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A<sc>bstract</sc> A study of the Higgs boson decaying into bottom quarks (H→$$ b\overline{b} $$ $b\overline{b}$) and charm quarks (H→$$ c\overline{c} $$ $c\overline{c}$) is performed, in the associated production channel of the Higgs boson with aWorZboson, using 140 fb⁻¹of proton-proton collision data at$$ \sqrt{s} $$ $\sqrt{s}$= 13 TeV collected by the ATLAS detector. The individual production ofWHandZHwithH→$$ b\overline{b} $$ $b\overline{b}$is established with observed (expected) significances of 5.3 (5.5) and 4.9 (5.6) standard deviations, respectively. Differential cross-section measurements of the gauge boson transverse momentum within the simplified template cross-section framework are performed in a total of 13 kinematical fiducial regions. The search for theH→$$ c\overline{c} $$ $c\overline{c}$decay yields an observed (expected) upper limit at 95% confidence level of 11.5 (10.6) times the Standard Model prediction. The results are also used to set constraints on the charm coupling modifier, resulting in|κ_c| <4.2 at 95% confidence level. Combining theH→$$ b\overline{b} $$ $b\overline{b}$andH→$$ c\overline{c} $$ $c\overline{c}$measurements constrains the absolute value of the ratio of Higgs-charm and Higgs-bottom coupling modifiers (|κ_c/κ_b|) to be less than 3.6 at 95% confidence level. 

A<sc>bstract</sc> Differential measurements of Higgs boson production in theτ-lepton-pair decay channel are presented in the gluon fusion, vector-boson fusion (VBF),VHand$$ t\overline{t}H $$ $t\overline{t}H$associated production modes, with particular focus on the VBF production mode. The data used to perform the measurements correspond to 140 fb⁻¹of proton-proton collisions collected by the ATLAS experiment at the LHC. Two methods are used to perform the measurements: theSimplified Template Cross-Section(STXS) approach and anUnfolded Fiducial Differentialmeasurement considering only the VBF phase space. For the STXS measurement, events are categorized by their production mode and kinematic properties such as the Higgs boson’s transverse momentum ($$ {p}_{\textrm{T}}^{\textrm{H}} $$ $p_T^H$), the number of jets produced in association with the Higgs boson, or the invariant mass of the two leading jets (m_jj). For the VBF production mode, the ratio of the measured cross-section to the Standard Model prediction form_jj> 1.5 TeV and$$ {p}_{\textrm{T}}^{\textrm{H}} $$ $p_T^H$> 200 GeV ($$ {p}_{\textrm{T}}^{\textrm{H}} $$ $p_T^H$< 200 GeV) is$$ {1.29}_{-0.34}^{+0.39} $$ ${1.29}_{-0.34}^{+0.39}$($$ {0.12}_{-0.33}^{+0.34} $$ ${0.12}_{-0.33}^{+0.34}$). This is the first VBF measurement for the higher-$$ {p}_{\textrm{T}}^{\textrm{H}} $$ $p_T^H$criteria, and the most precise for the lower-$$ {p}_{\textrm{T}}^{\textrm{H}} $$ $p_T^H$criteria. Thefiducialcross-section measurements, which only consider the kinematic properties of the event, are performed as functions of variables characterizing the VBF topology, such as the signed ∆ϕ_jjbetween the two leading jets. The measurements have a precision of 30%–50% and agree well with the Standard Model predictions. These results are interpreted in the SMEFT framework, and place the strongest constraints to date on the CP-odd Wilson coefficient$$ {c}_{H\overset{\sim }{W}} $$ $c_{H\tilde{W}}$. 

A search is performed for dark matter particles produced in association with a resonantly produced pair of b-quarks with 30 < mbb < 150 GeV using 140 fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector at the LHC. This signature is expected in extensions of the standard model predicting the production of dark matter particles, in particular those containing a dark Higgs boson s that decays into bb¯. The highly boosted s → bb¯ topology is reconstructed using jet reclustering and a new identification algorithm. This search places stringent constraints across regions of the dark Higgs model parameter space that satisfy the observed relic density, excluding dark Higgs bosons with masses between 30 and 150 GeV in benchmark scenarios with Z0 mediator masses up to 4.8 TeV at 95% confidence level. 

A<sc>bstract</sc> The paper presents a search for supersymmetric particles produced in proton-proton collisions at$$ \sqrt{s} $$ $\sqrt{s}$= 13 TeV and decaying into final states with missing transverse momentum and jets originating from charm quarks. The data were taken with the ATLAS detector at the Large Hadron Collider at CERN from 2015 to 2018 and correspond to an integrated luminosity of 139 fb⁻¹. No significant excess of events over the expected Standard Model background expectation is observed in optimized signal regions, and limits are set on the production cross-sections of the supersymmetric particles. Pair production of charm squarks or top squarks, each decaying into a charm quark and the lightest supersymmetric particle$$ {\overset{\sim }{\chi}}_1^0 $$ ${\tilde{\chi }}_1^0$, is excluded at 95% confidence level for squarks with masses up to 900 GeV for scenarios where the mass of$$ {\overset{\sim }{\chi}}_1^0 $$ ${\tilde{\chi }}_1^0$is below 50 GeV. Additionally, the production of leptoquarks with masses up to 900 GeV is excluded for the scenario where up-type leptoquarks decay into a charm quark and a neutrino. Model-independent limits on cross-sections and event yields for processes beyond the Standard Model are also reported. 

A<sc>bstract</sc> This paper presents measurements of top-antitop quark pair ($$ t\overline{t} $$ $t\overline{t}$) production in association with additionalb-jets. The analysis utilises 140 fb⁻¹of proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Fiducial cross-sections are extracted in a final state featuring one electron and one muon, with at least three or fourb-jets. Results are presented at the particle level for both integrated cross-sections and normalised differential cross-sections, as functions of global event properties, jet kinematics, andb-jet pair properties. Observable quantities characterisingb-jets originating from the top quark decay and additionalb-jets are also measured at the particle level, after correcting for detector effects. The measured integrated fiducial cross-sections are consistent with$$ t\overline{t}b\overline{b} $$ $t\overline{t}b\overline{b}$predictions from various next-to-leading-order matrix element calculations matched to a parton shower within the uncertainties of the predictions. State-of-the-art theoretical predictions are compared with the differential measurements; none of them simultaneously describes all observables. Differences between any two predictions are smaller than the measurement uncertainties for most observables. 

Z boson events at the Large Hadron Collider can be selected with high purity and are sensitive to a diverse range of QCD phenomena. As a result, these events are often used to probe the nature of the strong force, improve Monte Carlo event generators, and search for deviations from standard model predictions. All previous measurements of Z boson production characterize the event properties using a small number of observables and present the results as differential cross sections in predetermined bins. In this analysis, a machine learning method called omnifold is used to produce a simultaneous measurement of twenty-four Z+jets observables using 139 /fb of proton-proton collisions at sqrt(s) =  TeV collected with the ATLAS detector. Unlike any previous fiducial differential cross-section measurement, this result is presented unbinned as a dataset of particle-level events, allowing for flexible reuse in a variety of contexts and for new observables to be constructed from the twenty-four measured observables. 

This paper describes a measurement of the jet radius dependence of the dijet momentum balance between leading back-to-back jets in $1.72{\mathrm{nb}}^{-1}$of $\text{Pb}+\text{Pb}$collisions collected in 2018 and $255{\mathrm{pb}}^{-1}$of $pp$collisions collected in 2017 by the ATLAS detector at the LHC. Both datasets were collected at $\sqrt{s_{\text{NN}}}=5.02$TeV. Jets are reconstructed using the anti- $k_t$algorithm with jet radius parameters $R=0.2$, 0.3, 0.4, 0.5, and 0.6. The dijet momentum balance distributions are constructed for leading jets with transverse momentum $p_{\text{T}}$from 100 to 562 GeV for $R=0.2$, 0.3, and 0.4 jets, and from 158 to 562 GeV for $R=0.5$and 0.6 jets. The absolutely normalized dijet momentum balance distributions are constructed to compare measurements of the dijet yields in $\text{Pb}+\text{Pb}$collisions directly to the dijet cross sections in $pp$collisions. For all jet radii considered here, there is a suppression of more balanced dijets in $\text{Pb}+\text{Pb}$collisions compared with $pp$collisions, while for more imbalanced dijets there is an enhancement. There is a jet radius dependence to the dijet yields, being stronger for more imbalanced dijets than for more balanced dijets. Additionally, jet pair nuclear modification factors are measured. The subleading jet yields are found to be more suppressed than leading jet yields in dijets. A jet radius dependence of the pair nuclear modification factors is observed, with the suppression decreasing with increasing jet radius. These measurements provide new constraints on jet quenching scenarios in the quark-gluon plasma. ©2024 CERN, for the ATLAS Collaboration2024CERN 

A<sc>bstract</sc> A search is presented for new particles produced in proton-proton collisions at a centre-of-mass energy of 13 TeV that result in final states comprising a massive vector (WorZ) boson that decays hadronically and large missing transverse momentum. The data sample was collected with the ATLAS experiment at the Large Hadron Collider from 2015 to 2018 and corresponds to an integrated luminosity of 140 fb⁻¹. No significant excess over the Standard Model expectation is observed. Model-independent 95% confidence-level limits on the visible cross-section that range from 0.3 fb to 79.5 fb are obtained for non-Standard-Model processes. Exclusion limits are also presented for models with axion-like particles, for two-Higgs-doublet models with a pseudo-scalar mediator between the Standard Model and the dark sector, for the invisible decay of the Higgs boson and for pair-produced weakly interacting dark matter candidates. 

The associated production of Higgs and $W$bosons via vector-boson fusion is highly sensitive to the relative sign of the Higgs boson couplings to $W$and $Z$bosons. In this Letter, two searches for this process are presented, using $140{\mathrm{fb}}^{-1}$of proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$recorded by the ATLAS detector at the LHC. The first search targets scenarios with opposite-sign couplings of the $W$and $Z$bosons to the Higgs boson, while the second targets standard model-like scenarios with same-sign couplings. Both analyses consider Higgs boson decays into a pair of $b$quarks and $W$boson decays with an electron or muon. The data exclude the opposite-sign coupling hypothesis with a significance beyond $5\sigma$, and the observed (expected) upper limit set on the cross section for vector-boson fusion $WH$production is 9.0 (8.7) times the standard model value at 95% confidence level. © 2024 CERN, for the ATLAS Collaboration2024CERN 

This paper presents a search for exotic decays of the Higgs boson into a pair of new pseudoscalar particles, H → aa, where one pseudoscalar decays into a b-quark pair and the other decays into a τ-lepton pair, in the mass range 12 ≤ ma ≤ 60 GeV. The analysis uses pp collision data at \sqrt{s} = 13 TeV collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb−1. No significant excess above the Standard Model (SM) prediction is observed. Assuming the SM Higgs boson production cross section, the search sets upper limits at 95% confidence level on the branching ratio of Higgs bosons decaying into BR (H → aa → bb\tau\tau), between 2.2% and 3.9% depending on the pseudoscalar mass.