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Measurement of the CP properties of Higgs boson interactions with $$\tau $$-leptons with the ATLAS detector

Aad, G. ; Abbott, B. ; Abbott, D. C. ; [et al.]

Springer Science and Business Media LLC ; 2023

In: The European Physical Journal C Vol. 83, No. 7 ( 2023-07-04)

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In: The European Physical Journal C, Springer Science and Business Media LLC, Vol. 83, No. 7 ( 2023-07-04)

Abstract: A study of the charge conjugation and parity ( $$\textit{CP}$$ CP ) properties of the interaction between the Higgs boson and $$\tau $$ τ -leptons is presented. The study is based on a measurement of $$\textit{CP}$$ CP -sensitive angular observables defined by the visible decay products of $$\tau $$ τ -leptons produced in Higgs boson decays. The analysis uses 139 fb $$^{-1}$$ - 1 of proton–proton collision data recorded at a centre-of-mass energy of $$\sqrt{s}= 13$$ s = 13 TeV with the ATLAS detector at the Large Hadron Collider. Contributions from $$\textit{CP}$$ CP -violating interactions between the Higgs boson and $$\tau $$ τ -leptons are described by a single mixing angle parameter $$\phi _{\tau }$$ ϕ τ in the generalised Yukawa interaction. Without constraining the $$H\rightarrow \tau \tau $$ H → τ τ signal strength to its expected value under the Standard Model hypothesis, the mixing angle $$\phi _{\tau }$$ ϕ τ is measured to be $$9^{\circ } \pm 16^{\circ }$$ 9 ∘ ± 16 ∘ , with an expected value of $$0^{\circ } \pm 28^{\circ }$$ 0 ∘ ± 28 ∘ at the 68% confidence level. The pure $$\textit{CP}$$ CP -odd hypothesis is disfavoured at a level of 3.4 standard deviations. The results are compatible with the predictions for the Higgs boson in the Standard Model.

Type of Medium: Online Resource

ISSN: 1434-6052

URL: Article

DOI: 10.1140/epjc/s10052-023-11583-y

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2023

detail.hit.zdb_id: 1397769-6

detail.hit.zdb_id: 1459069-4

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2

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ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset

Aad, G. ; Abbott, B. ; Abbott, D. C. ; [et al.]

Springer Science and Business Media LLC ; 2023

In: The European Physical Journal C Vol. 83, No. 7 ( 2023-07-31)

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In: The European Physical Journal C, Springer Science and Business Media LLC, Vol. 83, No. 7 ( 2023-07-31)

Abstract: The flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of $$\sqrt{s} = 13$$ 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 $$t\bar{t}$$ t t ¯ events; similarly, at a c -jet identification efficiency of 30%, a light-jet ( b -jet) rejection factor of 70 (9) is obtained.

Type of Medium: Online Resource

ISSN: 1434-6052

URL: Article

DOI: 10.1140/epjc/s10052-023-11699-1

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2023

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3

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Measurement of $$Z\gamma \gamma $$ production in pp collisions at $$\sqrt{s}= 13$$ TeV with the ATLAS detector

Aad, G. ; Abbott, B. ; Abbott, D. C. ; [et al.]

Springer Science and Business Media LLC ; 2023

In: The European Physical Journal C Vol. 83, No. 6 ( 2023-06-27)

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In: The European Physical Journal C, Springer Science and Business Media LLC, Vol. 83, No. 6 ( 2023-06-27)

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 $$^{-1}$$ - 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 $$Z(\rightarrow \ell \ell )\gamma \gamma $$ Z ( → ℓ ℓ ) γ γ cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the $$Z\gamma \gamma $$ Z γ γ 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.

Type of Medium: Online Resource

ISSN: 1434-6052

URL: Article

DOI: 10.1140/epjc/s10052-023-11579-8

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2023

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4

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Search for lepton-flavour violation in high-mass dilepton final states using 139 fb−1 of pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

The ATLAS collaboration ; Aad, G. ; Abbott, B. ; [et al.]

Springer Science and Business Media LLC ; 2023

In: Journal of High Energy Physics Vol. 2023, No. 10 ( 2023-10-13)

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In: Journal of High Energy Physics, Springer Science and Business Media LLC, Vol. 2023, No. 10 ( 2023-10-13)

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 $$ \sqrt{s} $$ s = 13 TeV 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 5.0 TeV (e μ ), 4.0 TeV (e τ ), and 3.9 TeV ( μτ ), respectively.

Type of Medium: Online Resource

ISSN: 1029-8479

URL: Article

DOI: 10.1007/JHEP10(2023)082

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2023

detail.hit.zdb_id: 2027350-2

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5

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Search for an axion-like particle with forward proton scattering in association with photon pairs at ATLAS

The ATLAS collaboration ; Aad, G. ; Abbott, B. ; [et al.]

Springer Science and Business Media LLC ; 2023

In: Journal of High Energy Physics Vol. 2023, No. 7 ( 2023-07-31)

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In: Journal of High Energy Physics, Springer Science and Business Media LLC, Vol. 2023, No. 7 ( 2023-07-31)

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 $$ \sqrt{s} $$ 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.

Type of Medium: Online Resource

ISSN: 1029-8479

URL: Article

DOI: 10.1007/JHEP07(2023)234

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2023

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6

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Measurement of the $$ {B}_s^0 $$ → μμ effective lifetime with the ATLAS detector

The ATLAS collaboration ; Aad, G. ; Abbott, B. ; [et al.]

Springer Science and Business Media LLC ; 2023

In: Journal of High Energy Physics Vol. 2023, No. 9 ( 2023-09-28)

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In: Journal of High Energy Physics, Springer Science and Business Media LLC, Vol. 2023, No. 9 ( 2023-09-28)

Abstract: This paper reports the first ATLAS measurement of the $$ {B}_s^0 $$ B s 0 → μμ effective lifetime. The measurement is based on the data collected in 2015–2016, amounting to 26.3 fb − 1 of 13 TeV 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 $$ {B}_s^0 $$ B s 0 effective lifetime, with statistical uncertainties extracted through a Neyman construction. The resulting effective measurement of the $$ {B}_s^0 $$ B s 0 → μμ lifetime is $$ {0.99}_{-0.07}^{+0.42} $$ 0.99 − 0.07 + 0.42 (stat.) ± 0 . 17 (syst.) ps and it is found to be consistent with the Standard Model.

Type of Medium: Online Resource

ISSN: 1029-8479

URL: Article

DOI: 10.1007/JHEP09(2023)199

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2023

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7

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Search for direct pair production of sleptons and charginos decaying to two leptons and neutralinos with mass splittings near the W-boson mass in $$ \sqrt{s} $$ = 13 TeV pp collisions with the ATLAS detector

The ATLAS collaboration ; Aad, G. ; Abbott, B. ; [et al.]

Springer Science and Business Media LLC ; 2023

In: Journal of High Energy Physics Vol. 2023, No. 6 ( 2023-06-06)

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In: Journal of High Energy Physics, Springer Science and Business Media LLC, Vol. 2023, No. 6 ( 2023-06-06)

Abstract: A search for the electroweak production of pairs of charged sleptons or charginos decaying into two-lepton final states with missing transverse momentum is presented. Two simplified models of R -parity-conserving supersymmetry are considered: direct pair-production of sleptons $$ \left(\overset{\sim }{\ell}\overset{\sim }{\ell}\right) $$ ℓ ~ ℓ ~ , with each decaying into a charged lepton and a $$ {\overset{\sim }{\chi}}_1^0 $$ χ ~ 1 0 neutralino, and direct pair-production of the lightest charginos $$ \left({\overset{\sim }{\chi}}_1^{\pm }{\overset{\sim }{\chi}}_1^{\mp}\right) $$ χ ~ 1 ± χ ~ 1 ∓ , with each decaying into a W -boson and a $$ {\overset{\sim }{\chi}}_1^0 $$ χ ~ 1 0 . The lightest neutralino $$ \left({\overset{\sim }{\chi}}_1^0\right) $$ χ ~ 1 0 is assumed to be the lightest supersymmetric particle (LSP). The analyses target the experimentally challenging mass regions where $$ m\left(\overset{\sim }{\ell}\right)-m\left({\overset{\sim }{\chi}}_1^0\right) $$ m ℓ ~ − m χ ~ 1 0 and $$ m\left({\overset{\sim }{\chi}}_1^{\pm}\right)-m\left({\overset{\sim }{\chi}}_1^0\right) $$ m χ ~ 1 ± − m χ ~ 1 0 are close to the W -boson mass (‘moderately compressed’ regions). The search uses 139 fb − 1 of $$ \sqrt{s} $$ s = 13 TeV proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. No significant excesses over the expected background are observed. Exclusion limits on the simplified models under study are reported in the $$ \left(\overset{\sim }{\ell },{\overset{\sim }{\chi}}_1^0\right) $$ ℓ ~ χ ~ 1 0 and $$ \left({\overset{\sim }{\chi}}_1^{\pm }{\overset{\sim }{\chi}}_1^0\right) $$ χ ~ 1 ± χ ~ 1 0 mass planes at 95% confidence level (CL). Sleptons with masses up to 150 GeV are excluded at 95% CL for the case of a mass-splitting between sleptons and the LSP of 50 GeV. Chargino masses up to 140 GeV are excluded at 95% CL for the case of a mass-splitting between the chargino and the LSP down to about 100 GeV.

Type of Medium: Online Resource

ISSN: 1029-8479

URL: Article

DOI: 10.1007/JHEP06(2023)031

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2023

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8

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Search for dark photons from Higgs boson decays via ZH production with a photon plus missing transverse momentum signature from pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

The ATLAS collaboration ; Aad, G. ; Abbott, B. ; [et al.]

Springer Science and Business Media LLC ; 2023

In: Journal of High Energy Physics Vol. 2023, No. 7 ( 2023-07-17)

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In: Journal of High Energy Physics, Springer Science and Business Media LLC, Vol. 2023, No. 7 ( 2023-07-17)

Abstract: This paper describes a search for dark photons ( γ d ) in proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV at the Large Hadron Collider (LHC). The dark photons are searched for in the decay of Higgs bosons ( H → γγ d ) 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 γ d , 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 → γγ d ) of 2.28% ( $$ {2.82}_{-0.84}^{+1.33}\% $$ 2.82 − 0.84 + 1.33 % ) is set at 95% CL for massless γ d . For massive dark photons up to 40 GeV, the observed (expected) upper limits on BR( H → γγ d ) at 95% confidence level is found within the [2.19,2.52]% ([2.71,3.11] %) range.

Type of Medium: Online Resource

ISSN: 1029-8479

URL: Article

DOI: 10.1007/JHEP07(2023)133

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2023

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9

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Search for new phenomena in multi-body invariant masses in events with at least one isolated lepton and two jets using $$ \sqrt{s} $$ = 13 TeV proton–proton collision data collected by the ATLAS detector

The ATLAS collaboration ; Aad, G. ; Abbott, B. ; [et al.]

Springer Science and Business Media LLC ; 2023

In: Journal of High Energy Physics Vol. 2023, No. 7 ( 2023-07-26)

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In: Journal of High Energy Physics, Springer Science and Business Media LLC, Vol. 2023, No. 7 ( 2023-07-26)

Abstract: A search for resonances in events with at least one isolated lepton ( e or μ ) and two jets is performed using 139 fb − 1 of $$ \sqrt{s} $$ s = 13 TeV proton–proton collision data recorded by the ATLAS detector at the LHC. Deviations from a smoothly falling background hypothesis are tested in three- and four-body invariant mass distributions constructed from leptons and jets, including jets identified as originating from bottom quarks. Model-independent limits on generic resonances characterised by cascade decays of particles leading to multiple jets and leptons in the final state are presented. The limits are calculated using Gaussian shapes with different widths for the invariant masses. The multi-body invariant masses are also used to set 95% confidence level upper limits on the cross-section times branching ratios for the production and subsequent decay of resonances predicted by several new physics scenarios.

Type of Medium: Online Resource

ISSN: 1029-8479

URL: Article

DOI: 10.1007/JHEP07(2023)202

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2023

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10

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Search for a new scalar resonance in flavour-changing neutral-current top-quark decays t → qX (q = u, c), with X → $$ b\overline{b} $$, in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

The ATLAS collaboration ; Aad, G. ; Abbott, B. ; [et al.]

Springer Science and Business Media LLC ; 2023

In: Journal of High Energy Physics Vol. 2023, No. 7 ( 2023-07-26)

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In: Journal of High Energy Physics, Springer Science and Business Media LLC, Vol. 2023, No. 7 ( 2023-07-26)

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 → $$ b\overline{b} $$ b b ¯ , 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 13 TeV, 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 $$ \mathcal{B} $$ B ( t → uX ) and between 0.018% and 0.078% for the branching fraction $$ \mathcal{B} $$ B ( t → cX ), for masses of the scalar particle X between 20 and 160 GeV.

Type of Medium: Online Resource

ISSN: 1029-8479

URL: Article

DOI: 10.1007/JHEP07(2023)199

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2023

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