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| CMS-PAS-EXO-21-008 | ||
| Search for long-lived particles decaying in the CMS muon detectors in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 12 July 2023 | ||
| Abstract: A search for long-lived particles (LLPs) decaying in the CMS muon detectors is presented. The data sample consists of 138 fb$ ^{-1} $ of proton-proton collisions at $ \sqrt{s}= $ 13 TeV, recorded at the LHC in 2016-2018. A unique technique is employed to reconstruct decays of LLPs in the muon detectors. The search is sensitive to LLP masses from 0.4 to 55 GeV and a broad range of LLP decay modes, including decays to a pair of quarks, kaons, pions, electrons, photons, or $ \tau $ leptons. No excess of events above the standard model background is observed. The most stringent LHC limits to date on the branching fraction of the Higgs boson to a pair of LLPs with masses below 10 GeV are set. This search also provides the most stringent limit for proper decay lengths in the range 0.04-0.4 m and above 4 m for an LLP mass of 15 GeV, in the range 0.3-0.9 m and above 3 m for an LLP mass of 40 GeV, and above 0.8 m for an LLP mass of 55 GeV. Finally, this search sets the first LHC limits on a dark quantum chromodynamic sector that couples to the Higgs boson through gluon, Higgs, photon, vector, and dark photon portals, and is sensitive to branching fractions of the Higgs boson to dark quarks as low as 10$^{-3} $. | ||
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Links:
CDS record (PDF) ;
Physics Briefing ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to PRD. The superseded preliminary plots can be found here. |
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| Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1:
Diagram of twin Higgs model and dark shower model. The SM Higgs boson decays to a pair of neutral long-lived scalars (S) in the twin Higgs model or to a pair of dark sector quarks ($ \Psi $) in the dark shower model. |
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Figure 2:
The cluster reconstruction efficiencies, including both DT and CSC clusters, as a function of the simulated $ r $ and $ |z| $ decay positions of the particle S decaying to $ \mathrm{d}\overline{\mathrm{d}} $, for a mass of 40 GeV and a range of $ c\tau $ values between 1 and 10 m. The barrel and endcap muon stations are drawn as black boxes and labeled by their station names. Regions occupied by steel shielding are shaded in gray. |
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Figure 3:
The DT (left) and CSC (right) cluster reconstruction efficiency as a function of the simulated $ r $ or $ |z| $ decay positions of S decaying to $ \mathrm{d}\overline{\mathrm{d}} $, for a mass of 40 GeV and a range of $ c\tau $ values between 1 and 10 m. Regions occupied by steel shielding are shaded in gray. |
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Figure 3-a:
The DT (left) and CSC (right) cluster reconstruction efficiency as a function of the simulated $ r $ or $ |z| $ decay positions of S decaying to $ \mathrm{d}\overline{\mathrm{d}} $, for a mass of 40 GeV and a range of $ c\tau $ values between 1 and 10 m. Regions occupied by steel shielding are shaded in gray. |
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Figure 3-b:
The DT (left) and CSC (right) cluster reconstruction efficiency as a function of the simulated $ r $ or $ |z| $ decay positions of S decaying to $ \mathrm{d}\overline{\mathrm{d}} $, for a mass of 40 GeV and a range of $ c\tau $ values between 1 and 10 m. Regions occupied by steel shielding are shaded in gray. |
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Figure 4:
The geometric acceptance and the efficiency of the $ p_{\mathrm{T}}^\text{miss} \geq $ 200 GeV selection as a function of S proper decay length for a mass of 40 GeV. |
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Figure 5:
Distributions of cluster time are shown for S decaying to $ \mathrm{d}\overline{\mathrm{d}} $ for a proper decay length of 1 m and mass of 40 GeV, and for a background-enriched sample in data selected by inverting the $ N_\text{hits} $ requirement. The distributions are normalized to unit area. |
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Figure 6:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) are shown for S decaying to $ \mathrm{d}\overline{\mathrm{d}} $ for a proper decay length of 1 m and various masses compared to the OOT background ($ t_\text{cluster} < - $ 12.5 ns). The distributions are normalized to unit area. The OOT background is representative of the overall background shape, because the background passing all the selections described above is dominated by pileup and underlying events. |
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Figure 6-a:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) are shown for S decaying to $ \mathrm{d}\overline{\mathrm{d}} $ for a proper decay length of 1 m and various masses compared to the OOT background ($ t_\text{cluster} < - $ 12.5 ns). The distributions are normalized to unit area. The OOT background is representative of the overall background shape, because the background passing all the selections described above is dominated by pileup and underlying events. |
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Figure 6-b:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) are shown for S decaying to $ \mathrm{d}\overline{\mathrm{d}} $ for a proper decay length of 1 m and various masses compared to the OOT background ($ t_\text{cluster} < - $ 12.5 ns). The distributions are normalized to unit area. The OOT background is representative of the overall background shape, because the background passing all the selections described above is dominated by pileup and underlying events. |
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Figure 7:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) for DT clusters are shown for S decaying to $ \mathrm{d}\overline{\mathrm{d}} $ for a proper decay length of 1 m and various masses compared to the shape of background in a selection where the cluster is not matched to any RPC hit. The distributions are normalized to unit area. |
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Figure 7-a:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) for DT clusters are shown for S decaying to $ \mathrm{d}\overline{\mathrm{d}} $ for a proper decay length of 1 m and various masses compared to the shape of background in a selection where the cluster is not matched to any RPC hit. The distributions are normalized to unit area. |
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Figure 7-b:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) for DT clusters are shown for S decaying to $ \mathrm{d}\overline{\mathrm{d}} $ for a proper decay length of 1 m and various masses compared to the shape of background in a selection where the cluster is not matched to any RPC hit. The distributions are normalized to unit area. |
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Figure 8:
Diagrams illustrating the ABCD plane for the DT-CSC category (left) and for the DT-DT and CSC-CSC categories (right). The variable $ c_1 $ is the pass-fail ratio of the $ N_\text{hits} $ selection for the background cluster. Bin A is the signal region for all categories. |
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Figure 9:
Diagram illustrating the ABCD plane for the single CSC cluster category. Bin A is the signal region. |
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Figure 10:
Distributions of $ N_\text{clusters} $ passing the $ N_\text{hits} $ selection in the search region for CSC-CSC (left), DT-DT (center), and DT-CSC (right) categories. The background predicted by the fit is shown in blue with the shaded region showing the fitted uncertainty. The expected signal with $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%, $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $, and $ c\tau= $ 1 m is shown for $ m_\mathrm{S} $ of 3, 7, 15, 40, and 55 GeV in various colors and dotted lines. |
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Figure 10-a:
Distributions of $ N_\text{clusters} $ passing the $ N_\text{hits} $ selection in the search region for CSC-CSC (left), DT-DT (center), and DT-CSC (right) categories. The background predicted by the fit is shown in blue with the shaded region showing the fitted uncertainty. The expected signal with $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%, $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $, and $ c\tau= $ 1 m is shown for $ m_\mathrm{S} $ of 3, 7, 15, 40, and 55 GeV in various colors and dotted lines. |
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Figure 10-b:
Distributions of $ N_\text{clusters} $ passing the $ N_\text{hits} $ selection in the search region for CSC-CSC (left), DT-DT (center), and DT-CSC (right) categories. The background predicted by the fit is shown in blue with the shaded region showing the fitted uncertainty. The expected signal with $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%, $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $, and $ c\tau= $ 1 m is shown for $ m_\mathrm{S} $ of 3, 7, 15, 40, and 55 GeV in various colors and dotted lines. |
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Figure 10-c:
Distributions of $ N_\text{clusters} $ passing the $ N_\text{hits} $ selection in the search region for CSC-CSC (left), DT-DT (center), and DT-CSC (right) categories. The background predicted by the fit is shown in blue with the shaded region showing the fitted uncertainty. The expected signal with $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%, $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $, and $ c\tau= $ 1 m is shown for $ m_\mathrm{S} $ of 3, 7, 15, 40, and 55 GeV in various colors and dotted lines. |
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Figure 11:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) in the search region of the single CSC cluster category. The background predicted by the fit is shown in blue with the shaded region showing the fitted uncertainty. The expected signal with $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%, $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $, and $ c\tau= $ 1 m is shown for $ m_\mathrm{S} $ of 3, 7, 15, 40, and 55 GeV in various colors and dotted lines. The $ N_\text{hits} $ distribution includes only events in bins A and D, while the $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ one includes only events in bins A and B. The last bin in the $ N_\text{hits} $ distribution includes overflow events. |
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Figure 11-a:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) in the search region of the single CSC cluster category. The background predicted by the fit is shown in blue with the shaded region showing the fitted uncertainty. The expected signal with $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%, $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $, and $ c\tau= $ 1 m is shown for $ m_\mathrm{S} $ of 3, 7, 15, 40, and 55 GeV in various colors and dotted lines. The $ N_\text{hits} $ distribution includes only events in bins A and D, while the $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ one includes only events in bins A and B. The last bin in the $ N_\text{hits} $ distribution includes overflow events. |
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Figure 11-b:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) in the search region of the single CSC cluster category. The background predicted by the fit is shown in blue with the shaded region showing the fitted uncertainty. The expected signal with $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%, $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $, and $ c\tau= $ 1 m is shown for $ m_\mathrm{S} $ of 3, 7, 15, 40, and 55 GeV in various colors and dotted lines. The $ N_\text{hits} $ distribution includes only events in bins A and D, while the $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ one includes only events in bins A and B. The last bin in the $ N_\text{hits} $ distribution includes overflow events. |
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Figure 12:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) in the search region of the single DT cluster category. The background predicted by the fit is shown in blue with the shaded region showing the fitted uncertainty. The expected signal with $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%, $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $, and $ c\tau= $ 1 m is shown for $ m_\mathrm{S} $ of 3, 7, 15, 40, and 55 GeV in various colors and dotted lines. The $ N_\text{hits} $ distribution includes only events in bins A and D, while the $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ one includes only events in bins A and B. The last bin in the $ N_\text{hits} $ distribution includes overflow events. |
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Figure 12-a:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) in the search region of the single DT cluster category. The background predicted by the fit is shown in blue with the shaded region showing the fitted uncertainty. The expected signal with $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%, $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $, and $ c\tau= $ 1 m is shown for $ m_\mathrm{S} $ of 3, 7, 15, 40, and 55 GeV in various colors and dotted lines. The $ N_\text{hits} $ distribution includes only events in bins A and D, while the $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ one includes only events in bins A and B. The last bin in the $ N_\text{hits} $ distribution includes overflow events. |
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Figure 12-b:
Distributions of $ N_\text{hits} $ (left) and $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ (right) in the search region of the single DT cluster category. The background predicted by the fit is shown in blue with the shaded region showing the fitted uncertainty. The expected signal with $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%, $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $, and $ c\tau= $ 1 m is shown for $ m_\mathrm{S} $ of 3, 7, 15, 40, and 55 GeV in various colors and dotted lines. The $ N_\text{hits} $ distribution includes only events in bins A and D, while the $ \Delta\phi{\mathrm{(}{\vec p}_{\mathrm{T}}^{\ \text{miss}}\mathrm{, cluster)}} $ one includes only events in bins A and B. The last bin in the $ N_\text{hits} $ distribution includes overflow events. |
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Figure 13:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of $ c\tau $ for the $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $ (top left), $ \mathrm{S}\to\pi^{0}\pi^{0} $ (top right), and $ \mathrm{S}\to\tau^{+}\tau^{-} $ (bottom) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 3, 7, 15, 40, and 55 GeV. |
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Figure 13-a:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of $ c\tau $ for the $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $ (top left), $ \mathrm{S}\to\pi^{0}\pi^{0} $ (top right), and $ \mathrm{S}\to\tau^{+}\tau^{-} $ (bottom) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 3, 7, 15, 40, and 55 GeV. |
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Figure 13-b:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of $ c\tau $ for the $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $ (top left), $ \mathrm{S}\to\pi^{0}\pi^{0} $ (top right), and $ \mathrm{S}\to\tau^{+}\tau^{-} $ (bottom) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 3, 7, 15, 40, and 55 GeV. |
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Figure 13-c:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of $ c\tau $ for the $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $ (top left), $ \mathrm{S}\to\pi^{0}\pi^{0} $ (top right), and $ \mathrm{S}\to\tau^{+}\tau^{-} $ (bottom) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 3, 7, 15, 40, and 55 GeV. |
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Figure 14:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $ (top left), $ \mathrm{S}\to\pi^{0}\pi^{0} $ (top right), and $ \mathrm{S}\to\tau^{+}\tau^{-} $ (bottom) decay modes. |
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Figure 14-a:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $ (top left), $ \mathrm{S}\to\pi^{0}\pi^{0} $ (top right), and $ \mathrm{S}\to\tau^{+}\tau^{-} $ (bottom) decay modes. |
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Figure 14-b:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $ (top left), $ \mathrm{S}\to\pi^{0}\pi^{0} $ (top right), and $ \mathrm{S}\to\tau^{+}\tau^{-} $ (bottom) decay modes. |
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Figure 14-c:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{d}\overline{\mathrm{d}} $ (top left), $ \mathrm{S}\to\pi^{0}\pi^{0} $ (top right), and $ \mathrm{S}\to\tau^{+}\tau^{-} $ (bottom) decay modes. |
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Figure 15:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $, assuming the branching fractions for S calculated in Ref. [67]. |
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Figure 16:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the gluon portal (top left) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (2.5, 1), photon portal (top right) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (2.5, 1), and vector portal (bottom) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (1, 1). The exclusion limits are shown for different LLP mass hypotheses: 2, 5, 10, 15, and 20 GeV. |
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Figure 16-a:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the gluon portal (top left) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (2.5, 1), photon portal (top right) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (2.5, 1), and vector portal (bottom) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (1, 1). The exclusion limits are shown for different LLP mass hypotheses: 2, 5, 10, 15, and 20 GeV. |
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Figure 16-b:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the gluon portal (top left) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (2.5, 1), photon portal (top right) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (2.5, 1), and vector portal (bottom) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (1, 1). The exclusion limits are shown for different LLP mass hypotheses: 2, 5, 10, 15, and 20 GeV. |
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Figure 16-c:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the gluon portal (top left) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (2.5, 1), photon portal (top right) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (2.5, 1), and vector portal (bottom) assuming $ (x_{i\omega} $, $ x_{i\Lambda}) = $ (1, 1). The exclusion limits are shown for different LLP mass hypotheses: 2, 5, 10, 15, and 20 GeV. |
| Tables | |
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Table 1:
Comparison between the ABCD predicted and observed yields in both validation regions for the double cluster category. The uncertainty of the prediction is the statistical uncertainty propagated from bins B, C, and D or bins BD and C. The symbol $ \lambda_\mathrm{X} $ is the expected background event rate in bin X, while $ N_\mathrm{X} $ is the observed number of events in bin X. |
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Table 2:
Comparison between the ABCD predicted and observed yields in the validation regions for the single CSC cluster category. The uncertainty of the prediction is the statistical uncertainty propagated from bins B, C, and D. The symbol $ \lambda_\mathrm{X} $ is the expected background event rate in bin X, while $ N_\mathrm{X} $ is the observed number of events in bin X. |
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Table 3:
Comparison between the ABCD predicted and observed yields in a pileup-enriched region for the single DT cluster category. The uncertainty of the prediction is the statistical uncertainty propagated from bins B, C, and D. Bins C and D for MB3 and MB4 categories are combined to reduce statistical uncertainty in the two regions. The final ABCD fit in the signal region will also be performed with those bins combined. |
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Table 4:
Validation of the punch-through jet background prediction method for the single DT cluster category. The uncertainty of the prediction is the statistical uncertainty propagated from the extrapolated MB1/MB2 hit veto efficiency. |
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Table 5:
Number of predicted background and observed events in the double cluster category. |
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Table 6:
Number of predicted background and observed events in the single CSC cluster category. |
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Table 7:
Number of predicted background and observed events in the single DT cluster category. |
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Table 8:
Number of signal events in bin A for each category for a few benchmark signal models assuming $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) = $ 1%. |
| Summary |
| In summary, proton-proton collision data at $ \sqrt{s} = $ 13 TeV recorded by the CMS experiment in 2016--2018, corresponding to an integrated luminosity of 138 fb$ ^{-1} $, have been used to conduct the first search that uses both the barrel and endcap CMS muon detectors to detect hadronic and electromagnetic showers from long-lived particle (LLP) decays. Based on the unique detector signature, the search is largely model-independent, with sensitivity to a broad range of LLP decay modes and masses below the GeV scale. With the excellent shielding provided by the inner CMS detector, the CMS magnet, and the steel return yoke, the background is suppressed to a low level and a search for both single and double LLP decays is possible. No significant deviation from the standard model background is observed. The most stringent LHC constraints to date are set on the branching fraction of the Higgs boson to LLPs with masses below 10 GeV and decaying to particles other than muons. The search provides the most stringent branching fraction limit for proper decay lengths in the range 0.04-0.4 m and above 4 m for an LLP mass of 15 GeV, in the range 0.3-0.9 m and above 3 m for an LLP mass of 40 GeV, and above 0.8 m for an LLP mass of 55 GeV. Finally, the first LHC limits on models of dark showers produced via Higgs boson decay are set, and constrain branching fractions of the Higgs boson decay to dark quarks as low as 10$^{-3} $. |
| Additional Figures | |
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Additional Figure 1:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as functions of $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to \gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 1.5, 3, 15, 40, and 55 GeV. |
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Additional Figure 1-a:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as functions of $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to \gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 1.5, 3, 15, 40, and 55 GeV. |
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Additional Figure 1-b:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as functions of $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to \gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 1.5, 3, 15, 40, and 55 GeV. |
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Additional Figure 1-c:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as functions of $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to \gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 1.5, 3, 15, 40, and 55 GeV. |
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Additional Figure 1-d:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as functions of $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to \gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 1.5, 3, 15, 40, and 55 GeV. |
png pdf |
Additional Figure 1-e:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as functions of $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to \gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 1.5, 3, 15, 40, and 55 GeV. |
png pdf |
Additional Figure 1-f:
The 95% CL expected (dotted curves) and observed (solid curves) upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as functions of $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to \gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. The exclusion limits are shown for different mass hypotheses: 0.4, 1, 1.5, 3, 15, 40, and 55 GeV. |
png pdf |
Additional Figure 2:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to\gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. |
png pdf |
Additional Figure 2-a:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to\gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. |
png pdf |
Additional Figure 2-b:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to\gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. |
png pdf |
Additional Figure 2-c:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to\gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. |
png pdf |
Additional Figure 2-d:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to\gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. |
png pdf |
Additional Figure 2-e:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to\gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. |
png pdf |
Additional Figure 2-f:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{S}\mathrm{S}) $ as a function of mass and $ c\tau $ for the $ \mathrm{S}\to\mathrm{b}\overline{\mathrm{b}} $ (top left), $ \mathrm{S}\to\pi^{+}\pi^{-} $ (top center), and $ \mathrm{S}\to \mathrm{K^+}\mathrm{K^-} $ (top right), $ \mathrm{S}\to \mathrm{K^0}\mathrm{K^0} $ (bottom left), $ \mathrm{S}\to\gamma\gamma $ (bottom center), $ \mathrm{S}\to \mathrm{e}^+\mathrm{e}^- $ (bottom right) decay modes. |
png pdf |
Additional Figure 3:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the gluon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 5, 10, 15, and 20 GeV. The center panel is shown again in the appendix, for completeness. |
png pdf |
Additional Figure 3-a:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the gluon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 5, 10, 15, and 20 GeV. The center panel is shown again in the appendix, for completeness. |
png pdf |
Additional Figure 3-b:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the gluon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 5, 10, 15, and 20 GeV. The center panel is shown again in the appendix, for completeness. |
png pdf |
Additional Figure 3-c:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the gluon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 5, 10, 15, and 20 GeV. The center panel is shown again in the appendix, for completeness. |
png pdf |
Additional Figure 4:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the photon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 2, 5, 10, 15, and 20 GeV. The center limit plot is shown again in the appendix, for completeness. |
png pdf |
Additional Figure 4-a:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the photon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 2, 5, 10, 15, and 20 GeV. The center limit plot is shown again in the appendix, for completeness. |
png pdf |
Additional Figure 4-b:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the photon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 2, 5, 10, 15, and 20 GeV. The center limit plot is shown again in the appendix, for completeness. |
png pdf |
Additional Figure 4-c:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the photon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 2, 5, 10, 15, and 20 GeV. The center limit plot is shown again in the appendix, for completeness. |
png pdf |
Additional Figure 5:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the Higgs portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 4, 5, 10, 15, and 20 GeV. |
png pdf |
Additional Figure 5-a:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the Higgs portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 4, 5, 10, 15, and 20 GeV. |
png pdf |
Additional Figure 5-b:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the Higgs portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 4, 5, 10, 15, and 20 GeV. |
png pdf |
Additional Figure 5-c:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the Higgs portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 4, 5, 10, 15, and 20 GeV. |
png pdf |
Additional Figure 6:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the dark photon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 5, 10, 15, and 20 GeV. |
png pdf |
Additional Figure 6-a:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the dark photon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 5, 10, 15, and 20 GeV. |
png pdf |
Additional Figure 6-b:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the dark photon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 5, 10, 15, and 20 GeV. |
png pdf |
Additional Figure 6-c:
The 95% CL observed upper limits on the branching fraction $ \mathcal{B}(\mathrm{h}^0\to\Psi\Psi) $ as functions of $ c\tau $ for the dark photon portal, assuming $ x_{i\omega} = x_{i\Lambda} = $ 1.0 (left), $ x_{i\omega} = 2.5, x_{i\Lambda} = $ 1.0 (center), and $ x_{i\omega} = x_{i\Lambda} = $ 2.5 (right). The exclusion limits are shown for different mass hypotheses: 5, 10, 15, and 20 GeV. |
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