson from a single decay channel.
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| 35. |
- Mullier, Geoffrey A., et al.
(författare)
-
Measurements of the suppression and correlations of dijets in Xe+Xe collisions at √SNN=5.44 TeV
- 2023
-
Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 108:2
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of the suppression and correlations of dijets is performed using 3 μb-1 of Xe+Xe data at √sNN = 5.44 TeV collected with the ATLAS detector at the CERN Large Hadron Collider. Dijets with jets reconstructed using the R = 0.4 anti-kt algorithm are measured differentially in jet pT over the range of 32 to 398 GeV and the centrality of the collisions. Significant dijet momentum imbalance is found in the most central Xe+Xe collisions, which decreases in more peripheral collisions. Results from the measurement of per-pair normalized and absolutely normalized dijet p(T) balance are compared with previous Pb+Pb measurements at √sNN = 5.02 TeV. The differences between the dijet suppression in Xe+Xe and Pb+Pb are further quantified by the ratio of pair nuclear-modification factors. The results are found to be consistent with those measured in Pb+Pb data when compared in classes of the same event activity and when taking into account the difference between the center-of-mass energies of the initial parton scattering process in Xe+Xe and Pb+Pb collisions. These results should provide input for a better understanding of the role of energy density, system size, path length, and fluctuations in the parton energy loss.
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| 36. |
- Mullier, G.A., et al.
(författare)
-
Observation of the γγ→ττ Process in Pb+Pb Collisions and Constraints on the τ-Lepton Anomalous Magnetic Moment with the ATLAS Detector
- 2023
-
Ingår i: Physical Review Letters. - : American Physical Society (APS). - 1079-7114 .- 0031-9007. ; 131:15
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter reports the observation of τ-lepton-pair production in ultraperipheral lead-lead collisions Pb+Pb→Pb(γγ→ττ)Pb and constraints on the τ-lepton anomalous magnetic moment a_{τ}. The dataset corresponds to an integrated luminosity of 1.44 nb^{-1} of LHC Pb+Pb collisions at sqrt[s_{NN}]=5.02 TeV recorded by the ATLAS experiment in 2018. Selected events contain one muon from a τ-lepton decay, an electron or charged-particle track(s) from the other τ-lepton decay, little additional central-detector activity, and no forward neutrons. The γγ→ττ process is observed in Pb+Pb collisions with a significance exceeding 5 standard deviations and a signal strength of μ_{ττ}=1.03_{-0.05}^{+0.06} assuming the standard model value for a_{τ}. To measure a_{τ}, a template fit to the muon transverse-momentum distribution from τ-lepton candidates is performed, using a dimuon (γγ→μμ) control sample to constrain systematic uncertainties. The observed 95% confidence-level interval for a_{τ} is -0.057
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| 37. |
- Mullier, Geoffrey A., et al.
(författare)
-
Search for lepton-flavour violation in high-mass dilepton final states using 139 fb-1 of pp collisions at √ˆšs=13 TeV with the ATLAS detector
- 2023
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479.
-
Tidskriftsartikel (refereegranskat)abstract
- A search is performed for a heavy particle decaying into different-flavour, dilepton final states, using 139 fb-1 of proton-proton collision data at √s = 13TeV collected in 2015-2018 by the ATLAS detector at the Large Hadron Collider. Final states with electrons, muons and hadronically decaying tau leptons are considered (eμ, eτ or μτ). No significant excess over the Standard Model predictions is observed. Upper limits on the production cross-section are set as a function of the mass of a Z' boson, a supersymmetric τ-sneutrino, and a quantum black-hole. The observed 95% CL lower mass limits obtained on a typical benchmark model Z' boson are 5.0TeV (eμ), 4.0TeV (eτ), and 3.9TeV (μτ), respectively.
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| 38. |
- Mullier, G.A., et al.
(författare)
-
Strong Constraints on Jet Quenching in Centrality-Dependent p+Pb Collisions at 5.02 TeV from ATLAS
- 2023
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 131:7
-
Tidskriftsartikel (refereegranskat)abstract
- Jet quenching is the process of color-charged partons losing energy via interactions with quark-gluon plasma droplets created in heavy-ion collisions. The collective expansion of such droplets is well described by viscous hydrodynamics. Similar evidence of collectivity is consistently observed in smaller collision systems, including p p and p + Pb collisions. In contrast, while jet quenching is observed in Pb + Pb collisions, no evidence has been found in these small systems to date, raising fundamental questions about the nature of the system created in these collisions. The ATLAS experiment at the Large Hadron Collider has measured the yield of charged hadrons correlated with reconstructed jets in 0.36 nb - 1 of p + Pb and 3.6 pb - 1 of p p collisions at 5.02 TeV. The yields of charged hadrons with p T ch > 0.5 GeV near and opposite in azimuth to jets with p T jet > 30 or 60 GeV, and the ratios of these yields between p + Pb and p p collisions, I p Pb , are reported. The collision centrality of p + Pb events is categorized by the energy deposited by forward neutrons from the struck nucleus. The I p Pb values are consistent with unity within a few percent for hadrons with p T ch > 4 GeV at all centralities. These data provide new, strong constraints that preclude almost any parton energy loss in central p + Pb collisions. © 2023 CERN, for the ATLAS Collaboration.
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| 39. |
- Aad, G., et al.
(författare)
-
Study of High-Transverse-Momentum Higgs Boson Production in Association with a Vector Boson in the qqbb Final State with the ATLAS Detector
- 2024
-
Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 132:13
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter presents the first study of Higgs boson production in association with a vector boson (V ¼ W or Z) in the fully hadronic qqbb final state using data recorded by the ATLAS detector at the LHC in proton-proton collisions at √s = 13 TeV and corresponding to an integrated luminosity of 137 fb−1. The vector bosons and Higgs bosons are each reconstructed as large-radius jets and tagged using jet substructure techniques. Dedicated tagging algorithms exploiting b-tagging properties are used to identify jets consistent with Higgs bosons decaying into bb̄. Dominant backgrounds from multijet production are determined directly from the data, and a likelihood fit to the jet mass distribution of Higgs boson candidates is used to extract the number of signal events. The VH production cross section is measured inclusively and differentially in several ranges of Higgs boson transverse momentum: 250–450, 450–650, and greater than 650 GeV. The inclusive signal yield relative to the standard model expectation is observed to be μ = 1.4+1.0−0.9 and the corresponding cross section is 3.1 ± 1.3(stat)+1.8−1.4(syst) pb. © 2024 CERN, for the ATLAS Collaboration.
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| 40. |
- Andersson, Lise-Lotte, et al.
(författare)
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Gamma-ray Spectroscopy of Excited States in 61Zn
- 2006
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Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 30:2, s. 381-390
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Tidskriftsartikel (refereegranskat)abstract
- The Zn-61(30)31 isotope has been produced at the Oak Ridge National Laboratory in the fusion-evaporation reaction Ca-40(Mg-24, 2pn)Zn-61 at 104 MeV. The experimental set-up allowed gamma-rays to be detected in the CLARION Ge detector array in coincidence with the detection of recoiling nuclei in the focal plane at the end of the recoil mass spectrometer. This provides a unique identification of gamma-rays belonging to Zn-61. The excited states have been explored by means of recoil-gamma gamma coincidences, and the resulting decay scheme comprises almost 70 transitions. The data reveal numerous non-yrast states and suggest a revised spin and parity assignment for a previously observed superdeformed band. The resulting decay scheme is compared to predictions from different sets of large-scale shell model calculations.
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| 41. |
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| 42. |
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