Search for low-mass hidden-valley dark showers with non-prompt muon pairs in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The CMS collaboration
CMS-EXO-24-008, 2025.

Abstract (data 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 $41.6~\textrm{fb}^{-1}$, which was collected in proton-proton collisions at $\sqrt{s}=13~\textrm{TeV}$ 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 $500~\textrm{mm}$ and for $\tilde{\omega}$ masses down to $0.3~\textrm{GeV}$. First limits are set for extended dark-shower models with two dark flavours that contain dark photons, probing their masses down to $0.33~\textrm{GeV}$.

  • Scenario A dimuon mass distribution at 0.67 GeV

    Figure 7a

    10.17182/hepdata.165888.v1/t1

    Dimuon invariant mass distributions in mass windows around $0.67~\textrm{GeV}$ in the single-vertex category with $1~\textrm{cm}<l_{xy}<10~\textrm{cm}$ and $\textrm{pointing angle}<0.2$. The background...

  • Scenario B1 dimuon mass distribution at 1.33 GeV

    Figure 7b

    10.17182/hepdata.165888.v1/t2

    Dimuon invariant mass distributions in mass windows around $1.33~\textrm{GeV}$ in the single-vertex category with $1~\textrm{cm}<l_{xy}<10~\textrm{cm}$ and $\textrm{pointing angle}<0.2$. The background...

  • Vector portal limits, $m_{\tilde{\omega}}=2$GeV

    Figure 8a

    10.17182/hepdata.165888.v1/t3

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\omega}$ meson $c\tau$ for $m_{\tilde{\omega}}=2~\textrm{GeV}$...

  • Vector portal limits, $m_{\tilde{\omega}}=5$GeV

    Figure 8b

    10.17182/hepdata.165888.v1/t4

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\omega}$ meson $c\tau$ for $m_{\tilde{\omega}}=5~\textrm{GeV}$...

  • Vector portal limits, $m_{\tilde{\omega}}=15$GeV

    Figure 8c

    10.17182/hepdata.165888.v1/t5

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\omega}$ meson $c\tau$ for $m_{\tilde{\omega}}=15~\textrm{GeV}$...

  • Vector portal limits, $m_{\tilde{\omega}}=20$GeV

    Figure 8d

    10.17182/hepdata.165888.v1/t6

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\omega}$ meson $c\tau$ for $m_{\tilde{\omega}}=20~\textrm{GeV}$...

  • Scenario A limits, $m_{A'}=0.33$ GeV

    Figure 9a

    10.17182/hepdata.165888.v1/t7

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\textrm{A}'$ $c\tau$ for $m_{\tilde{\pi}_{3}}=1~\textrm{GeV}$ and...

  • Scenario A limits, $m_{A'}=0.4$ GeV

    Figure 9b

    10.17182/hepdata.165888.v1/t8

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\textrm{A}'$ $c\tau$ for $m_{\tilde{\pi}_{3}}=4~\textrm{GeV}$ and...

  • Scenario A limits, $m_{A'}=0.67$ GeV

    Figure 9c

    10.17182/hepdata.165888.v1/t9

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\textrm{A}'$ $c\tau$ for $m_{\tilde{\pi}_{3}}=2~\textrm{GeV}$ and...

  • Scenario A limits, $m_{A'}=1.33$ GeV

    Figure 9d

    10.17182/hepdata.165888.v1/t10

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\textrm{A}'$ $c\tau$ for $m_{\tilde{\pi}_{3}}=4~\textrm{GeV}$ and...

  • Scenario B1 limits, $m_{A'}=0.33$ GeV

    Figure 10a

    10.17182/hepdata.165888.v1/t11

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\pi}_{3}$ meson $c\tau$ for $m_{\tilde{\pi}_{3}}=1~\textrm{GeV}$...

  • Scenario B1 limits, $m_{A'}=0.4$ GeV

    Figure 10b

    10.17182/hepdata.165888.v1/t12

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\pi}_{3}$ meson $c\tau$ for $m_{\tilde{\pi}_{3}}=2~\textrm{GeV}$...

  • Scenario B1 limits, $m_{A'}=0.67$ GeV

    Figure 10c

    10.17182/hepdata.165888.v1/t13

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\pi}_{3}$ meson $c\tau$ for $m_{\tilde{\pi}_{3}}=2~\textrm{GeV}$...

  • Scenario B1 limits, $m_{A'}=1.33$ GeV

    Figure 10d

    10.17182/hepdata.165888.v1/t14

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\pi}_{3}$ meson $c\tau$ for $m_{\tilde{\pi}_{3}}=4~\textrm{GeV}$...

  • Vector portal limits, $c\tau=10$mm

    Figure 11a

    10.17182/hepdata.165888.v1/t15

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\omega}$ meson mass for $c\tau=10~\textrm{mm}$...

  • Vector portal limits, $c\tau=100$mm

    Figure 11b

    10.17182/hepdata.165888.v1/t16

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\omega}$ meson mass for $c\tau=100~\textrm{mm}$...

  • Scenario A limits, $m_{\tilde{\pi}_{3}}=10m_{A'}$, $c\tau=10$mm

    Figure 12a

    10.17182/hepdata.165888.v1/t17

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\to\psi\overline{\psi}\right)$ as a function of the $\mathrm{A}'$ mass in Scenario A,...

  • Scenario A limits, $m_{\tilde{\pi}_{3}}=3m_{A'}$, $c\tau=10$mm

    Figure 12b

    10.17182/hepdata.165888.v1/t18

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\to\psi\overline{\psi}\right)$ as a function of the $\mathrm{A}'$ mass in Scenario A,...

  • Scenario A limits, $m_{\tilde{\pi}_{3}}=10m_{A'}$, $c\tau=100$mm

    Figure 12c

    10.17182/hepdata.165888.v1/t19

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\to\psi\overline{\psi}\right)$ as a function of the $\mathrm{A}'$ mass in Scenario A,...

  • Scenario A limits, $m_{\tilde{\pi}_{3}}=3m_{A'}$, $c\tau=100$mm

    Figure 12d

    10.17182/hepdata.165888.v1/t20

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\to\psi\overline{\psi}\right)$ as a function of the $\mathrm{A}'$ mass in Scenario A,...

  • Scenario B1 limits, $m_{\tilde{\pi}_{3}}=10m_{A'}$, $c\tau=10$mm

    Figure 13a

    10.17182/hepdata.165888.v1/t21

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\to\psi\overline{\psi}\right)$ as a function of the $\mathrm{A}'$ mass in Scenario B1,...

  • Scenario B1 limits, $m_{\tilde{\pi}_{3}}=3m_{A'}$, $c\tau=10$mm

    Figure 13b

    10.17182/hepdata.165888.v1/t22

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\to\psi\overline{\psi}\right)$ as a function of the $\mathrm{A}'$ mass in Scenario B1,...

  • Scenario B1 limits, $m_{\tilde{\pi}_{3}}=10m_{A'}$,$c\tau=100$mm

    Figure 13c

    10.17182/hepdata.165888.v1/t23

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\to\psi\overline{\psi}\right)$ as a function of the $\mathrm{A}'$ mass in Scenario B1,...

  • Scenario B1 limits, $m_{\tilde{\pi}_{3}}=3m_{A'}$,$c\tau=100$mm

    Figure 13d

    10.17182/hepdata.165888.v1/t24

    Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\to\psi\overline{\psi}\right)$ as a function of the $\mathrm{A}'$ mass in Scenario B1,...

  • Vector portal 2D limits

    Figure 14

    10.17182/hepdata.165888.v1/t25

    Observed upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\omega}$ meson mass and...

  • Scenario A 2D limits, $m_{\tilde{\pi}_{3}}=10m_{A'}$

    Figure 15a

    10.17182/hepdata.165888.v1/t26

    Observed upper limits at $95\%$ CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as functions of the $\textrm{A}'$ mass and $c\tau$ for...

  • Scenario A 2D limits, $m_{\tilde{\pi}_{3}}=3m_{A'}$

    Figure 15b

    10.17182/hepdata.165888.v1/t27

    Observed upper limits at $95\%$ CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as functions of the $\textrm{A}'$ mass and $c\tau$ for...

  • Scenario B1 2D limits, $m_{\tilde{\pi}_{3}}=10m_{A'}$

    Figure 16a

    10.17182/hepdata.165888.v1/t28

    Observed upper limits at $95\%$ CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as functions of the $\textrm{A}'$ mass and $c\tau$ for...

  • Scenario B1 2D limits, $m_{\tilde{\pi}_{3}}=3m_{A'}$

    Figure 16b

    10.17182/hepdata.165888.v1/t29

    Observed upper limits at $95\%$ CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as functions of the $\textrm{A}'$ mass and $c\tau$ for...

  • Vector portal cutflow efficiencies

    Example location

    10.17182/hepdata.165888.v1/t30

    Cutflow efficiencies for representative signal model points in the vector portal.

  • Scenario A cutflow efficiencies

    Example location

    10.17182/hepdata.165888.v1/t31

    Cutflow efficiencies for representative signal model points in Scenario A.

  • Scenario B1 cutflow efficiencies

    Example location

    10.17182/hepdata.165888.v1/t32

    Cutflow efficiencies for representative signal model points in Scenario B1.

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