Several extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with $VV=W^\pm W^\mp$ or $ZZ$ pairs from a decay of a dark Higgs boson $s$ is searched for using 139 fb$^{-1}$ of $pp$ collisions recorded by the ATLAS detector at a center-of-mass energy of 13 TeV. The $s\to V(q\bar q)V(q\bar q)$ decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted $VV$ pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with $m_s > 160$ GeV are excluded.
Data overlaid on SM background post-fit yields stacked in each SR and CR category and E<sub>T</sub><sup>miss</sup> bin with the maximum-likelihood estimators set to the conditional values of the CR-only fit, and propagated to SR and CRs. Pre-fit uncertainties cover differences between the data and pre-fit background prediction.
Dominant sources of uncertainty for three dark Higgs scenarios after the fit to Asimov data generated from the expected values of the maximum-likelihood estimators including predicted signals with m<sub>Z'</sub> = 1 TeV and m<sub>s</sub> of (a) 160 GeV, (b) 235 GeV, and (c) 310 GeV. The uncertainty in the fitted signal yield relative to the theory prediction is presented. Total is the quadrature sum of statistical and total systematic uncertainties, which consider correlations.
The ratios (μ) of the 95% C.L. upper limits on the combined s→ W<sup>±</sup>W<sup>∓</sup> and s→ ZZ cross section to simplified model expectations for the m<sub>Z'</sub>=0.5 TeV scenario, for various m<sub>s</sub> hypotheses. The observed limits (solid line) are consistent with the expectation under the SM-only hypothesis (dashed line) within uncertainties (filled band), except for a small excess for m<sub>s</sub>=160 GeV, discussed in the text.
Narrow resonances decaying into $WW$, $WZ$ or $ZZ$ boson pairs are searched for in 139 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of $\sqrt{s}=13$ TeV recorded with the ATLAS detector at the Large Hadron Collider from 2015 to 2018. The diboson system is reconstructed using pairs of high transverse momentum, large-radius jets. These jets are built from a combination of calorimeter- and tracker-inputs compatible with the hadronic decay of a boosted $W$ or $Z$ boson, using jet mass and substructure properties. The search is performed for diboson resonances with masses greater than 1.3 TeV. No significant deviations from the background expectations are observed. Exclusion limits at the 95% confidence level are set on the production cross-section times branching ratio into dibosons for resonances in a range of theories beyond the Standard Model, with the highest excluded mass of a new gauge boson at 3.8 TeV in the context of mass-degenerate resonances that couple predominantly to gauge bosons.
Limit Plot
Limit Plot
Limit Plot
A novel search for exotic decays of the Higgs boson into pairs of long-lived neutral particles, each decaying into a bottom quark pair, is performed using 139 fb$^{-1}$ of $\sqrt{s} = 13$ TeV proton-proton collision data collected with the ATLAS detector at the LHC. Events consistent with the production of a Higgs boson in association with a leptonically decaying $Z$ boson are analysed. Long-lived particle (LLP) decays are reconstructed from inner-detector tracks as displaced vertices with high mass and track multiplicity relative to Standard Model processes. The analysis selection requires the presence of at least two displaced vertices, effectively suppressing Standard Model backgrounds. The residual background contribution is estimated using a data-driven technique. No excess over Standard Model predictions is observed, and upper limits are set on the branching ratio of the Higgs boson to LLPs. Branching ratios above 10% are excluded at 95% confidence level for LLP mean proper lifetimes $c\tau$ as small as 4 mm and as large as 100 mm. For LLP masses below 40 GeV, these results represent the most stringent constraint in this lifetime regime.
95% CL exclusion limits on $\mathcal{B}(H\rightarrow aa \rightarrow b\bar{b}b\bar{b})$ for $m_a = 16$ GeV.
95% CL exclusion limits on $\mathcal{B}(H\rightarrow aa \rightarrow b\bar{b}b\bar{b})$ for $m_a = 25$ GeV.
95% CL exclusion limits on $\mathcal{B}(H\rightarrow aa \rightarrow b\bar{b}b\bar{b})$ for $m_a = 35$ GeV.
The production of dark matter in association with Higgs bosons is predicted in several extensions of the Standard Model. An exploration of such scenarios is presented, considering final states with missing transverse momentum and $b$-tagged jets consistent with a Higgs boson. The analysis uses proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment at the LHC during Run 2, amounting to an integrated luminosity of 139 fb$^{-1}$. The analysis, when compared with previous searches, benefits from a larger dataset, but also has further improvements providing sensitivity to a wider spectrum of signal scenarios. These improvements include both an optimised event selection and advances in the object identification, such as the use of the likelihood-based significance of the missing transverse momentum and variable-radius track-jets. No significant deviation from Standard Model expectations is observed. Limits are set, at 95% confidence level, in two benchmark models with two Higgs doublets extended by either a heavy vector boson $Z'$ or a pseudoscalar singlet $a$ and which both provide a dark matter candidate $\chi$. In the case of the two-Higgs-doublet model with an additional vector boson $Z'$, the observed limits extend up to a $Z'$ mass of 3 TeV for a mass of 100 GeV for the dark matter candidate. The two-Higgs-doublet model with a dark matter particle mass of 10 GeV and an additional pseudoscalar $a$ is excluded for masses of the $a$ up to 520 GeV and 240 GeV for $\tan \beta = 1$ and $\tan \beta = 10$ respectively. Limits on the visible cross-sections are set and range from 0.05 fb to 3.26 fb, depending on the missing transverse momentum and $b$-quark jet multiplicity requirements.
<b>- - - - - - - - Overview of HEPData Record - - - - - - - -</b> <br><br> <b>Exclusion contours:</b> <ul> <li><a href="?table=LimitContour_ZP2HDM_obs">Observed 95% CL exclusion limit for the Z'-2HDM model</a> <li><a href="?table=LimitContour_ZP2HDM_exp">Expected 95% CL exclusion limit for the Z'-2HDM model</a> <li><a href="?table=LimitContour_ZP2HDM_exp_1s">Expected +- 1sigma 95% CL exclusion limit for the Z'-2HDM model</a> <li><a href="?table=LimitContour_ZP2HDM_exp_2s">Expected +- 2sigma 95% CL exclusion limit for the Z'-2HDM model</a> <li><a href="?table=LimitContour_2HDMa_tb1_sp0p35_obs">Observed 95% CL exclusion limit for ggF production in the 2HDM+a model</a> <li><a href="?table=LimitContour_2HDMa_tb1_sp0p35_exp">Expected 95% CL exclusion limit for ggF production in the 2HDM+a model</a> <li><a href="?table=LimitContour_2HDMa_tb1_sp0p35_exp_1s">Expected +- 1 sigma 95% CL exclusion limit for ggF production in the 2HDM+a model</a> <li><a href="?table=LimitContour_2HDMa_tb1_sp0p35_exp_2s">Expected +- 2 sigma 95% CL exclusion limit for ggF production in the 2HDM+a model</a> <li><a href="?table=LimitContour_2HDMa_tb10_sp0p35_obs">Observed 95% CL exclusion limit for bbA production in the 2HDM+a model</a> <li><a href="?table=LimitContour_2HDMa_tb10_sp0p35_exp">Expected 95% CL exclusion limit for bbA production in the 2HDM+a model</a> <li><a href="?table=LimitContour_2HDMa_tb10_sp0p35_exp_1s">Expected +- 1 sigma 95% CL exclusion limit for bbA production in the 2HDM+a model</a> <li><a href="?table=LimitContour_2HDMa_tb10_sp0p35_exp_2s">Expected +- 2 sigma 95% CL exclusion limit for bbA production in the 2HDM+a model</a> <li><a href="?table=LimitContour_ZP2HDM_2018CONF_obs">Observed 95% CL exclusion limit for the Z'-2HDM model with the benchmark used in arXiv:1707.01302.</a> <li><a href="?table=LimitContour_ZP2HDM_2018CONF_exp">Expected 95% CL exclusion limit for the Z'-2HDM model with the benchmark used in arXiv:1707.01302.</a> <li><a href="?table=LimitContour_ZP2HDM_2018CONF_exp_1s">Expected +- 1 sigma 95% CL exclusion limit for the Z'-2HDM model with the benchmark used in arXiv:1707.01302.</a> <li><a href="?table=LimitContour_ZP2HDM_2018CONF_exp_2s">Expected +- 2 sigma 95% CL exclusion limit for the Z'-2HDM model with the benchmark used in arXiv:1707.01302.</a> </ul> <b>Upper limits on cross-sections:</b> <ul> <li><a href="?table=Limits_ZP2HDM">95% CL upper limit on the cross-section for the Z'-2HDM model</a> <li><a href="?table=Limits_2HDMa_tb1_sp0p35">95% CL upper limit on the ggF cross-section in the 2HDM+a model</a> <li><a href="?table=Limits_2HDMa_tb10_sp0p35">95% CL upper limit on the bbA cross-section in the 2HDM+a model</a> <li><a href="?table=MIL">95% CL upper limit on the visible cross-section</a> </ul> <b>Theoretical cross-sections:</b> <ul> <li><a href="?table=CrossSections_ZP2HDM">Cross-section for the Z'-2HDM model</a> <li><a href="?table=CrossSections_2HDMa_tb1_sp0p35">Cross-section for ggF production in the 2HDM+a model</a> <li><a href="?table=CrossSections_2HDMa_tb10_sp0p35">Cross-section for bbA production in the 2HDM+a model</a> </ul> <b>Kinematic distributions:</b> <ul> <li><a href="?table=SR_post_plot_2b_150_200">Higgs candidate invariant mass in the region with 2 b-jets and missing energy between 150-200 GeV</a> <li><a href="?table=SR_post_plot_2b_200_350">Higgs candidate invariant mass in the region with 2 b-jets and missing energy between 200-350 GeV</a> <li><a href="?table=SR_post_plot_2b_350_500">Higgs candidate invariant mass in the region with 2 b-jets and missing energy between 350-500 GeV</a> <li><a href="?table=SR_post_plot_2b_500_750">Higgs candidate invariant mass in the region with 2 b-jets and missing energy between 500-750 GeV</a> <li><a href="?table=SR_post_plot_2b_750">Higgs candidate invariant mass in the region with 2 b-jets and missing energy higher than 750 GeV</a> <li><a href="?table=SR_post_plot_3b_150_200">Higgs candidate invariant mass in the region with at least 3 b-jets and missing energy between 150-200 GeV</a> <li><a href="?table=SR_post_plot_3b_200_350">Higgs candidate invariant mass in the region with at least 3 b-jets and missing energy between 200-350 GeV</a> <li><a href="?table=SR_post_plot_3b_350_500">Higgs candidate invariant mass in the region with at least 3 b-jets and missing energy between 350-500 GeV</a> <li><a href="?table=SR_post_plot_3b_500">Higgs candidate invariant mass in the region with at least 3 b-jets and missing energy higher than 500 GeV</a> <li><a href="?table=MET_post_plot_0L2b">Missing energy in events with 0 leptons and 2 b-jets</a> <li><a href="?table=MET_post_plot_0L3b">Missing energy in events with 0 leptons and at least 3 b-jets</a> <li><a href="?table=CR_post_plot_CR1">Yields in the different missing energy bins and muon-charge of the 1-lepton control region</a> <li><a href="?table=CR_post_plot_CR2">Yields in the different METlepInv bins of the 2-lepton control region</a> </ul> <b>Cut flows:</b> The tables contain three columns, corresponding to the Z'-2HDM and 2HDM+a model assuming 100% ggF or bbA production respectively. <ul> <li><a href="?table=Resolved_150_200_2b">Signal region with 2 b-jets and missing energy between 150-200 GeV</a> <li><a href="?table=Resolved_200_350_2b">Signal region with 2 b-jets and missing energy between 200-350 GeV</a> <li><a href="?table=Resolved_350_500_2b">Signal region with 2 b-jets and missing energy between 350-500 GeV</a> <li><a href="?table=Merged_500_750_2w0b">Signal region with 2 b-jets and missing energy between 500-750 GeV</a> <li><a href="?table=Merged_750_2w0b">Signal region with 2 b-jets and missing energy higher than 750 GeV</a> <li><a href="?table=Resolved_150_200_3pb">Signal region with at least 3 b-jets and missing energy between 150-200 GeV</a> <li><a href="?table=Resolved_200_350_3pb">Signal region with at least 3 b-jets and missing energy between 200-350 GeV</a> <li><a href="?table=Resolved_350_500_3pb">Signal region with at least 3 b-jets and missing energy between 350-500 GeV</a> <li><a href="?table=Merged_2w1pb">Signal region with at least 3 b-jets and missing energy higher than 500 GeV</a> </ul> <b>Acceptance and efficiencies:</b> <ul> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_bb_2_150_noHiggsWindowCut">2HDM+a model, bbA production, 2 b-jets, MET=150-200 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_bb_2_200_noHiggsWindowCut">2HDM+a model, bbA production, 2 b-jets, MET=200-350 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_bb_2_350_noHiggsWindowCut">2HDM+a model, bbA production, 2 b-jets, MET=350-500 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_bb_2_500_noHiggsWindowCut">2HDM+a model, bbA production, 2 b-jets, MET=500-750 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_bb_2_750ptv_noHiggsWindowCut">2HDM+a model, bbA production, 2 b-jets, MET higher than 750 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_bb_3_150_noHiggsWindowCut">2HDM+a model, bbA production, at least 3 b-jets, MET=150-200 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_bb_3_200_noHiggsWindowCut">2HDM+a model, bbA production, at least 3 b-jets, MET=200-350 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_bb_3_350_noHiggsWindowCut">2HDM+a model, bbA production, at least 3 b-jets, MET=350-500 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_bb_3_500ptv_noHiggsWindowCut">2HDM+a model, bbA production, at least 3 b-jets, MET higher than GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_ggF_2_150_noHiggsWindowCut">2HDM+a model, ggF production, 2 b-jets, MET=150-200 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_ggF_2_200_noHiggsWindowCut">2HDM+a model, ggF production, 2 b-jets, MET=200-350 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_ggF_2_350_noHiggsWindowCut">2HDM+a model, ggF production, 2 b-jets, MET=350-500 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_ggF_2_500_noHiggsWindowCut">2HDM+a model, ggF production, 2 b-jets, MET=500-750 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_ggF_2_750ptv_noHiggsWindowCut">2HDM+a model, ggF production, 2 b-jets, MET higher than 750 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_ggF_3_150_noHiggsWindowCut">2HDM+a model, ggF production, at least 3 b-jets, MET=150-200 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_ggF_3_200_noHiggsWindowCut">2HDM+a model, ggF production, at least 3 b-jets, MET=200-350 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_ggF_3_350_noHiggsWindowCut">2HDM+a model, ggF production, at least 3 b-jets, MET=350-500 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_a2HDM_ggF_3_500ptv_noHiggsWindowCut">2HDM+a model, ggF production, at least 3 b-jets, MET higher than 500 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_zp2hdm_CMS_2_150_noHiggsWindowCut">Z'-2HDM model, 2 b-jets, MET=150-200 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_zp2hdm_CMS_2_200_noHiggsWindowCut">Z'-2HDM model, 2 b-jets, MET=200-350 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_zp2hdm_CMS_2_350_noHiggsWindowCut">Z'-2HDM model, 2 b-jets, MET=350-500 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_zp2hdm_CMS_2_500_noHiggsWindowCut">Z'-2HDM model, 2 b-jets, MET=500-750 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_zp2hdm_CMS_2_750ptv_noHiggsWindowCut">Z'-2HDM model, 2 b-jets, MET higher than 750 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_zp2hdm_CMS_3_150_noHiggsWindowCut">Z'-2HDM model, at least 3 b-jets, MET=150-200 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_zp2hdm_CMS_3_200_noHiggsWindowCut">Z'-2HDM model, at least 3 b-jets, MET=200-350 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_zp2hdm_CMS_3_350_noHiggsWindowCut">Z'-2HDM model, at least 3 b-jets, MET=350-500 GeV</a> <li><a href="?table=AcceptanceTimesEfficiency_zp2hdm_CMS_3_500ptv_noHiggsWindowCut">Z'-2HDM model, at least 3 b-jets, MET higher than 500 GeV</a> </ul>
Observed 95% CL exclusion limit for the Zprime-2HDM model.
Expected 95% CL exclusion limit for the Zprime-2HDM model.
A search for diphoton resonances in the mass range between 10 and 70 GeV with the ATLAS experiment at the Large Hadron Collider (LHC) is presented. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 138 fb$^{-1}$ at a centre-of-mass energy of 13 TeV recorded from 2015 to 2018. Previous searches for diphoton resonances at the LHC have explored masses down to 65 GeV, finding no evidence of new particles. This search exploits the particular kinematics of events with pairs of closely spaced photons reconstructed in the detector, allowing examination of invariant masses down to 10 GeV. The presented strategy covers a region previously unexplored at hadron colliders because of the experimental challenges of recording low-energy photons and estimating the backgrounds. No significant excess is observed and the reported limits provide the strongest bound on promptly decaying axion-like particles coupling to gluons and photons for masses between 10 and 70 GeV.
The expected and observed upper limits at 95\% CL on the fiducial cross-section times branching ratio to two photons of a narrow-width ($\Gamma_{X}$ = 4 MeV) scalar resonance as a function of its mass $m_{X}$.
Diphoton invariant mass in the signal region using a 0.1 GeV binning.
Parametrization of the $C_{X}$ factor, defined as the ratio between the number of reconstructed signal events passing the analysis cuts and the number of signal events at the particle level generated within the fiducial volume, as function of $m_{X}$ obtained from the narrow width simulated signal samples produced in gluon fusion.
Cross-sections for the production of a $Z$ boson in association with two photons are measured in proton$-$proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 139 fb$^{-1}$ recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the $Z$ boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated $Z(\rightarrow\ell\ell)\gamma\gamma$ cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the $Z\gamma\gamma$ 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.
Measured fiducial-level integrated cross-section. NLO predictions from Sherpa 2.2.10 and MadGraph5_aMC@NLO 2.7.3 are also shown. The uncertainty in the predictions is divided into statistical and theoretical uncertainties (scale and PDF+$\alpha_{s}$).
Measured unfolded differential cross-section as a function of the leading photon transverse energy $E^{\gamma1}_{\mathrm{T}}$. NLO predictions from Sherpa 2.2.10 and MadGraph5_aMC@NLO 2.7.3 are also shown. The uncertainty in the predictions is divided into statistical and theoretical uncertainties (scale and PDF+$\alpha_{s}$).
Measured unfolded differential cross-section as a function of the subleading photon transverse energy $E^{\gamma2}_{\mathrm{T}}$. NLO predictions from Sherpa 2.2.10 and MadGraph5_aMC@NLO 2.7.3 are also shown. The uncertainty in the predictions is divided into statistical and theoretical uncertainties (scale and PDF+$\alpha_{s}$).
A search for Higgs boson pair production in events with two $b$-jets and two $\tau$-leptons is presented, using a proton-proton collision dataset with an integrated luminosity of 139 fb$^{-1}$ collected at $\sqrt{s}=13$ TeV by the ATLAS experiment at the LHC. Higgs boson pairs produced non-resonantly or in the decay of a narrow scalar resonance in the mass range from 251 to 1600 GeV are targeted. Events in which at least one $\tau$-lepton decays hadronically are considered, and multivariate discriminants are used to reject the backgrounds. No significant excess of events above the expected background is observed in the non-resonant search. The largest excess in the resonant search is observed at a resonance mass of 1 TeV, with a local (global) significance of $3.1\sigma$ ($2.0\sigma$). Observed (expected) 95% confidence-level upper limits are set on the non-resonant Higgs boson pair-production cross-section at 4.7 (3.9) times the Standard Model prediction, assuming Standard Model kinematics, and on the resonant Higgs boson pair-production cross-section at between 21 and 900 fb (12 and 840 fb), depending on the mass of the narrow scalar resonance.
Breakdown of the relative contributions to the uncertainty in the extracted signal cross-sections, as determined in the likelihood fit (described in Section 8) to data. These are obtained by fixing the relevant nuisance parameters in the likelihood fit, and subtracting the obtained uncertainty on the fitted signal cross-sections in quadrature from the total uncertainty, and then dividing the result by the total uncertainty. The sum in quadrature of the individual components differs from the total uncertainty due to correlations between uncertainties in the different groups.
Post-fit expected number of signal and background events and observed number of data events in the last two bins of the non-resonant BDT score distribution of the SM signal after applying the selection criteria and requiring exactly 2 b-tagged jets and assuming a background-only hypothesis
Observed and expected upper limits at 95% CL on the cross-section of non-resonant HH production according to SM-like kinematics, and on the cross-section of non-resonant HH production divided by the SM prediction. The 1 sigma and 2 sigma variations around the expected limit are also shown.
Searches are performed for nonresonant and resonant di-Higgs boson production in the $b\bar{b}\gamma\gamma$ final state. The data set used corresponds to an integrated luminosity of 139 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No excess above the expected background is found and upper limits on the di-Higgs boson production cross sections are set. A 95% confidence-level upper limit of 4.2 times the cross section predicted by the Standard Model is set on $pp \rightarrow HH$ nonresonant production, where the expected limit is 5.7 times the Standard Model predicted value. The expected constraints are obtained for a background hypothesis excluding $pp \rightarrow HH$ production. The observed (expected) constraints on the Higgs boson trilinear coupling modifier $\kappa_{\lambda}$ are determined to be $[-1.5, 6.7]$ $([-2.4, 7.7])$ at 95% confidence level, where the expected constraints on $\kappa_{\lambda}$ are obtained excluding $pp \rightarrow HH$ production from the background hypothesis. For resonant production of a new hypothetical scalar particle $X$ ($X \rightarrow HH \rightarrow b\bar{b}\gamma\gamma$), limits on the cross section for $pp \to X \to HH$ are presented in the narrow-width approximation as a function of $m_{X}$ in the range $251 \leq m_{X} \leq 1000$ GeV. The observed (expected) limits on the cross section for $pp \to X \to HH$ range from 640 fb to 44 fb (391 fb to 46 fb) over the considered mass range.
The BDT distribution of the di-Higgs ggF signal for two different values of $\kappa_{\lambda}$ and the main backgrounds in the low mass region ($m^{*}_{b\bar{b}\gamma\gamma} < 350$ GeV). Distributions are normalized to unit area. The dotted lines denote the category boundaries. Events with a BDT score below 0.881 in the low mass region are discarded.
The BDT distribution (with x-axis zoomed in) of the di-Higgs ggF signal for two different values of $\kappa_{\lambda}$ and the main backgrounds in the low mass region ($m^{*}_{b\bar{b}\gamma\gamma} < 350$ GeV). Distributions are normalized to unit area. The dotted lines denote the category boundaries. Events with a BDT score below 0.881 in the low mass region are discarded. The range of BDT scores is from 0.8 to 1.
The BDT distribution of the di-Higgs ggF signal for two different values of $\kappa_{\lambda}$ and the main backgrounds in the high mass region ($m^{*}_{b\bar{b}\gamma\gamma} > 350$ GeV). Distributions are normalized to unit area. The dotted lines denote the category boundaries. Events with a BDT score below 0.857 in the high mass region are discarded.
This paper presents a statistical combination of searches targeting final states with two top quarks and invisible particles, characterised by the presence of zero, one or two leptons, at least one jet originating from a $b$-quark and missing transverse momentum. The analyses are searches for phenomena beyond the Standard Model consistent with the direct production of dark matter in $pp$ collisions at the LHC, using 139 fb$^{-\text{1}}$ of data collected with the ATLAS detector at a centre-of-mass energy of 13 TeV. The results are interpreted in terms of simplified dark matter models with a spin-0 scalar or pseudoscalar mediator particle. In addition, the results are interpreted in terms of upper limits on the Higgs boson invisible branching ratio, where the Higgs boson is produced according to the Standard Model in association with a pair of top quarks. For scalar (pseudoscalar) dark matter models, with all couplings set to unity, the statistical combination extends the mass range excluded by the best of the individual channels by 50 (25) GeV, excluding mediator masses up to 370 GeV. In addition, the statistical combination improves the expected coupling exclusion reach by 14% (24%), assuming a scalar (pseudoscalar) mediator mass of 10 GeV. An upper limit on the Higgs boson invisible branching ratio of 0.38 (0.30$^{+\text{0.13}}_{-\text{0.09}}$) is observed (expected) at 95% confidence level.
Post-fit signal region yields for the tt0L-high and the tt0L-low analyses. The bottom panel shows the statistical significance of the difference between the SM prediction and the observed data in each region. '$t\bar{t}$ (other)' represents $t\bar{t}$ events without extra jets or events with extra light-flavour jets. 'Other' includes contributions from $t\bar{t}W$, $tZ$ and $tWZ$ processes. The total uncertainty in the SM expectation is represented with hatched bands and the expected distributions for selected signal models are shown as dashed lines.
Representative fit distribution in the signal region for the tt1L analysis: each bin of such distribution corresponds to a single SR included in the fit. 'Other' includes contributions from $t\bar{t}W$, $tZ$, $tWZ$ and $t\bar{t}$ (semileptonic) processes. The total uncertainty in the SM expectation is represented with hatched bands and the expected distributions for selected signal models are shown as dashed lines.
Representative fit distribution in the same flavour leptons signal region for the tt2L analysis: each bin of such distribution, starting from the red arrow, corresponds to a single SR included in the fit. 'FNP' includes the contribution from fake/non-prompt lepton background arising from jets (mainly $\pi/K$, heavy-flavour hadron decays and photon conversion) misidentified as leptons, estimated in a purely data-driven way. 'Other' includes contributions from $t\bar{t}W$, $tZ$ and $tWZ$ processes. The total uncertainty in the SM expectation is represented with hatched bands and the expected distributions for selected signal models are shown as dashed lines.
The associated production of a Higgs boson and a top-quark pair is measured in events characterised by the presence of one or two electrons or muons. The Higgs boson decay into a $b$-quark pair is used. The analysed data, corresponding to an integrated luminosity of 139 fb$^{-1}$, were collected in proton-proton collisions at the Large Hadron Collider between 2015 and 2018 at a centre-of-mass energy of $\sqrt{s}=13$ TeV. The measured signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model, is $0.35^{+0.36}_{-0.34}$. This result is compatible with the Standard Model prediction and corresponds to an observed (expected) significance of 1.0 (2.7) standard deviations. The signal strength is also measured differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, including a bin for specially selected boosted Higgs bosons with transverse momentum above 300 GeV.
Comparison between data and prediction for the DNN $P(H)$ output for the Higgs boson candidate prior to any fit to the data in the single-lepton boosted channel for $300\le p_T^H<450$ GeV. The dashed line shows the ${t\bar {t}H}$ signal distribution normalised to the total background prediction. The uncertainty band includes all uncertainties and their correlations.
Comparison between data and prediction for the DNN $P(H)$ output for the Higgs boson candidate prior to any fit to the data in the single-lepton boosted channel for $p_{{T}}^{H}\ge 450$ GeV. The dashed line shows the ${t\bar {t}H}$ signal distribution normalised to the total background prediction. The uncertainty band includes all uncertainties and their correlations.
Performance of the Higgs boson reconstruction algorithms. For each row of `truth' ${\hat{p}_{{T}}^{H}}$, the matrix shows (in percentages) the fraction of all Higgs boson candidates with reconstructed $p_T^H$ in the various bins of the dilepton (left), single-lepton resolved (middle) and boosted (right) channels.