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| CMS-EXO-24-008 ; CERN-EP-2025-241 | ||
| Search for low-mass hidden-valley dark showers with non-prompt muon pairs in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 14 November 2025 | ||
| Submitted to J. High Energy Phys. | ||
| Abstract: A search for signatures of a dark analog to quantum chromodynamics is performed. The analysis targets long-lived dark mesons that decay into standard-model particles, with a high branching fraction of the dark mesons decaying into muons. The dark mesons are formed by the hadronisation of dark partons, which are produced by a decay of the Higgs boson. The search is performed using a data set corresponding to an integrated luminosity of 41.6 fb$ ^{-1} $, which was collected in proton-proton collisions at $ \sqrt{s}= $ 13 TeV by the CMS experiment at the CERN LHC in 2018 using non-prompt muon triggers. The search is based on resonant muon pair signatures. Machine-learning techniques are employed in the analysis, utilising boosted decision trees to discriminate between signal and background. No significant excess is observed above the standard model expectation. Upper limits on the branching fraction of the Higgs boson decaying to dark partons are determined to be as low as $ 10^{-4} $ at 95% confidence level, surpassing and extending the existing limits on models with dark $ \tilde{\omega} $ mesons for mean proper decay lengths of less than 500 mm and for $ \tilde{\omega} $ masses down to 0.3 GeV. First limits are set for extended dark-shower models with two dark flavours that contain dark photons, probing their masses down to 0.33 GeV. | ||
| Links: e-print arXiv:2511.11888 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Diagram for the vector portal model. An SM Higgs boson decays to dark partons $ \psi\bar{\psi} $, which then hadronise to form dark hadrons including dark vector mesons $ \tilde{\omega} $ and dark pseudoscalar mesons $ \tilde{\eta} $. The $ \tilde{\omega} $ then undergoes displaced decay into SM fermions $ f\bar{f} $. |
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Figure 2:
Diagrams for the Scenario A model (left) and the Scenario B1 model (right). In these extended models the dark hadronisation produces a spectrum of dark mesons, including the dark pions $ \tilde{\pi}_{1} $, $ \tilde{\pi}_{2} $ and $ \tilde{\pi}_{3} $. The $ \tilde{\pi}_{3} $ then decays into SM fermions $ f\bar{f} $ through the dark photon $ \mathrm{A}' $. Green is used to indicate a long-lived particle. The $ \mathrm{A}' $ is a long-lived particle in Scenario A, while $ \tilde{\pi}_{3} $ is a long-lived particle in Scenario B1. |
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Figure 2-a:
Diagrams for the Scenario A model (left) and the Scenario B1 model (right). In these extended models the dark hadronisation produces a spectrum of dark mesons, including the dark pions $ \tilde{\pi}_{1} $, $ \tilde{\pi}_{2} $ and $ \tilde{\pi}_{3} $. The $ \tilde{\pi}_{3} $ then decays into SM fermions $ f\bar{f} $ through the dark photon $ \mathrm{A}' $. Green is used to indicate a long-lived particle. The $ \mathrm{A}' $ is a long-lived particle in Scenario A, while $ \tilde{\pi}_{3} $ is a long-lived particle in Scenario B1. |
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Figure 2-b:
Diagrams for the Scenario A model (left) and the Scenario B1 model (right). In these extended models the dark hadronisation produces a spectrum of dark mesons, including the dark pions $ \tilde{\pi}_{1} $, $ \tilde{\pi}_{2} $ and $ \tilde{\pi}_{3} $. The $ \tilde{\pi}_{3} $ then decays into SM fermions $ f\bar{f} $ through the dark photon $ \mathrm{A}' $. Green is used to indicate a long-lived particle. The $ \mathrm{A}' $ is a long-lived particle in Scenario A, while $ \tilde{\pi}_{3} $ is a long-lived particle in Scenario B1. |
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Figure 3:
Distributions of examples of variables that are used in the BDT training for the QCD background and benchmark signal models: muon multiplicity (upper) and muon transverse impact parameter (lower). |
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Figure 3-a:
Distributions of examples of variables that are used in the BDT training for the QCD background and benchmark signal models: muon multiplicity (upper) and muon transverse impact parameter (lower). |
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Figure 3-b:
Distributions of examples of variables that are used in the BDT training for the QCD background and benchmark signal models: muon multiplicity (upper) and muon transverse impact parameter (lower). |
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Figure 4:
Distributions of the multiplicity of dark vector mesons $ \tilde{\omega} $ for representative vector portal models (upper), and the multiplicity of dark mesons $ \tilde{\pi}_{3} $ for representative Scenario A and B1 models (lower). |
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Figure 4-a:
Distributions of the multiplicity of dark vector mesons $ \tilde{\omega} $ for representative vector portal models (upper), and the multiplicity of dark mesons $ \tilde{\pi}_{3} $ for representative Scenario A and B1 models (lower). |
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Figure 4-b:
Distributions of the multiplicity of dark vector mesons $ \tilde{\omega} $ for representative vector portal models (upper), and the multiplicity of dark mesons $ \tilde{\pi}_{3} $ for representative Scenario A and B1 models (lower). |
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Figure 5:
Dimuon invariant mass distributions for each single-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 5-a:
Dimuon invariant mass distributions for each single-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 5-b:
Dimuon invariant mass distributions for each single-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 5-c:
Dimuon invariant mass distributions for each single-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 5-d:
Dimuon invariant mass distributions for each single-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 5-e:
Dimuon invariant mass distributions for each single-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 5-f:
Dimuon invariant mass distributions for each single-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 6:
Dimuon invariant mass distributions for each multi-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 6-a:
Dimuon invariant mass distributions for each multi-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 6-b:
Dimuon invariant mass distributions for each multi-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 6-c:
Dimuon invariant mass distributions for each multi-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 6-d:
Dimuon invariant mass distributions for each multi-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 6-e:
Dimuon invariant mass distributions for each multi-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 6-f:
Dimuon invariant mass distributions for each multi-vertex category for data and two vector portal model signal benchmarks. The shaded regions indicate mass regions of known SM resonances, which are masked in the search. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. |
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Figure 7:
Dimuon invariant mass distributions in mass windows around 0.67 GeV (upper) and 1.33 GeV (lower), in the single-vertex category with 1 $ \text{cm} < l_{xy} < 10 $ cm and $ \text{pointing angle} < $ 0.2. The background fit is shown together with the signal expected for a representative Scenario A model (upper) and a representative Scenario B1 model (lower). A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. The lower panel in each plot shows the pull distribution, defined as the difference between the data and the background fit in each bin divided by the statistical uncertainty. |
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Figure 7-a:
Dimuon invariant mass distributions in mass windows around 0.67 GeV (upper) and 1.33 GeV (lower), in the single-vertex category with 1 $ \text{cm} < l_{xy} < 10 $ cm and $ \text{pointing angle} < $ 0.2. The background fit is shown together with the signal expected for a representative Scenario A model (upper) and a representative Scenario B1 model (lower). A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. The lower panel in each plot shows the pull distribution, defined as the difference between the data and the background fit in each bin divided by the statistical uncertainty. |
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Figure 7-b:
Dimuon invariant mass distributions in mass windows around 0.67 GeV (upper) and 1.33 GeV (lower), in the single-vertex category with 1 $ \text{cm} < l_{xy} < 10 $ cm and $ \text{pointing angle} < $ 0.2. The background fit is shown together with the signal expected for a representative Scenario A model (upper) and a representative Scenario B1 model (lower). A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. The lower panel in each plot shows the pull distribution, defined as the difference between the data and the background fit in each bin divided by the statistical uncertainty. |
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Figure 8:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\omega} $ meson $ c\tau $ for representative $ \tilde{\omega} $ mass hypotheses and branching fractions for decaying into a muon pair in the vector portal model. It is assumed that $ m_{\tilde{\omega}}=\tilde{\Lambda}=m_{\tilde{\eta}} $, where $ m_{\tilde{\omega}} $, $ \tilde{\Lambda} $, and $ m_{\tilde{\eta}} $ are parameters of the dark sector: the mass of the spin-one meson, confinement scale, and the mass of the spin-zero meson, respectively. |
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Figure 8-a:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\omega} $ meson $ c\tau $ for representative $ \tilde{\omega} $ mass hypotheses and branching fractions for decaying into a muon pair in the vector portal model. It is assumed that $ m_{\tilde{\omega}}=\tilde{\Lambda}=m_{\tilde{\eta}} $, where $ m_{\tilde{\omega}} $, $ \tilde{\Lambda} $, and $ m_{\tilde{\eta}} $ are parameters of the dark sector: the mass of the spin-one meson, confinement scale, and the mass of the spin-zero meson, respectively. |
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Figure 8-b:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\omega} $ meson $ c\tau $ for representative $ \tilde{\omega} $ mass hypotheses and branching fractions for decaying into a muon pair in the vector portal model. It is assumed that $ m_{\tilde{\omega}}=\tilde{\Lambda}=m_{\tilde{\eta}} $, where $ m_{\tilde{\omega}} $, $ \tilde{\Lambda} $, and $ m_{\tilde{\eta}} $ are parameters of the dark sector: the mass of the spin-one meson, confinement scale, and the mass of the spin-zero meson, respectively. |
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Figure 8-c:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\omega} $ meson $ c\tau $ for representative $ \tilde{\omega} $ mass hypotheses and branching fractions for decaying into a muon pair in the vector portal model. It is assumed that $ m_{\tilde{\omega}}=\tilde{\Lambda}=m_{\tilde{\eta}} $, where $ m_{\tilde{\omega}} $, $ \tilde{\Lambda} $, and $ m_{\tilde{\eta}} $ are parameters of the dark sector: the mass of the spin-one meson, confinement scale, and the mass of the spin-zero meson, respectively. |
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Figure 8-d:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\omega} $ meson $ c\tau $ for representative $ \tilde{\omega} $ mass hypotheses and branching fractions for decaying into a muon pair in the vector portal model. It is assumed that $ m_{\tilde{\omega}}=\tilde{\Lambda}=m_{\tilde{\eta}} $, where $ m_{\tilde{\omega}} $, $ \tilde{\Lambda} $, and $ m_{\tilde{\eta}} $ are parameters of the dark sector: the mass of the spin-one meson, confinement scale, and the mass of the spin-zero meson, respectively. |
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Figure 9:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' c\tau $ for representative $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ mass hypotheses, and branching fractions of the dark photon decaying into a muon pair in Scenario A. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. |
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Figure 9-a:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' c\tau $ for representative $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ mass hypotheses, and branching fractions of the dark photon decaying into a muon pair in Scenario A. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. |
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Figure 9-b:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' c\tau $ for representative $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ mass hypotheses, and branching fractions of the dark photon decaying into a muon pair in Scenario A. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. |
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Figure 9-c:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' c\tau $ for representative $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ mass hypotheses, and branching fractions of the dark photon decaying into a muon pair in Scenario A. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. |
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Figure 9-d:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' c\tau $ for representative $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ mass hypotheses, and branching fractions of the dark photon decaying into a muon pair in Scenario A. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. |
png pdf |
Figure 10:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\pi}_{3} $ meson $ c\tau $ for representative $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ mass hypotheses, and branching fractions of the dark photon decaying into a muon pair in Scenario B1. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. |
png pdf |
Figure 10-a:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\pi}_{3} $ meson $ c\tau $ for representative $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ mass hypotheses, and branching fractions of the dark photon decaying into a muon pair in Scenario B1. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. |
png pdf |
Figure 10-b:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\pi}_{3} $ meson $ c\tau $ for representative $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ mass hypotheses, and branching fractions of the dark photon decaying into a muon pair in Scenario B1. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. |
png pdf |
Figure 10-c:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\pi}_{3} $ meson $ c\tau $ for representative $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ mass hypotheses, and branching fractions of the dark photon decaying into a muon pair in Scenario B1. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. |
png pdf |
Figure 10-d:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\pi}_{3} $ meson $ c\tau $ for representative $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ mass hypotheses, and branching fractions of the dark photon decaying into a muon pair in Scenario B1. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. |
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Figure 11:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\omega} $ meson mass for representative $ c\tau $ hypotheses in the vector portal model. It is assumed that $ m_{\tilde{\omega}}=\tilde{\Lambda}=m_{\tilde{\eta}} $, where $ m_{\tilde{\omega}} $, $ \tilde{\Lambda} $, and $ m_{\tilde{\eta}} $ are parameters of the dark sector: the mass of the spin-one meson, confinement scale, and the mass of the spin-zero meson, respectively. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
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Figure 11-a:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\omega} $ meson mass for representative $ c\tau $ hypotheses in the vector portal model. It is assumed that $ m_{\tilde{\omega}}=\tilde{\Lambda}=m_{\tilde{\eta}} $, where $ m_{\tilde{\omega}} $, $ \tilde{\Lambda} $, and $ m_{\tilde{\eta}} $ are parameters of the dark sector: the mass of the spin-one meson, confinement scale, and the mass of the spin-zero meson, respectively. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
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Figure 11-b:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \tilde{\omega} $ meson mass for representative $ c\tau $ hypotheses in the vector portal model. It is assumed that $ m_{\tilde{\omega}}=\tilde{\Lambda}=m_{\tilde{\eta}} $, where $ m_{\tilde{\omega}} $, $ \tilde{\Lambda} $, and $ m_{\tilde{\eta}} $ are parameters of the dark sector: the mass of the spin-one meson, confinement scale, and the mass of the spin-zero meson, respectively. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
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Figure 12:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass in Scenario A, for representative $ \mathrm{A}' c\tau $ hypotheses, and different ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left column) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right column), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
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Figure 12-a:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass in Scenario A, for representative $ \mathrm{A}' c\tau $ hypotheses, and different ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left column) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right column), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 12-b:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass in Scenario A, for representative $ \mathrm{A}' c\tau $ hypotheses, and different ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left column) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right column), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 12-c:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass in Scenario A, for representative $ \mathrm{A}' c\tau $ hypotheses, and different ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left column) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right column), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 12-d:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass in Scenario A, for representative $ \mathrm{A}' c\tau $ hypotheses, and different ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left column) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right column), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
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Figure 13:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass in Scenario B1, for representative $ \tilde{\pi}_{3} c\tau $ hypotheses, and different ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left column) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right column), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 13-a:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass in Scenario B1, for representative $ \tilde{\pi}_{3} c\tau $ hypotheses, and different ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left column) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right column), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 13-b:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass in Scenario B1, for representative $ \tilde{\pi}_{3} c\tau $ hypotheses, and different ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left column) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right column), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 13-c:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass in Scenario B1, for representative $ \tilde{\pi}_{3} c\tau $ hypotheses, and different ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left column) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right column), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 13-d:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass in Scenario B1, for representative $ \tilde{\pi}_{3} c\tau $ hypotheses, and different ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left column) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right column), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 14:
Observed upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as a function of the $ \tilde{\omega} $ meson mass and $ c\tau $ in the vector portal model. The parameter space region that is omitted is kinematically forbidden in the model. It is assumed that $ m_{\tilde{\omega}}=\tilde{\Lambda}=m_{\tilde{\eta}} $, where $ m_{\tilde{\omega}} $, $ \tilde{\Lambda} $, and $ m_{\tilde{\eta}} $ are parameters of the dark sector: the mass of the spin-one meson, confinement scale, and the mass of the spin-zero meson, respectively. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 15:
Observed upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass and $ c\tau $ for representative ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses in Scenario A. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 15-a:
Observed upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass and $ c\tau $ for representative ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses in Scenario A. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 15-b:
Observed upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass and $ c\tau $ for representative ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses in Scenario A. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark-sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be 1. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 16:
Observed upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass and the $ \tilde{\pi}_{3} c\tau $ for representative ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses in Scenario B1. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be one. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 16-a:
Observed upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass and the $ \tilde{\pi}_{3} c\tau $ for representative ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses in Scenario B1. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be one. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
png pdf |
Figure 16-b:
Observed upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\psi\overline{\psi}) $ as functions of the $ \mathrm{A}' $ mass and the $ \tilde{\pi}_{3} c\tau $ for representative ratios of the $ \tilde{\pi}_{3} $ and $ \mathrm{A}' $ masses in Scenario B1. The limits are shown for the cases where $ m_{\tilde{\pi}_{3}}=10m_{\mathrm{A}'} $ (left) and $ m_{\tilde{\pi}_{3}}=3m_{\mathrm{A}'} $ (right), respectively. It is assumed that $ m_{\tilde{\eta}}=\tilde{\Lambda}=4m_{\tilde{\pi}_{2}} $ and $ {\sin\theta=0.1} $, where $ m_{\tilde{\eta}} $ is the mass of the dark sector pseudoscalar meson and $ \theta $ is the mixing angle parametrising the isospin violation. The branching fraction $ \mathcal{B}(\tilde{\pi}_{3}\to \mathrm{A}'\mathrm{A}') $ is assumed to be one. The grey bands correspond to mass regions of known SM resonances, which are masked in the search. |
| Tables | |
png pdf |
Table 1:
Model parameters of the different classes of signal models interpreted by the analysis. |
png pdf |
Table 2:
The SM resonances and the corresponding mass windows that are masked in the analysis. |
png pdf |
Table 3:
Summary of the systematic uncertainties in the signal yield expectation. |
| Summary |
| A search for dark showers has been performed with non-prompt muon pairs, using proton-proton collisions at the CERN LHC at a centre-of-mass energy of 13 TeV, collected by the CMS experiment in 2018, corresponding to an integrated luminosity of 41.6 fb$ ^{-1} $. The data set is recorded using the data parking strategy, resulting in a sample of about $ 10^{10} $ recorded events, giving access to masses down to the sub-GeV scale. No significant excess beyond the standard model expectation is observed. Upper limits on the branching fraction of the Higgs boson decaying into dark partons are set as low as $ 10^{-4} $ at 95% confidence level, providing the most stringent limits to date on the vector portal model with dark $ \tilde{\omega} $ mesons of mean proper decay length below 500 mm and masses between 0.3 and 20 GeV. For the first time, limits have been set for extended dark-shower models with two dark flavours (Scenario A and Scenario B1) that contain dark photons, probing their masses down to 0.33 GeV. |
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