Date

Measurement of jet track functions in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Aakvaag, Erlend ; Abbott, Braden Keim ; et al.
Phys.Lett.B 868 (2025) 139680, 2025.
Inspire Record 2875457 DOI 10.17182/hepdata.153882

Measurements of jet substructure are key to probing the energy frontier at colliders, and many of them use track-based observables which take advantage of the angular precision of tracking detectors. Theoretical calculations of track-based observables require `track functions', which characterize the transverse momentum fraction $r_q$ carried by charged hadrons from a fragmenting quark or gluon. This letter presents a direct measurement of $r_q$ distributions in dijet events from the 140 fb$^{-1}$ of proton--proton collisions at $\sqrt{s}=13$ TeV recorded with the ATLAS detector. The data are corrected for detector effects using machine-learning methods. The scale evolution of the moments of the $r_q$ distribution is sensitive to non-linear renormalization group evolution equations of QCD, and is compared with analytic predictions. When incorporated into future theoretical calculations, these results will enable a precision program of theory-data comparison for track-based jet substructure observables.

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$r_{q}$, Gluon jets, $240\text{GeV} \leq p_T < 300~\text{GeV}$, Gluon $\eta$, Fig 5

$r_{q}$, Gluon jets, $300~\text{GeV} \leq p_T < 400~\text{GeV}$, Gluon $\eta$, Fig 5

$r_{q}$, Gluon jets, $400~\text{GeV} \leq p_T < 500~\text{GeV}$, Gluon $\eta$, Fig 5

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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

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, D.C. ; et al.
Phys.Rev.C 107 (2023) 054910, 2023.
Inspire Record 2075412 DOI 10.17182/hepdata.139082

The correlations between flow harmonics $v_n$ for $n=2$, 3 and 4 and mean transverse momentum $[p_\mathrm{T}]$ in $^{129}$Xe+$^{129}$Xe and $^{208}$Pb+$^{208}$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV and 5.02 TeV, respectively, are measured using charged particles with the ATLAS detector. The correlations are sensitive to the shape and size of the initial geometry, nuclear deformation, and initial momentum anisotropy. The effects from non-flow and centrality fluctuations are minimized, respectively, via a subevent cumulant method and event activity selection based on particle production in the very forward rapidity. The results show strong dependences on centrality, harmonic number $n$, $p_{\mathrm{T}}$ and pseudorapidity range. Current models describe qualitatively the overall centrality- and system-dependent trends but fail to quantitatively reproduce all the data. In the central collisions, where models generally show good agreement, the $v_2$-$[p_\mathrm{T}]$ correlations are sensitive to the triaxiality of the quadruple deformation. The comparison of model to the Pb+Pb and Xe+Xe data suggests that the $^{129}$Xe nucleus is a highly deformed triaxial ellipsoid that is neither a prolate nor an oblate shape. This provides strong evidence for a triaxial deformation of $^{129}$Xe nucleus using high-energy heavy-ion collision.

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$\rho_{2}$ Standard method, for Pb+Pb 5.02 TeV, $|\eta|$<2.5, 0.5< $p_{T}$ <5.0 GeV vs $\Sigma E_{T}$ based Centrality

$\rho_{2}$ Two_subevent method, for Pb+Pb 5.02 TeV, $|\eta|$<2.5, 0.5< $p_{T}$ <5.0 GeV vs $\Sigma E_{T}$ based Centrality

$\rho_{2}$ Three_subevent method, for Pb+Pb 5.02 TeV, $|\eta|$<2.5, 0.5< $p_{T}$ <5.0 GeV vs $\Sigma E_{T}$ based Centrality

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Measurements of the production cross-sections of a Higgs boson in association with a vector boson and decaying into $WW^\ast$ with the ATLAS detector at $\sqrt{s} = 13$ TeV

The ATLAS collaboration Aad, Georges ; Aakvaag, Erlend ; Abbott, Braden Keim ; et al.
JHEP 08 (2025) 034, 2025.
Inspire Record 2905253 DOI 10.17182/hepdata.157861

Measurements of the total and differential Higgs boson production cross-sections, via $WH$ and $ZH$ associated production using $H\rightarrow WW^\ast\rightarrow\ellν\ellν$ and $H\rightarrow WW^\ast\rightarrow\ellνjj$ decays, are presented. The analysis uses proton-proton events delivered by the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector between 2015 and 2018. The data correspond to an integrated luminosity of 140 fb$^{-1}$. The sum of the $WH$ and $ZH$ cross-sections times the $H\rightarrow WW^\ast$ branching fraction is measured to be $0.44^{+0.10}_{-0.09}$ (stat.) $^{+0.06}_{-0.05}$ (syst.) pb, in agreement with the Standard Model prediction. Higgs boson production is further characterised through measurements of the differential cross-section as a function of the transverse momentum of the vector boson and in the framework of Simplified Template Cross-Sections.

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Post-fit distribution of $ANN_{Zdom}$ in the Z-dominated SR. The post-fit result is obtained from the combined 2-POI fit described in section 9.1 of the paper.

Best-fit values of the total $WH$, $ZH$, and $VH$ cross sections times the $H\rightarrow WW^{*}$ branching ratio.

Observed profile likelihood as a function of $\sigma\times\mathcal{B}_{H\rightarrow WW^{*}}$ normalised by the SM expectation for the $VH$ and $WH/ZH$ measurements from the combined 1- and 2-POI fits, respectively

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Evidence for the collective nature of radial flow in Pb+Pb collisions with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Aakvaag, Erlend ; Abbott, Braden Keim ; et al.
CERN-EP-2025-068, 2025.
Inspire Record 2907010 DOI 10.17182/hepdata.158359

Anisotropic flow and radial flow are two key probes of the expansion dynamics and properties of the quark-gluon plasma (QGP). While anisotropic flow has been extensively studied, radial flow, which governs the system's radial expansion, has received less attention. Notably, experimental evidence for the global and collective nature of radial flow has been lacking. This Letter presents the first measurement of transverse momentum ($p_{\mathrm{T}}$) dependence of radial flow fluctuations ($v_0(p_{\mathrm{T}})$) over $0.5<p_{\mathrm{T}}<10$ GeV, using a two-particle correlation method in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. The data reveal three key features supporting the collective nature of radial flow: long-range correlation in pseudorapidity, factorization in $p_{\mathrm{T}}$, and centrality-independent shape in $p_{\mathrm{T}}$. The comparison with a hydrodynamic model demonstrates the sensitivity of $v_0(p_{\mathrm{T}})$ to bulk viscosity, a crucial transport property of the QGP. These findings establish a new, powerful tool for probing collective dynamics and properties of the QGP.

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Data from Figure 2, panel a, $v_{0}$

Data from Figure 2, panel c, upper panel, Normalized Covariance $\times 10^{3}$ in 0-5% Centrality

Data from Figure 2, panel c, lower panel, Normalized Covariance $\times 10^{3}$ in 50-60% Centrality

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Version 2
A measurement of the high-mass $τ\barτ$ production cross-section at $\sqrt{s}=13$ TeV with the ATLAS detector and constraints on new particles and couplings

The ATLAS collaboration Aad, Georges ; Aakvaag, Erlend ; Abbott, Braden Keim ; et al.
JHEP 10 (2025) 054, 2025.
Inspire Record 2905252 DOI 10.17182/hepdata.155470

The production cross-section of high-mass $τ$-lepton pairs is measured as a function of the dilepton visible invariant mass, using 140 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider. The measurement agrees with the predictions of the Standard Model. A fit to the invariant mass distribution is performed as a function of $b$-jet multiplicity, to constrain the non-resonant production of new particles described by an effective field theory or in models containing leptoquarks or $Z'$ bosons that couple preferentially to third-generation fermions. The constraints on new particles improve on previous results, and the constraints on effective operators include those affecting the anomalous magnetic moment of the $τ$-lepton.

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The measured unfolded differential cross sections.

The measured unfolded differential cross sections.

The combined covariance matrix for the differential cross-section distribution.

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Search for $t\bar{t}H/A \rightarrow t\bar{t}t\bar{t}$ production in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Aakvaag, Erlend ; Abbott, Braden Keim ; et al.
Eur.Phys.J.C 85 (2025) 573, 2025.
Inspire Record 2823281 DOI 10.17182/hepdata.158356

A search is presented for a heavy scalar ($H$) or pseudo-scalar ($A$) predicted by the two-Higgs-doublet models, where the $H/A$ is produced in association with a top-quark pair ($t\bar{t}H/A$), and with the $H/A$ decaying into a $t\bar{t}$ pair. Events are selected requiring exactly one or two opposite-charge electrons or muons. Data-driven corrections are applied to improve the modelling of the $t\bar{t}$+jets background in the regime with high jet and $b$-jet multiplicities. These include a novel multi-dimensional kinematic reweighting based on a neural network trained using data and simulations. An $H/A$-mass parameterised graph neural network is trained to optimise the signal-to-background discrimination. In combination with the previous search performed by the ATLAS Collaboration in the multilepton final state, the observed upper limits on the $t\bar{t}H/A \rightarrow t\bar{t}t\bar{t}$ production cross-section at 95% confidence level range between 14 fb and 5.0 fb for an $H/A$ with mass between 400 GeV and 1000 GeV, respectively. Assuming that both the $H$ and $A$ contribute to the $t\bar{t}t\bar{t}$ cross-section, $\tanβ$ values below 1.7 or 0.7 are excluded for a mass of 400 GeV or 1000 GeV, respectively. The results are also used to constrain a model predicting the pair production of a colour-octet scalar, with the scalar decaying into a $t\bar{t}$ pair.

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Post-fit distribution of the GNN score evaluated with $m_{H/A}$ = 400 GeV in the 1L region with $\geq 10$ jets and four $b$-tagged jets. The fit is performed under the background-only hypothesis.

Post-fit distribution of the GNN score evaluated with $m_{H/A}$ = 400 GeV in the 2LOS region with $\geq8$ jets and $\geq 4$ $𝑏$-tagged jets. The fit is performed under the background-only hypothesis.

Post-fit distribution of the GNN score evaluated with $m_{H/A}$ = 400 GeV in the validation region in the 1L region with $\geq 10$ jets. These regions do not enter the fit. The post-fit background prediction is obtained using the post-fit nuisance parameters from the background-only fit in the control and signal regions.

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Search for events with one displaced vertex from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in $pp$ collisions at $\sqrt{s}=13$ TeV

The ATLAS collaboration Aad, Georges ; Aakvaag, Erlend ; Abbott, Braden Keim ; et al.
Phys.Rev.D 112 (2025) 092001, 2025.
Inspire Record 2905251 DOI 10.17182/hepdata.158373

A search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using 140 fb$^{-1}$ of proton-proton collision data at $\sqrt{s} = 13$ TeV recorded in 2015-2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axion-like particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photo-phobic axion-like particle model considered, this search produces the strongest limits to date for proper decay lengths greater than $\mathcal{O}(10)$ cm.

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Summary of the one-DV limits for the H/ϕ arrow ss model. Comparison between observed and expected 95% CL limits on (σ/σggH)×B for an SM-like Higgs boson portal mediator and ms=35 GeV. The observed limits are consistent with the expected ones within the uncertainties.

Observed 95% CL limits on (σ/σggH)×B for all Higgs boson portal mediator samples where the cross-section is normalized to the SM Higgs boson gluon–gluon fusion production cross-section, σggH = 48.61 pb [97]. The observed limits are consistent with the expected ones within the uncertainties.

Observed 95% CL limits on σ×B for mϕ≠ 125 GeV. The observed limits are consistent with the expected ones within the uncertainties.

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Measurement of photonuclear jet production in ultra-peripheral Pb+Pb collisions at $\sqrt{s_{\text{NN}}} = 5.02$ TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Aakvaag, Erlend ; Abbott, Braden Keim ; et al.
Phys.Rev.D 111 (2025) 052006, 2025.
Inspire Record 2829427 DOI 10.17182/hepdata.156979

In ultra-relativistic heavy ion collisions at the LHC, each nucleus acts a sources of high-energy real photons that can scatter off the opposing nucleus in ultra-peripheral photonuclear ($\gamma+A$) collisions. Hard scattering processes initiated by the photons in such collisions provide a novel method for probing nuclear parton distributions in a kinematic region not easily accessible to other measurements. ATLAS has measured production of dijet and multi-jet final states in ultra-peripheral Pb+Pb collisions at $\sqrt{s_{\text{NN}}} = 5.02$ TeV using a data set recorded in 2018 with an integrated luminosity of 1.72 $\text{nb}^{-1}$. Photonuclear final states are selected by requiring a rapidity gap in the photon direction; this selects events where one of the outgoing nuclei remains intact. Jets are reconstructed using the anti-$k_\text{t}$ algorithm with radius parameter, $R = 0.4$. Triple-differential cross-sections, unfolded for detector response, are measured and presented using two sets of kinematic variables. The first set consists of the total transverse momentum ($H_\text{T}$),rapidity, and mass of the jet system. The second set uses $H_\text{T}$ and particle-level nuclear and photon parton momentum fractions, $x_\text{A}$ and $z_{\gamma}$, respectively. The results are compared with leading-order (LO) perturbative QCD calculations of photonuclear jet production cross-sections, where all LO predictions using existing fits fall below the data in the shadowing region. More detailed theoretical comparisons will allow these results to strongly constrain nuclear parton distributions, and these data provide results from the LHC directly comparable to early physics results at the planned Electron-Ion Collider.

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The fraction of photonuclear jet events passing the fiducial requirements in which the photon-emitting nucleus does not break up as a function of \zg. The systematic uncertainties are not symmetrized, and correlations in uncertainties are neglected for both the total systematic uncertainty and statistical uncertainty.

Fully unfolded triple-differential cross-sections as a function of $H_\text{T}$, $y_\text{jets}$, and $m_\text{jets}$. Systematic uncertainties are decomposed into symmetrized nuisance parameters, where parameters labelled "Corr" are fully correlated bin-to-bin, while parameters labelled "Uncorr" should be treated as un-correlated bin-to-bin. These cross-sections are not corrected for the effects of additional nuclear break-up. Values for the total fiducial cross-section in each bin are reported with full statistical and systematic uncertainties. Fractions of the total bin volume occupied by the fiducial region, fractions of the total cross-section in that bin satisfying fiducial requirements, and mean bin values for each axis variable are derived from Pythia 8 Monte Carlo and reported as well. For more details on these quantities, see Appendix B.

Fully unfolded triple-differential cross-sections as a function of $H_\text{T}$, $x_\text{A}$, and $z_{\gamma}$. Systematic uncertainties are decomposed into symmetrized nuisance parameters, where parameters labelled "Corr" are fully correlated bin-to-bin, while parameters labelled "Uncorr" should be treated as un-correlated bin-to-bin. These cross-sections are not corrected for the effects of additional nuclear break-up. Values for the total fiducial cross-section in each bin are reported with full statistical and systematic uncertainties. Fractions of the total bin volume occupied by the fiducial region, fractions of the total cross-section in that bin satisfying fiducial requirements, and mean bin values for each axis variable are derived from Pythia 8 Monte Carlo and reported as well. For more details on these quantities, see Appendix B.


Observation of $t\bar{t}$ production in the lepton+jets and dilepton channels in $p$+Pb collisions at $\sqrt{s_\mathrm{NN}}=8.16$ TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Aakvaag, Erlend ; Abbott, Braden Keim ; et al.
JHEP 11 (2024) 101, 2024.
Inspire Record 2784411 DOI 10.17182/hepdata.153893

This paper reports the observation of top-quark pair production in proton-lead collisions in the ATLAS experiment at the Large Hadron Collider. The measurement is performed using 165 nb$^{-1}$ of $p$+Pb data collected at $\sqrt{s_\mathrm{NN}}=8.16$ TeV in 2016. Events are categorised in two analysis channels, consisting of either events with exactly one lepton (electron or muon) and at least four jets, or events with two opposite-charge leptons and at least two jets. In both channels at least one $b$-tagged jet is also required. Top-quark pair production is observed with a significance over five standard deviations in each channel. The top-quark pair production cross-section is measured to be $\sigma_{t\bar{t}}= 58.1\pm 2.0\;\mathrm{(stat.)\;^{+4.8}_{-4.4} \;\mathrm{(syst.)}}\;\mathrm{nb}$, with a total uncertainty of 9%. In addition, the nuclear modification factor is measured to be $R_{p\mathrm{A}} = 1.090\pm0.039\;(\mathrm{stat.})\;^{+0.094}_{-0.087}\;(\mathrm{syst.})$. The measurements are found to be in good agreement with theory predictions involving nuclear parton distribution functions.

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Measurements of $W^+W^-$ production cross-sections in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abeling, Kira ; et al.
JHEP 08 (2025) 142, 2025.
Inspire Record 2923238 DOI 10.17182/hepdata.156818

Measurements of $W^+W^-\rightarrow e^\pm νμ^\mp ν$ production cross-sections are presented, providing a test of the predictions of perturbative quantum chromodynamics and the electroweak theory. The measurements are based on data from $pp$ collisions at $\sqrt{s}=13$ TeV recorded by the ATLAS detector at the Large Hadron Collider in 2015-2018, corresponding to an integrated luminosity of 140 fb$^{-1}$. The number of events due to top-quark pair production, the largest background, is reduced by rejecting events containing jets with $b$-hadron decays. An improved methodology for estimating the remaining top-quark background enables a precise measurement of $W^+W^-$ cross-sections with no additional requirements on jets. The fiducial $W^+W^-$ cross-section is determined in a maximum-likelihood fit with an uncertainty of 3.1%. The measurement is extrapolated to the full phase space, resulting in a total $W^+W^-$ cross-section of $127\pm4$ pb. Differential cross-sections are measured as a function of twelve observables that comprehensively describe the kinematics of $W^+W^-$ events. The measurements are compared with state-of-the-art theory calculations and excellent agreement with predictions is observed. A charge asymmetry in the lepton rapidity is observed as a function of the dilepton invariant mass, in agreement with the Standard Model expectation. A CP-odd observable is measured to be consistent with no CP violation. Limits on Standard Model effective field theory Wilson coefficients in the Warsaw basis are obtained from the differential cross-sections.

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Measured fiducial cross-section compared with theoretical predictions from MiNNLO+Pythia8, Geneva+Pythia8, Sherpa2.2.12, and MATRIX2.1. The predictions are based on the NNPDF3.0 (red squares) and NNPDF3.1 luxQED (blue dots) PDF sets. The nNNLO predictions include photon-induced contributions (always using NNPDF3.1 luxQED) and NLO QCD corrections to the gluon-gluon initial state. The $q\bar{q}\rightarrow WW$ predictions from MiNNLO, Geneva, and Sherpa2.2.12 are combined with a Sherpa2.2.2 prediction of gluon-induced production, scaled by an inclusive NLO K-factor of 1.7. Inner (outer) error bars on the theory predictions correspond to PDF (the combination of scale and PDF) uncertainties. The MATRIX nNNLO QCD $\otimes$ NLO EW prediction using NNPDF3.1 luxQED, the best available prediction of the integrated fiducial cross-section, is in good agreement with the measurement.

Fiducial differential cross-sections as a function of $p_{\mathrm{T}}^{\mathrm{lead.\,lep.}}$. The measured cross-section values are shown as points with error bars giving the statistical uncertainty and solid bands indicating the size of the total uncertainty. The right-hand-side axis indicates the integrated cross-section of the rightmost bin. The results are compared to fixed-order nNNLO QCD + NLO EW predictions of Matrix 2.1, with the NNLO + PS predictions from Powheg MiNNLO + Pythia8 and Geneva + Pythia8, as well as Sherpa2.2.12 NLO + PS predictions. The last three predictions are combined with Sherpa 2.2.2 for the $gg$ initial state and Sherpa 2.2.12 for electroweak $WWjj$ production. These contributions are modelled at LO but a NLO QCD $k$-factor of 1.7 is applied for gluon induced production. Theoretical predictions are indicated as markers with vertical lines denoting PDF, scale and parton shower uncertainties. Markers are staggered for better visibility.

Correlation matrix of the statistical uncertainties in the measured fiducial cross section for the observable $p_{\mathrm{T}}^{\mathrm{lead.\,lep.}}$.

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