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Search for a new scalar decaying into new spin-1 bosons in four-lepton final states with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abeling, Kira ; et al.
Phys.Lett.B 865 (2025) 139472, 2025.
Inspire Record 2842018 DOI 10.17182/hepdata.145171

A search is conducted for a new scalar boson $S$, with a mass distinct from that of the Higgs boson, decaying into four leptons ($\ell =$$e$, $\mu$) via an intermediate state containing two on-shell, promptly decaying new spin-1 bosons $Z_\text{d}$: $S \rightarrow Z_\text{d}Z_\text{d} \rightarrow 4\ell$, where the $Z_\text{d}$ boson has a mass between 15 and 300 GeV, and the $S$ boson has a mass between either 30 and 115 GeV or 130 and 800 GeV. The search uses proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider with an integrated luminosity of 139 fb$^{-1}$ at a centre-of-mass energy of $\sqrt{s}=13$ TeV. No significant excess above the Standard Model background expectation is observed. Upper limits at 95% confidence level are set on the production cross-section times branching ratio, $\sigma(gg \to S) \times \mathcal{B}(S\rightarrow Z_\text{d}Z_\text{d} \rightarrow 4\ell)$, as a function of the mass of both particles, $m_S$ and $m_{Z\text{d}}$.

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Average dilepton mass distribution $\left\langle m_{\ell\ell}\right\rangle = \frac{1}{2}\left(m_{ab} + m_{cd}\right)$ in Signal Region 1.

Average dilepton mass distribution $\left\langle m_{\ell\ell}\right\rangle = \frac{1}{2}\left(m_{ab} + m_{cd}\right)$ in Signal Region 2.

Total invariant mass distribution $m_{4\ell}$ in Signal Region 1.

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Search for heavy resonances decaying into a pair of $Z$ bosons in the $\ell^+\ell^-\ell'^+\ell'^-$ and $\ell^+\ell^-\nu\bar\nu$ final states using 139 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, Brad ; et al.
Eur.Phys.J.C 81 (2021) 332, 2021.
Inspire Record 1820316 DOI 10.17182/hepdata.97159

A search for heavy resonances decaying into a pair of $Z$ bosons leading to $\ell^+\ell^-\ell'^+\ell'^-$ and $\ell^+\ell^-\nu\bar\nu$ final states, where $\ell$ stands for either an electron or a muon, is presented. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV collected from 2015 to 2018 that corresponds to the full integrated luminosity of 139 fb$^{-1}$ recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. Different mass ranges spanning 200 GeV to 2000 GeV for the hypothetical resonances are considered, depending on the final state and model. In the absence of a significant observed excess, the results are interpreted as upper limits on the production cross section of a spin-0 or spin-2 resonance. The upper limits for the spin-0 resonance are translated to exclusion contours in the context of Type-I and Type-II two-Higgs-doublet models, and the limits for the spin-2 resonance are used to constrain the Randall--Sundrum model with an extra dimension giving rise to spin-2 graviton excitations.

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Distribution of the four-lepton invariant mass in the four-lepton final state for the ggF-MVA-high 4-muon category.

Distribution of the four-lepton invariant mass in the four-lepton final state for the ggF-MVA-high 2e2mu category.

Distribution of the four-lepton invariant mass in the four-lepton final state for the ggF-MVA-high 4-electron category.

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Search for Higgs boson production in association with a high-energy photon via vector-boson fusion with decay into bottom quark pairs at $\sqrt{s}$=13 TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, Brad ; et al.
JHEP 03 (2021) 268, 2021.
Inspire Record 1826521 DOI 10.17182/hepdata.100160

A search is presented for the production of the Standard Model Higgs boson in association with a high-energy photon. With a focus on the vector-boson fusion process and the dominant Higgs boson decay into $b$-quark pairs, the search benefits from a large reduction of multijet background compared to more inclusive searches. Results are reported from the analysis of 132 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$=13 TeV collected with the ATLAS detector at the LHC. The measured Higgs boson signal yield in this final-state signature is $1.3 \pm 1.0$ times the Standard Model prediction. The observed significance of the Higgs boson signal above the background is 1.3 standard deviations, compared to an expected significance of 1.0 standard deviations.

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Comparisons of data and simulated event distributions of the BDT input variable \(\Delta \eta_{jj}\) in the two \(m_{bb}\) sidebands after kinematic reweighting of the non-resonant \(b\bar{b}\gamma jj\) background. The data are shown as black points, and the background contributions are stacked in coloured histograms. The Higgs boson signal contribution is scaled up and represented by the dashed red line. The bottom panel in each plot shows the ratio of the data to the SM prediction, where the uncertainty band corresponds to the statistical uncertainty only.

Comparisons of data and simulated event distributions of the BDT input variable \(p_{\text{T}}^{\text{balance}}\) in the two \(m_{bb}\) sidebands after kinematic reweighting of the non-resonant \(b\bar{b}\gamma jj\) background. The data are shown as black points, and the background contributions are stacked in coloured histograms. The Higgs boson signal contribution is scaled up and represented by the dashed red line. The bottom panel in each plot shows the ratio of the data to the SM prediction, where the uncertainty band corresponds to the statistical uncertainty only.

The \(m_{bb}\) distributions in the HighBDT categories, overlaid with contributions from the \(H\gamma jj\) signal as well as the resonant \(Z\gamma jj\) and non-resonant \(b\bar{b} \gamma jj\) background fits. The combined \(\chi^2\) per degree of freedom is \(45.2/45\). The bottom panel in each plot presents the significance of the Higgs boson signal relative to the non-resonant \(b\bar{b} \gamma jj\) background in each bin.

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Version 2
Search for trilepton resonances from chargino and neutralino pair production in $\sqrt{s}$ = 13 TeV $pp$ collisions with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, Brad ; et al.
Phys.Rev.D 103 (2021) 112003, 2021.
Inspire Record 1831992 DOI 10.17182/hepdata.99806

A search is performed for the electroweak pair production of charginos and associated production of a chargino and neutralino, each of which decays through an $R$-parity-violating coupling into a lepton and a $W$, $Z$, or Higgs boson. The trilepton invariant-mass spectrum is constructed from events with three or more leptons, targeting chargino decays that include an electron or muon and a leptonically decaying $Z$ boson. The analyzed dataset corresponds to an integrated luminosity of 139 fb$^{-1}$ of proton-proton collision data produced by the Large Hadron Collider at a center-of-mass energy of $\sqrt{s}$ = 13 TeV and collected by the ATLAS experiment between 2015 and 2018. The data are found to be consistent with predictions from the Standard Model. The results are interpreted as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model. Limits are also set on the production of charginos and neutralinos for a Minimal Supersymmetric Standard Model with an approximate $B$-$L$ symmetry. Charginos and neutralinos with masses between 100 GeV and 1100 GeV are excluded depending on the assumed decay branching fractions into a lepton (electron, muon, or $\tau$-lepton) plus a boson ($W$, $Z$, or Higgs).

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The observed data and the SM background expectation in the CRs (pre-fit) and VRs (post-fit). The ''Other'' category mostly consists of tW Z, ttW, and tZ processes. The hatched bands indicate the combined theoretical, experimental, and MC statistical uncertainties. The bottom panel shows the fractional difference between the observed data and expected yields for the CRs and the significance of the difference for the VRs, computed following the profile likelihood method described in Ref. [arXiv: physics/0702156].

The observed yields and post-fit background expectations in SRFR, SR4$\ell$, and SR3$\ell$, shown inclusively and when the direct lepton from a $\tilde\chi^{\pm}_{1}/\tilde\chi^{0}_{1}$ decay is required to be an electron or muon. The Other category mostly consists of $tWZ$, $t\bar{t}W$, and $tZ$ processes. Uncertainties on the background expectation include combined statistical and systematic uncertainties. The individual uncertainties may be correlated and do not necessarily add in quadrature to equal the total background uncertainty.

The observed data and post-fit SM background expectation as a function of $m_{Z\ell}$ in SRFR. The $m_{Z\ell}$ binning is the same as used in the fit and the yield is normalized to the bin width, with the last bin normalized using a width of 200 GeV. the "Other" category mostly consists of $tWZ$, $t\bar{t}W$, and $tZ$ processes. The hatched bands indicate the combined theoretical, experimental, and MC statistical uncertainties. The bottom panel shows the significance of the differences between the observed data and expected yields, computed following the profile likelihood method described in ref.[arxiv: physics/0702156]

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Constraints on Higgs boson production with large transverse momentum using $H\rightarrow b\bar{b}$ decays in the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, Dale ; et al.
Phys.Rev.D 105 (2022) 092003, 2022.
Inspire Record 1969589 DOI 10.17182/hepdata.102183

This paper reports constraints on Higgs boson production with transverse momentum above 1 TeV. The analyzed data from proton-proton collisions at a center-of-mass energy of 13 TeV were recorded with the ATLAS detector at the Large Hadron Collider from 2015 to 2018 and correspond to an integrated luminosity of 136 fb$^{-1}$. Higgs bosons decaying into $b\bar{b}$ are reconstructed as single large-radius jets recoiling against a hadronic system and identified by the experimental signature of two $b$-hadron decays. The experimental techniques are validated in the same kinematic regime using the $Z\rightarrow b\bar{b}$ process.The 95$\% $ confidence-level upper limit on the cross section for Higgs boson production with transverse momentum above 450 GeV is 115 fb, and above 1 TeV it is 9.6 fb. The Standard Model cross section predictions for a Higgs boson with a mass of 125 GeV in the same kinematic regions are 18.4 fb and 0.13 fb, respectively.

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Predicted Higgs boson production cross sections within fiducial volumes obtained from the four production mode MC samples (ggF, VBF, VH, and ttH) described in Section 3 with and without higher order electroweak (EW) corrections. All μH values reported are with respect to cross section with EW corrections.

The efficiency for simulated ggF events to pass each analysis cut.

The efficiency for simulated VBF events to pass each analysis cut.

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Evidence for Higgs boson decays to a low-mass dilepton system and a photon in pp collisions at $\sqrt{s} =$ 13 TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, Dale Charles ; et al.
Phys.Lett.B 819 (2021) 136412, 2021.
Inspire Record 1852325 DOI 10.17182/hepdata.102955

A search for the Higgs boson decaying into a photon and a pair of electrons or muons with an invariant mass $m_{\ell\ell} < 30$ GeV is presented. The analysis is performed using 139 fb$^{-1}$ of proton-proton collision data, produced by the LHC at a centre-of-mass energy of 13 TeV and collected by the ATLAS experiment. Evidence for the $H \rightarrow \ell \ell \gamma$ process is found with a significance of 3.2$\sigma$ over the background-only hypothesis, compared to an expected significance of 2.1$\sigma$. The best-fit value of the signal strength parameter, defined as the ratio of the observed signal yield to the one expected in the Standard Model, is $\mu = 1.5 \pm 0.5$. The Higgs boson production cross-section times the $H \rightarrow\ell\ell\gamma$ branching ratio for $m_{\ell\ell} <$ 30 GeV is determined to be 8.7 $^{+2.8}_{-2.7}$ fb.

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The best fit value for the signal yield normalised to the Standard Model prediction (signal strength) for $pp \to H \to Z+\gamma$

Measured $\sigma( p p \rightarrow H) \cdot B(H\rightarrow \ell\ell\gamma)$ for $m_{\ell\ell} < 30$ GeV


A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, Dale ; et al.
Nature 607 (2022) 52-59, 2022.
Inspire Record 2104706 DOI 10.17182/hepdata.130266

The Standard Model of particle physics describes the known fundamental particles and forces that make up our universe, with the exception of gravity. One of the central features of the Standard Model is a field that permeates all of space and interacts with fundamental particles. The quantum excitation of this field, known as Higgs field, manifests itself as the Higgs boson, the only fundamental particle with no spin. In 2012, a particle with properties consistent with the Higgs boson of the Standard Model was observed by the ATLAS and CMS experiments at the Large Hadron Collider at CERN. Since then, more than 30 times as many Higgs bosons have been recorded by the ATLAS experiment, allowing much more precise measurements and new tests of the theory. Here, on the basis of this larger dataset, we combine an unprecedented number of production and decay processes of the Higgs boson to scrutinize its interactions with elementary particles. Interactions with gluons, photons, and $W$ and $Z$ bosons -- the carriers of the strong, electromagnetic, and weak forces -- are studied in detail. Interactions with three third-generation matter particles (bottom ($b$) and top ($t$) quarks, and tau leptons ($\tau$)) are well measured and indications of interactions with a second-generation particle (muons, $\mu$) are emerging. These tests reveal that the Higgs boson discovered ten years ago is remarkably consistent with the predictions of the theory and provide stringent constraints on many models of new phenomena beyond the Standard Model.

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Observed and predicted branching fractions for different Higgs boson decay modes measured assuming SM values for the production cross sections. The lower panels show the ratios of the measured values to their SM predictions. The $p$-value for compatibility of the measurement and the SM prediction is 56%.


Version 4
Search for Higgs boson pair production in the two bottom quarks plus two photons final state in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, Dale ; et al.
Phys.Rev.D 106 (2022) 052001, 2022.
Inspire Record 1995886 DOI 10.17182/hepdata.105864

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.

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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.

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Strong constraints on jet quenching in centrality-dependent $p$+Pb collisions at 5.02 TeV from ATLAS

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, D.C. ; et al.
Phys.Rev.Lett. 131 (2023) 072301, 2023.
Inspire Record 2090791 DOI 10.17182/hepdata.130943

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 $pp$ 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 $pp$ collisions at 5.02 TeV. The yields of charged hadrons with $p_\mathrm{T}^\mathrm{ch} >0.5$ GeV near and opposite in azimuth to jets with $p_\mathrm{T}^\mathrm{jet} > 30$ or $60$ GeV, and the ratios of these yields between $p$+Pb and $pp$ collisions, $I_{p\mathrm{Pb}}$, are reported. The collision centrality of $p$+Pb events is categorized by the energy deposited by forward neutrons from the struck nucleus. The $I_{p\mathrm{Pb}}$ values are consistent with unity within a few percent for hadrons with $p_\mathrm{T}^\mathrm{ch} >4$ GeV at all centralities. These data provide new, strong constraints which preclude almost any parton energy loss in central $p$+Pb collisions.

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The per-jet charged particle yield in pPb and pp collisions for hadrons near a $p_{T}^{\textrm{jet}} > 30~\textrm{GeV}$ jet ($\Delta\phi_{\textrm{ch,jet}} < \pi/8$).

The per-jet charged particle yield in pPb and pp collisions for hadrons opposite to a $p_{T}^{\textrm{jet}} > 30~\textrm{GeV}$ jet ($\Delta\phi_{\textrm{ch,jet}} > 7\pi/8$).

The per-jet charged particle yield in pPb and pp collisions for hadrons near a $p_{T}^{\textrm{jet}} > 60~\textrm{GeV}$ jet ($\Delta\phi_{\textrm{ch,jet}} < \pi/8$).

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Search for flavour-changing neutral-current couplings between the top quark and the photon with the ATLAS detector at $\sqrt{s} = 13$ TeV

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, Dale ; et al.
Phys.Lett.B 842 (2023) 137379, 2023.
Inspire Record 2077557 DOI 10.17182/hepdata.129959

This letter documents a search for flavour-changing neutral currents (FCNCs), which are strongly suppressed in the Standard Model, in events with a photon and a top quark with the ATLAS detector. The analysis uses data collected in $pp$ collisions at $\sqrt{s} = 13$ TeV during Run 2 of the LHC, corresponding to an integrated luminosity of 139 fb$^{-1}$. Both FCNC top-quark production and decay are considered. The final state consists of a charged lepton, missing transverse momentum, a $b$-tagged jet, one high-momentum photon and possibly additional jets. A multiclass deep neural network is used to classify events either as signal in one of the two categories, FCNC production or decay, or as background. No significant excess of events over the background prediction is observed and 95% CL upper limits are placed on the strength of left- and right-handed FCNC interactions. The 95% CL bounds on the branching fractions for the FCNC top-quark decays, estimated from both top-quark production and decay, are $\mathcal{B}(t\rightarrow u\gamma) < 0.85 \times 10^{-5}$ and $\mathcal{B}(t\to c\gamma) < 4.2 \times 10^{-5}$ for a left-handed $tq\gamma$ coupling, and $\mathcal{B}(t\to u\gamma) < 1.2 \times 10^{-5}$ and $\mathcal{B}(t\to c\gamma) < 4.5 \times 10^{-5}$ for a right-handed coupling.

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Post-fit distribution of a background-only fit to the NN discriminant in the SR for the $tu\gamma$ coupling. The last bin of the distribution contains the overflow and the first bin also contains the underflow. In addition, the expected $tu\gamma$ LH signal is overlaid for an expected number of events corresponding to the observed 95% CL limit scaled by a factor of ten. The uncertainty band includes both the statistical and systematic uncertainties in the background prediction as well as the correlations of the uncertainties as obtained by the fit.

Post-fit distribution of a background-only fit to the photon transverse momentum distribution in the $t\bar{t}\gamma$ CR. The last bin of the distribution contains the overflow. The uncertainty band includes both the statistical and systematic uncertainties in the background prediction as well as the correlations of the uncertainties as obtained by the fit.

Post-fit distribution of a background-only fit to the photon transverse momentum distribution in the $W\gamma$+jets CR. The last bin of the distribution contains the overflow. The uncertainty band includes both the statistical and systematic uncertainties in the background prediction as well as the correlations of the uncertainties as obtained by the fit.

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