Compact Muon Solenoid
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| CMS-EXO-24-016 ; CERN-EP-2026-132 | ||
| Search for long-lived particles decaying into muons in proton-proton collisions at $ \sqrt{s} = $ 13.6 TeV using data scouting | ||
| CMS Collaboration | ||
| 24 June 2026 | ||
| Submitted to the Journal of High Energy Physics | ||
| Abstract: A search for long-lived particles decaying into muons is performed using proton-proton collisions at $ \sqrt{s}= $ 13.6 TeV, collected by the CMS experiment at the LHC in 2022 and 2023, corresponding to an integrated luminosity of 62.4 fb$ ^{-1} $. The data were collected using dedicated dimuon triggers with low transverse momentum thresholds, recorded with a high-rate data scouting trigger stream. This data stream retains a reduced amount of information at the high-level trigger, to explore otherwise inaccessible phase space at low multimuon invariant mass and nonzero displacement from the primary interaction vertex. No significant excess of events above the standard model prediction is found. Upper limits on branching fractions at 95% confidence level are set for a wide range of mass and lifetime hypotheses in several beyond the standard model frameworks, where the Higgs boson decays into long-lived dark photons or into dark partons that produce showers containing long-lived particles, or where a long-lived scalar resonance is produced from the decay of a b hadron. The resulting constraints improve and extend existing ones in large regions of the parameter space. | ||
| Links: e-print arXiv:2606.25840 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Diagrams illustrating an SM-like Higgs boson (H) decay to four fermions ($ f $) via two intermediate dark photons, $ \mathrm{Z}_{\mathrm{D}} $ [6]: through the hypercharge portal (left) and the Higgs portal (right) via a dark Higgs boson ($ \mathrm{H}_{\mathrm{D}} $). The long-lived particles are highlighted in green. |
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Figure 1-a:
Diagrams illustrating an SM-like Higgs boson (H) decay to four fermions ($ f $) via two intermediate dark photons, $ \mathrm{Z}_{\mathrm{D}} $ [6]: through the hypercharge portal (left) and the Higgs portal (right) via a dark Higgs boson ($ \mathrm{H}_{\mathrm{D}} $). The long-lived particles are highlighted in green. |
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Figure 1-b:
Diagrams illustrating an SM-like Higgs boson (H) decay to four fermions ($ f $) via two intermediate dark photons, $ \mathrm{Z}_{\mathrm{D}} $ [6]: through the hypercharge portal (left) and the Higgs portal (right) via a dark Higgs boson ($ \mathrm{H}_{\mathrm{D}} $). The long-lived particles are highlighted in green. |
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Figure 2:
Diagrams illustrating two dark-shower scenarios [8], where a dark meson $ \tilde{\eta} $ is allowed to decay into dark pions ($ \tilde{\pi} _3 $), which in turn decay into pairs of dark photons ($ A^{\prime} $). Scenario A (left) assumes prompt $ \tilde{\pi} _3 $ decays into a pair of long-lived dark photons, $ A^{\prime} $, each decaying into fermions. Scenario B1 (right) assumes long-lived $ \tilde{\pi} _3 $ decays into a pair of promptly decaying dark photons ($ A^{\prime} $). The long-lived particles are highlighted in green. |
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Figure 2-a:
Diagrams illustrating two dark-shower scenarios [8], where a dark meson $ \tilde{\eta} $ is allowed to decay into dark pions ($ \tilde{\pi} _3 $), which in turn decay into pairs of dark photons ($ A^{\prime} $). Scenario A (left) assumes prompt $ \tilde{\pi} _3 $ decays into a pair of long-lived dark photons, $ A^{\prime} $, each decaying into fermions. Scenario B1 (right) assumes long-lived $ \tilde{\pi} _3 $ decays into a pair of promptly decaying dark photons ($ A^{\prime} $). The long-lived particles are highlighted in green. |
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Figure 2-b:
Diagrams illustrating two dark-shower scenarios [8], where a dark meson $ \tilde{\eta} $ is allowed to decay into dark pions ($ \tilde{\pi} _3 $), which in turn decay into pairs of dark photons ($ A^{\prime} $). Scenario A (left) assumes prompt $ \tilde{\pi} _3 $ decays into a pair of long-lived dark photons, $ A^{\prime} $, each decaying into fermions. Scenario B1 (right) assumes long-lived $ \tilde{\pi} _3 $ decays into a pair of promptly decaying dark photons ($ A^{\prime} $). The long-lived particles are highlighted in green. |
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Figure 3:
Diagram illustrating the production of a scalar resonance $ \phi $ in a b hadron decay, through the mixing with an SM-like Higgs boson (H). The long-lived particle $ \phi $ is highlighted in green. |
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Figure 4:
Overall signal efficiency as measured for the HAHM signal model with $ m_{\mathrm{Z}_{\mathrm{D}}} = 2, 5, $ 12, and 20 GeV, as a function of the mean proper decay length of the dark photon, $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}} $. The efficiency is defined as the fraction of events with at least one dark photon decaying into a muon pair, reconstructed as a dimuon candidate within the $ l_\mathrm{xy} $ bins of $ [0, 0.2, 1, 2.4, 3.1, 7, 11, 16, 70] \text{cm} $. The average efficiency over the 2022 and 2023 data-taking periods is shown. |
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Figure 4-a:
Overall signal efficiency as measured for the HAHM signal model with $ m_{\mathrm{Z}_{\mathrm{D}}} = 2, 5, $ 12, and 20 GeV, as a function of the mean proper decay length of the dark photon, $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}} $. The efficiency is defined as the fraction of events with at least one dark photon decaying into a muon pair, reconstructed as a dimuon candidate within the $ l_\mathrm{xy} $ bins of $ [0, 0.2, 1, 2.4, 3.1, 7, 11, 16, 70] \text{cm} $. The average efficiency over the 2022 and 2023 data-taking periods is shown. |
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Figure 4-b:
Overall signal efficiency as measured for the HAHM signal model with $ m_{\mathrm{Z}_{\mathrm{D}}} = 2, 5, $ 12, and 20 GeV, as a function of the mean proper decay length of the dark photon, $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}} $. The efficiency is defined as the fraction of events with at least one dark photon decaying into a muon pair, reconstructed as a dimuon candidate within the $ l_\mathrm{xy} $ bins of $ [0, 0.2, 1, 2.4, 3.1, 7, 11, 16, 70] \text{cm} $. The average efficiency over the 2022 and 2023 data-taking periods is shown. |
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Figure 4-c:
Overall signal efficiency as measured for the HAHM signal model with $ m_{\mathrm{Z}_{\mathrm{D}}} = 2, 5, $ 12, and 20 GeV, as a function of the mean proper decay length of the dark photon, $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}} $. The efficiency is defined as the fraction of events with at least one dark photon decaying into a muon pair, reconstructed as a dimuon candidate within the $ l_\mathrm{xy} $ bins of $ [0, 0.2, 1, 2.4, 3.1, 7, 11, 16, 70] \text{cm} $. The average efficiency over the 2022 and 2023 data-taking periods is shown. |
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Figure 4-d:
Overall signal efficiency as measured for the HAHM signal model with $ m_{\mathrm{Z}_{\mathrm{D}}} = 2, 5, $ 12, and 20 GeV, as a function of the mean proper decay length of the dark photon, $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}} $. The efficiency is defined as the fraction of events with at least one dark photon decaying into a muon pair, reconstructed as a dimuon candidate within the $ l_\mathrm{xy} $ bins of $ [0, 0.2, 1, 2.4, 3.1, 7, 11, 16, 70] \text{cm} $. The average efficiency over the 2022 and 2023 data-taking periods is shown. |
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Figure 5:
Four-muon invariant mass distributions of selected events in the multivertex (left) and overlapping vertex (right) categories, for data (black points with uncertainties) and representative signal models (colored histograms). |
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Figure 5-a:
Four-muon invariant mass distributions of selected events in the multivertex (left) and overlapping vertex (right) categories, for data (black points with uncertainties) and representative signal models (colored histograms). |
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Figure 5-b:
Four-muon invariant mass distributions of selected events in the multivertex (left) and overlapping vertex (right) categories, for data (black points with uncertainties) and representative signal models (colored histograms). |
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Figure 6:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 6-a:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 6-b:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 6-c:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 6-d:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 6-e:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 6-f:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 7:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV. Distributions are shown separately for each of the two $ l_\mathrm{xy} > 11 \text{cm} $ bins (i.e.,, for the displacement range inaccessible to the previous results presented in Ref. [18]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 7-a:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV. Distributions are shown separately for each of the two $ l_\mathrm{xy} > 11 \text{cm} $ bins (i.e.,, for the displacement range inaccessible to the previous results presented in Ref. [18]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 7-b:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV. Distributions are shown separately for each of the two $ l_\mathrm{xy} > 11 \text{cm} $ bins (i.e.,, for the displacement range inaccessible to the previous results presented in Ref. [18]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 8:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} < $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 8-a:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} < $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 8-b:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} < $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 8-c:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} < $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 8-d:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} < $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 8-e:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} < $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 8-f:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} < $ 25 GeV. Distributions are shown separately for each of the six $ l_\mathrm{xy} < 11 \text{cm} $ bins. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 9:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} < $ 25 GeV. Distributions are shown separately for each of the two $ l_\mathrm{xy} > 11 \text{cm} $ bins (i.e.,, for the displacement range inaccessible to the previous results presented in Ref. [18]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
png pdf |
Figure 9-a:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} < $ 25 GeV. Distributions are shown separately for each of the two $ l_\mathrm{xy} > 11 \text{cm} $ bins (i.e.,, for the displacement range inaccessible to the previous results presented in Ref. [18]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
png pdf |
Figure 9-b:
Dimuon invariant mass distributions of selected events with a single, isolated muon pair with $ p_{\mathrm{T}}^{\mu\mu} < $ 25 GeV. Distributions are shown separately for each of the two $ l_\mathrm{xy} > 11 \text{cm} $ bins (i.e.,, for the displacement range inaccessible to the previous results presented in Ref. [18]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. Distributions are shown as obtained in data (black points with uncertainties) and for representative signal models (colored histograms). |
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Figure 10:
The dimuon invariant mass distribution (left) is shown for data collected in 2022 (black markers) in a mass window centered around 5 GeV, in one of the dimuon search bins (0.2 $ < l_\mathrm{xy} < 1 \text{cm} $, $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV, with two isolated muons). The results of background+signal fits to the data of three selected functional forms are also shown (different colors, partially overlapping lines), highlighting the Bernstein polynomial as the best fit (solid, purple line) for this mass window. The corresponding pre-fit function (solid blue line) for a representative $ \mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}} $ signal, assuming a cross section of $ \sigma(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) = $ 100 fb, is shown for visualization purposes. The fit (solid blue line for the total fit function, and dashed red and orange lines for its individual components) to the dimuon invariant mass distribution (right) expected in the same dimuon search bin is shown for a representative $ \mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}} $ signal (black markers) with $ m_{\mathrm{Z}_{\mathrm{D}}}= $ 5 GeV and $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}}=1 \text{cm} $. |
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Figure 10-a:
The dimuon invariant mass distribution (left) is shown for data collected in 2022 (black markers) in a mass window centered around 5 GeV, in one of the dimuon search bins (0.2 $ < l_\mathrm{xy} < 1 \text{cm} $, $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV, with two isolated muons). The results of background+signal fits to the data of three selected functional forms are also shown (different colors, partially overlapping lines), highlighting the Bernstein polynomial as the best fit (solid, purple line) for this mass window. The corresponding pre-fit function (solid blue line) for a representative $ \mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}} $ signal, assuming a cross section of $ \sigma(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) = $ 100 fb, is shown for visualization purposes. The fit (solid blue line for the total fit function, and dashed red and orange lines for its individual components) to the dimuon invariant mass distribution (right) expected in the same dimuon search bin is shown for a representative $ \mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}} $ signal (black markers) with $ m_{\mathrm{Z}_{\mathrm{D}}}= $ 5 GeV and $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}}=1 \text{cm} $. |
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Figure 10-b:
The dimuon invariant mass distribution (left) is shown for data collected in 2022 (black markers) in a mass window centered around 5 GeV, in one of the dimuon search bins (0.2 $ < l_\mathrm{xy} < 1 \text{cm} $, $ p_{\mathrm{T}}^{\mu\mu} > $ 25 GeV, with two isolated muons). The results of background+signal fits to the data of three selected functional forms are also shown (different colors, partially overlapping lines), highlighting the Bernstein polynomial as the best fit (solid, purple line) for this mass window. The corresponding pre-fit function (solid blue line) for a representative $ \mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}} $ signal, assuming a cross section of $ \sigma(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) = $ 100 fb, is shown for visualization purposes. The fit (solid blue line for the total fit function, and dashed red and orange lines for its individual components) to the dimuon invariant mass distribution (right) expected in the same dimuon search bin is shown for a representative $ \mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}} $ signal (black markers) with $ m_{\mathrm{Z}_{\mathrm{D}}}= $ 5 GeV and $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}}=1 \text{cm} $. |
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Figure 11:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) $ as functions of the dark-photon mass, $ m_{\mathrm{Z}_{\mathrm{D}}} $, for $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}}= $ 0.1 (upper left), 1 (upper right), 10 (lower left), and 100$ \text{cm} $ (lower right). The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue (magenta) solid line represents the observed upper limits previously set in Ref. [18] ( [20]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. The blue (magenta) line can overlap with the gray bands, owing to the different mass ranges covered by the results from Ref. [18] ( [20]). |
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Figure 11-a:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) $ as functions of the dark-photon mass, $ m_{\mathrm{Z}_{\mathrm{D}}} $, for $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}}= $ 0.1 (upper left), 1 (upper right), 10 (lower left), and 100$ \text{cm} $ (lower right). The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue (magenta) solid line represents the observed upper limits previously set in Ref. [18] ( [20]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. The blue (magenta) line can overlap with the gray bands, owing to the different mass ranges covered by the results from Ref. [18] ( [20]). |
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Figure 11-b:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) $ as functions of the dark-photon mass, $ m_{\mathrm{Z}_{\mathrm{D}}} $, for $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}}= $ 0.1 (upper left), 1 (upper right), 10 (lower left), and 100$ \text{cm} $ (lower right). The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue (magenta) solid line represents the observed upper limits previously set in Ref. [18] ( [20]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. The blue (magenta) line can overlap with the gray bands, owing to the different mass ranges covered by the results from Ref. [18] ( [20]). |
png pdf |
Figure 11-c:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) $ as functions of the dark-photon mass, $ m_{\mathrm{Z}_{\mathrm{D}}} $, for $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}}= $ 0.1 (upper left), 1 (upper right), 10 (lower left), and 100$ \text{cm} $ (lower right). The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue (magenta) solid line represents the observed upper limits previously set in Ref. [18] ( [20]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. The blue (magenta) line can overlap with the gray bands, owing to the different mass ranges covered by the results from Ref. [18] ( [20]). |
png pdf |
Figure 11-d:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) $ as functions of the dark-photon mass, $ m_{\mathrm{Z}_{\mathrm{D}}} $, for $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}}= $ 0.1 (upper left), 1 (upper right), 10 (lower left), and 100$ \text{cm} $ (lower right). The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue (magenta) solid line represents the observed upper limits previously set in Ref. [18] ( [20]). The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. The blue (magenta) line can overlap with the gray bands, owing to the different mass ranges covered by the results from Ref. [18] ( [20]). |
png pdf |
Figure 12:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) $ as functions of $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}} $, for representative mass hypotheses, $ m_{\mathrm{Z}_{\mathrm{D}}} = $ 2 (upper left), 5 (upper right), 12 (lower left), and 20 (lower right) GeV. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue (magenta) solid line represents the observed upper limits previously set in Ref. [18] ( [20]). |
png pdf |
Figure 12-a:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) $ as functions of $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}} $, for representative mass hypotheses, $ m_{\mathrm{Z}_{\mathrm{D}}} = $ 2 (upper left), 5 (upper right), 12 (lower left), and 20 (lower right) GeV. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue (magenta) solid line represents the observed upper limits previously set in Ref. [18] ( [20]). |
png pdf |
Figure 12-b:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) $ as functions of $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}} $, for representative mass hypotheses, $ m_{\mathrm{Z}_{\mathrm{D}}} = $ 2 (upper left), 5 (upper right), 12 (lower left), and 20 (lower right) GeV. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue (magenta) solid line represents the observed upper limits previously set in Ref. [18] ( [20]). |
png pdf |
Figure 12-c:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) $ as functions of $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}} $, for representative mass hypotheses, $ m_{\mathrm{Z}_{\mathrm{D}}} = $ 2 (upper left), 5 (upper right), 12 (lower left), and 20 (lower right) GeV. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue (magenta) solid line represents the observed upper limits previously set in Ref. [18] ( [20]). |
png pdf |
Figure 12-d:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to\mathrm{Z}_{\mathrm{D}}\mathrm{Z}_{\mathrm{D}}) $ as functions of $ c\tau_{0}^{\mathrm{Z}_{\mathrm{D}}} $, for representative mass hypotheses, $ m_{\mathrm{Z}_{\mathrm{D}}} = $ 2 (upper left), 5 (upper right), 12 (lower left), and 20 (lower right) GeV. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue (magenta) solid line represents the observed upper limits previously set in Ref. [18] ( [20]). |
png pdf |
Figure 13:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to {\Psi} \bar{\Psi} ) $, for representative mass hypotheses of the Scenario A dark-shower model. Limits are shown as functions of $ c\tau_{0}^{{A}{\prime} } $, for $ m_{\tilde{\pi} } = $ 2 GeV and $ m_{{A}{\prime} } = $ 0.67 GeV (upper left), $ m_{\tilde{\pi} } = $ 5 GeV and $ m_{{A}{\prime} } = $ 1.67 GeV (upper right), and $ m_{\tilde{\pi} } = $ 7.5 GeV and $ m_{{A}{\prime} } = $ 2.5 GeV (lower). For this model, it is assumed $ \tilde{\Lambda} = m_{\tilde{\eta} } = 4m_{\tilde{\pi} } $, $ \sin\theta = $ 0.1 and $ \mathcal{B}(\tilde{\pi} _3 \to {A}{\prime} {A}{\prime} )= $ 1. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue solid line represents the observed upper limits previously set in Ref. [21], rescaled to the same Higgs boson production cross section of 59.8 pb [38,39]. |
png pdf |
Figure 13-a:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to {\Psi} \bar{\Psi} ) $, for representative mass hypotheses of the Scenario A dark-shower model. Limits are shown as functions of $ c\tau_{0}^{{A}{\prime} } $, for $ m_{\tilde{\pi} } = $ 2 GeV and $ m_{{A}{\prime} } = $ 0.67 GeV (upper left), $ m_{\tilde{\pi} } = $ 5 GeV and $ m_{{A}{\prime} } = $ 1.67 GeV (upper right), and $ m_{\tilde{\pi} } = $ 7.5 GeV and $ m_{{A}{\prime} } = $ 2.5 GeV (lower). For this model, it is assumed $ \tilde{\Lambda} = m_{\tilde{\eta} } = 4m_{\tilde{\pi} } $, $ \sin\theta = $ 0.1 and $ \mathcal{B}(\tilde{\pi} _3 \to {A}{\prime} {A}{\prime} )= $ 1. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue solid line represents the observed upper limits previously set in Ref. [21], rescaled to the same Higgs boson production cross section of 59.8 pb [38,39]. |
png pdf |
Figure 13-b:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to {\Psi} \bar{\Psi} ) $, for representative mass hypotheses of the Scenario A dark-shower model. Limits are shown as functions of $ c\tau_{0}^{{A}{\prime} } $, for $ m_{\tilde{\pi} } = $ 2 GeV and $ m_{{A}{\prime} } = $ 0.67 GeV (upper left), $ m_{\tilde{\pi} } = $ 5 GeV and $ m_{{A}{\prime} } = $ 1.67 GeV (upper right), and $ m_{\tilde{\pi} } = $ 7.5 GeV and $ m_{{A}{\prime} } = $ 2.5 GeV (lower). For this model, it is assumed $ \tilde{\Lambda} = m_{\tilde{\eta} } = 4m_{\tilde{\pi} } $, $ \sin\theta = $ 0.1 and $ \mathcal{B}(\tilde{\pi} _3 \to {A}{\prime} {A}{\prime} )= $ 1. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue solid line represents the observed upper limits previously set in Ref. [21], rescaled to the same Higgs boson production cross section of 59.8 pb [38,39]. |
png pdf |
Figure 13-c:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to {\Psi} \bar{\Psi} ) $, for representative mass hypotheses of the Scenario A dark-shower model. Limits are shown as functions of $ c\tau_{0}^{{A}{\prime} } $, for $ m_{\tilde{\pi} } = $ 2 GeV and $ m_{{A}{\prime} } = $ 0.67 GeV (upper left), $ m_{\tilde{\pi} } = $ 5 GeV and $ m_{{A}{\prime} } = $ 1.67 GeV (upper right), and $ m_{\tilde{\pi} } = $ 7.5 GeV and $ m_{{A}{\prime} } = $ 2.5 GeV (lower). For this model, it is assumed $ \tilde{\Lambda} = m_{\tilde{\eta} } = 4m_{\tilde{\pi} } $, $ \sin\theta = $ 0.1 and $ \mathcal{B}(\tilde{\pi} _3 \to {A}{\prime} {A}{\prime} )= $ 1. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue solid line represents the observed upper limits previously set in Ref. [21], rescaled to the same Higgs boson production cross section of 59.8 pb [38,39]. |
png pdf |
Figure 14:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to {\Psi} \bar{\Psi} ) $, for representative mass hypotheses of the Scenario B1 dark-shower model. Limits are shown as functions of $ c\tau_{0}^{{A}{\prime} } $, for $ m_{\tilde{\pi} } = $ 2 GeV and $ m_{{A}{\prime} } = $ 0.67 GeV (upper left), $ m_{\tilde{\pi} } = $ 5 GeV and $ m_{{A}{\prime} } = $ 1.67 GeV (upper right), and $ m_{\tilde{\pi} } = $ 7.5 GeV and $ m_{{A}{\prime} } = $ 2.5 GeV (lower). For this model, it is assumed $ \tilde{\Lambda} = m_{\tilde{\eta} } = 4m_{\tilde{\pi} } $, $ \sin\theta = $ 0.1 and $ \mathcal{B}(\tilde{\pi} _3 \to {A}{\prime} {A}{\prime} )= $ 1. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue solid line represents the observed upper limits previously set in Ref. [21], rescaled to the same Higgs boson production cross section of 59.8 pb [38,39]. |
png pdf |
Figure 14-a:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to {\Psi} \bar{\Psi} ) $, for representative mass hypotheses of the Scenario B1 dark-shower model. Limits are shown as functions of $ c\tau_{0}^{{A}{\prime} } $, for $ m_{\tilde{\pi} } = $ 2 GeV and $ m_{{A}{\prime} } = $ 0.67 GeV (upper left), $ m_{\tilde{\pi} } = $ 5 GeV and $ m_{{A}{\prime} } = $ 1.67 GeV (upper right), and $ m_{\tilde{\pi} } = $ 7.5 GeV and $ m_{{A}{\prime} } = $ 2.5 GeV (lower). For this model, it is assumed $ \tilde{\Lambda} = m_{\tilde{\eta} } = 4m_{\tilde{\pi} } $, $ \sin\theta = $ 0.1 and $ \mathcal{B}(\tilde{\pi} _3 \to {A}{\prime} {A}{\prime} )= $ 1. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue solid line represents the observed upper limits previously set in Ref. [21], rescaled to the same Higgs boson production cross section of 59.8 pb [38,39]. |
png pdf |
Figure 14-b:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to {\Psi} \bar{\Psi} ) $, for representative mass hypotheses of the Scenario B1 dark-shower model. Limits are shown as functions of $ c\tau_{0}^{{A}{\prime} } $, for $ m_{\tilde{\pi} } = $ 2 GeV and $ m_{{A}{\prime} } = $ 0.67 GeV (upper left), $ m_{\tilde{\pi} } = $ 5 GeV and $ m_{{A}{\prime} } = $ 1.67 GeV (upper right), and $ m_{\tilde{\pi} } = $ 7.5 GeV and $ m_{{A}{\prime} } = $ 2.5 GeV (lower). For this model, it is assumed $ \tilde{\Lambda} = m_{\tilde{\eta} } = 4m_{\tilde{\pi} } $, $ \sin\theta = $ 0.1 and $ \mathcal{B}(\tilde{\pi} _3 \to {A}{\prime} {A}{\prime} )= $ 1. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue solid line represents the observed upper limits previously set in Ref. [21], rescaled to the same Higgs boson production cross section of 59.8 pb [38,39]. |
png pdf |
Figure 14-c:
Upper limits at 95% CL on the branching fraction $ \mathcal{B}(\mathrm{H}\to {\Psi} \bar{\Psi} ) $, for representative mass hypotheses of the Scenario B1 dark-shower model. Limits are shown as functions of $ c\tau_{0}^{{A}{\prime} } $, for $ m_{\tilde{\pi} } = $ 2 GeV and $ m_{{A}{\prime} } = $ 0.67 GeV (upper left), $ m_{\tilde{\pi} } = $ 5 GeV and $ m_{{A}{\prime} } = $ 1.67 GeV (upper right), and $ m_{\tilde{\pi} } = $ 7.5 GeV and $ m_{{A}{\prime} } = $ 2.5 GeV (lower). For this model, it is assumed $ \tilde{\Lambda} = m_{\tilde{\eta} } = 4m_{\tilde{\pi} } $, $ \sin\theta = $ 0.1 and $ \mathcal{B}(\tilde{\pi} _3 \to {A}{\prime} {A}{\prime} )= $ 1. The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all event categories. The dark blue solid line represents the observed upper limits previously set in Ref. [21], rescaled to the same Higgs boson production cross section of 59.8 pb [38,39]. |
png pdf |
Figure 15:
Upper limits at 95% CL on the branching fraction product $ \mathcal{B}(\mathrm{h}_\mathrm{b} \to \phi X)\mathcal{B}(\phi\to\mu\mu) $ as functions of the long-lived scalar resonance mass, $ m_{\phi} $, for $ c\tau_{0}^{\phi}= $ 0.1 (upper left), 1 (upper right), and 10$ \text{cm} $ (lower). The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all dimuon event categories. The dark blue solid line represents the exclusion limits previously set in Ref. [18]. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. The blue line can overlap with the gray bands, owing to the different mass ranges covered by the results from Ref. [18]. |
png pdf |
Figure 15-a:
Upper limits at 95% CL on the branching fraction product $ \mathcal{B}(\mathrm{h}_\mathrm{b} \to \phi X)\mathcal{B}(\phi\to\mu\mu) $ as functions of the long-lived scalar resonance mass, $ m_{\phi} $, for $ c\tau_{0}^{\phi}= $ 0.1 (upper left), 1 (upper right), and 10$ \text{cm} $ (lower). The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all dimuon event categories. The dark blue solid line represents the exclusion limits previously set in Ref. [18]. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. The blue line can overlap with the gray bands, owing to the different mass ranges covered by the results from Ref. [18]. |
png pdf |
Figure 15-b:
Upper limits at 95% CL on the branching fraction product $ \mathcal{B}(\mathrm{h}_\mathrm{b} \to \phi X)\mathcal{B}(\phi\to\mu\mu) $ as functions of the long-lived scalar resonance mass, $ m_{\phi} $, for $ c\tau_{0}^{\phi}= $ 0.1 (upper left), 1 (upper right), and 10$ \text{cm} $ (lower). The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all dimuon event categories. The dark blue solid line represents the exclusion limits previously set in Ref. [18]. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. The blue line can overlap with the gray bands, owing to the different mass ranges covered by the results from Ref. [18]. |
png pdf |
Figure 15-c:
Upper limits at 95% CL on the branching fraction product $ \mathcal{B}(\mathrm{h}_\mathrm{b} \to \phi X)\mathcal{B}(\phi\to\mu\mu) $ as functions of the long-lived scalar resonance mass, $ m_{\phi} $, for $ c\tau_{0}^{\phi}= $ 0.1 (upper left), 1 (upper right), and 10$ \text{cm} $ (lower). The solid black (dashed black) line represents the observed (median expected) exclusion. The inner blue (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis. The limits are obtained using the combination of all dimuon event categories. The dark blue solid line represents the exclusion limits previously set in Ref. [18]. The vertical gray bands indicate mass ranges containing known SM resonances, which are masked for the purpose of this search. The blue line can overlap with the gray bands, owing to the different mass ranges covered by the results from Ref. [18]. |
| Tables | |
png pdf |
Table 1:
List of known SM resonances and corresponding masked mass windows, equal to $ \pm5\sigma_{\text{mass}} $ around the mean mass, where mean and resolution ($ \sigma_{\text{mass}} $) are determined from a fit to data. |
| Summary |
| A search for displaced multimuon resonances has been performed using proton-proton collisions at a center-of-mass energy of 13.6 TeV, collected by the CMS experiment at the LHC in 2022 and 2023, corresponding to an integrated luminosity of 62.4 fb$^{-1}$. The data were collected using a dedicated dimuon trigger stream with low transverse momentum thresholds, recorded at high rate by retaining a reduced amount of information at the high-level trigger, to explore otherwise inaccessible phase space at low multimuon invariant mass and nonzero displacement from the primary interaction vertex. No significant excess above the standard model prediction is found. The data are used to set constraints on a wide range of mass and lifetime hypotheses for various scenarios of physics beyond the standard model. Three sets of models are considered: the hidden Abelian Higgs model, where the Higgs boson decays into a pair of long-lived dark photons; dark-shower models, where dark showers originate from the Higgs boson decays into dark quarks; and models where a long-lived scalar resonance is produced from the decay of a b hadron. In models with a b hadron, the improved trigger and analysis strategy compensate for the smaller data set, leading to constraints comparable with the previous results. For other models, the constraints obtained are instead the most stringent to date in a large fraction of the explored parameter space. In the hidden Abelian Higgs model, the most stringent limits to date are obtained for dark-photon proper decay lengths greater than 1$ \text{cm} $ and dark-photon masses less than 5 GeV. In the dark-shower models, the most stringent limits to date are set for proper decay lengths larger than 10$ \text{cm} $. |
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