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| CMS-EXO-21-005 ; CERN-EP-2023-165 | ||
| Search for direct production of GeV-scale resonances decaying to a pair of muons in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 28 September 2023 | ||
| JHEP 12 (2023) 070 | ||
| Abstract: A search for direct production of low-mass dimuon resonances is performed using $ \sqrt{s}= $ 13 TeV proton-proton collision data collected by the CMS experiment during the 2017-2018 operation of the CERN LHC with an integrated luminosity of 96.6 fb$^{-1}$. The search exploits a dedicated high-rate trigger stream that records events with two muons with transverse momenta as low as 3 GeV but does not include the full event information. The search is performed by looking for narrow peaks in the dimuon mass spectrum in the ranges of 1.1-2.6 GeV and 4.2-7.9 GeV. No significant excess of events above the expectation from the standard model background is observed. Model-independent limits on production rates of dimuon resonances within the experimental fiducial acceptance are set. Competitive or world's best limits are set at 90% confidence level for a minimal dark photon model and for a scenario with two Higgs doublets and an extra complex scalar singlet (2HDM+S). Values of the squared kinetic mixing coefficient $ \varepsilon^2 $ in the dark photon model above 10$^{-6} $ are excluded over most of the mass range of the search. In the 2HDM+S, values of the mixing angle $ \sin(\theta_{\mathrm{H}}) $ above 0.08 are excluded over most of the mass range of the search with a fixed ratio of the Higgs doublets vacuum expectation $ \tan\beta= $ 0.5. | ||
| Links: e-print arXiv:2309.16003 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; Physics Briefing ; CADI line (restricted) ; | ||
| Figures & Tables | Summary | Additional Figures & Tables | References | CMS Publications |
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| Figures | |
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Figure 1:
Expected dominant production modes for a dark photon $ \mathrm{Z}_{\mathrm{D}} $ (left) and light beyond-SM pseudoscalar boson $\mathrm{a}$ (right). |
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Figure 1-a:
Expected dominant production mode for a dark photon $ \mathrm{Z}_{\mathrm{D}} $. |
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Figure 1-b:
Expected dominant production mode for a light beyond-SM pseudoscalar boson $\mathrm{a}$. |
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Figure 2:
The measured 2017 (left) and 2018 (right) efficiencies of the dimuon scouting trigger and logical OR of all L1 triggers using 2017-2018 data. Each cell value represents the probability that a pair of muons meeting the trigger requirements will activate the dimuon scouting trigger. The $ x $-axis shows the dimuon mass and includes the entire relevant range for this analysis. The $ y $-axis shows the angular separation, $ \Delta R $, between the two muons. Statistical uncertainty on the value of each cell is less than 5%. |
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Figure 2-a:
The measured 2017 efficiency of the dimuon scouting trigger and logical OR of all L1 triggers using 2017-2018 data. Each cell value represents the probability that a pair of muons meeting the trigger requirements will activate the dimuon scouting trigger. The $ x $-axis shows the dimuon mass and includes the entire relevant range for this analysis. The $ y $-axis shows the angular separation, $ \Delta R $, between the two muons. Statistical uncertainty on the value of each cell is less than 5%. |
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Figure 2-b:
The measured 2018 efficiency of the dimuon scouting trigger and logical OR of all L1 triggers using 2017-2018 data. Each cell value represents the probability that a pair of muons meeting the trigger requirements will activate the dimuon scouting trigger. The $ x $-axis shows the dimuon mass and includes the entire relevant range for this analysis. The $ y $-axis shows the angular separation, $ \Delta R $, between the two muons. Statistical uncertainty on the value of each cell is less than 5%. |
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Figure 3:
The $ m_{\mu\mu} $ distribution obtained with the muon scouting data collected during 2017-2018 with two sets of selections: the $ \Upsilon{\textrm{(1S)}} $-trained muon MVA identification with $ L_{\mathrm{xy}} < $ 0.015 cm (blue, solid), and the J$/ \psi $-trained muon MVA identification with $ L_{\mathrm{xy}}/{\sigma}_{L_{\mathrm{xy}}} < $ 3.5 (red, dashed). |
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Figure 4:
The signal acceptance and reconstruction efficiency are extracted from the dark photon (purple, dark) and pseudoscalar (cyan, light) simulations. The region at 2.6-4.2 GeV is excluded because of the presence of the J$/ \psi $ and $ \psi $(2S) resonances. |
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Figure 5:
Left: Expected and observed model-independent upper limits at 95% CL on the product of the signal cross section ($ \sigma $), the branching fraction to a pair of muons for the inclusive dimuon selection ($ \mathcal{B} $), and fiducial acceptance ($ A $). Right: The model-independent limits for the high-$ p_{\mathrm{T}} $ selection. The mass region dominated by the J$/ \psi $ and $ \psi $(2S) resonances is excluded from the search. |
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Figure 5-a:
Expected and observed model-independent upper limits at 95% CL on the product of the signal cross section ($ \sigma $), the branching fraction to a pair of muons for the inclusive dimuon selection ($ \mathcal{B} $), and fiducial acceptance ($ A $). |
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Figure 5-b:
The model-independent limits for the high-$ p_{\mathrm{T}} $ selection. The mass region dominated by the J$/ \psi $ and $ \psi $(2S) resonances is excluded from the search. |
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Figure 6:
Observed upper limits at 90% CL on the square of the kinetic mixing coefficient $ \varepsilon $ in the minimal model of a dark photon from the CMS search in the mass ranges of 1.1-2.6 GeV and 4.2-7.9 GeV (pink). The CMS limits are compared with the existing limits at 90% CL provided by LHCb [13] (blue) and BaBar [11] (gray). |
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Figure 7:
Observed upper limits at 90% CL on the mixing angle $ \theta_{\mathrm{H}} $ for the 2HDM+S scenario from the CMS search in the mass ranges of 1.1-2.6 GeV and 4.2-7.9 GeV (pink). The CMS limits are compared with the existing limits at 90% CL provided by LHCb [20] (blue) and BaBar [11] (gray). |
| Tables | |
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Table 1:
The set of dimuon L1 requirements applied in the high-rate triggers. |
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Table 2:
Summary of all selection criteria for an event to enter the analysis in inclusive and high-$ p_{\mathrm{T}} $ search categories. |
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Table 3:
Summary of the experimental systematic uncertainties for a signal model in the model independent search for a dimuon resonance. |
| Summary |
| A search for direct production of a narrow resonance decaying to a pair of muons has been presented using proton-proton collision data recorded by the CMS experiment at $ \sqrt{s}= $ 13 TeV in 2017-2018. The search is performed in the dimuon mass regions of 1.1-2.6 GeV and 4.2-7.9 GeV using data collected in a dedicated high-rate trigger stream, corresponding to an integrated luminosity of 96.6 fb$ ^{-1} $. A multivariate analysis method is used to identify muons to achieve a higher sensitivity. No significant excess of events above the expectation from the standard model background is observed. Model-independent limits on production rates of dimuon resonances within the experimental fiducial acceptance are set. Competitive or world's best limits are set at 90% confidence level for a minimal dark photon model and for a scenario with two Higgs doublets and an extra complex scalar singlet (2HDM+S). Values of the squared kinetic mixing coefficient $ \varepsilon^2 $ in the dark photon model above 10$^{-6} $ are excluded over most of the mass range of the search. In the 2HDM+S, values of the mixing angle $ \sin(\theta_{\mathrm{H}}) $ above 0.08 are excluded over most of the mass range of the search with a fixed ratio of the Higgs doublets vacuum expectation $ \tan\beta= $ 0.5. |
| Additional Figures | |
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Additional Figure 1:
Upper limits at 90% CL on the square of the kinetic mixing coefficient $ \varepsilon $ in the minimal model of a dark photon from the CMS search in the mass ranges of 1.1-2.6 GeV and 4.2-7.9 GeV using 2017 and 2018 scouting data which corresponds to an integrated luminosity of 96.6 fb$ ^{-1} $. The theoretical uncertainty includes the variation of QCD scales when calculating the production cross section, as well as the variance in fiducial acceptance between dark photon signal events produced using two different generators; DYTURBO and MADGRAPH 5_aMC@NLO v3.4.1. |
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Additional Figure 2:
Upper limits at 90% CL on the mixing angle $ \theta_{\rm H} $ for the 2HDM+S scenario the CMS search in the mass ranges of 1.1-2.6 GeV and 4.2-7.9 GeV using 2017 and 2018 scouting data which corresponds to an integrated luminosity of 96.6 fb$ ^{-1} $. The theoretical uncertainty includes the variation of QCD scales when calculating the production cross section, as well as the variance in fiducial acceptance between scalar signal events produced using two different generators; PYTHIA 8.230 and MADGRAPH 5_aMC@NLO v3.4.1. |
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Additional Figure 3:
Background only and signal plus background fits, for the mass window 2.25-2.56 GeV with 2.58$ \sigma $ excess in 2017 (top) and 2018 (bottom). This excess is observed only in the mass distribution with the dimuon high-$ p_{\mathrm{T}} $ selection and therefore only affects the limit on the scalar model. The lower pads show the difference between the data and corresponding pdf, divided by the statistical uncertainty of the data in that bin. |
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Additional Figure 3-a:
Background only and signal plus background fits, for the mass window 2.25-2.56 GeV in 2017. The lower pad shows the difference between the data and corresponding pdf, divided by the statistical uncertainty of the data in that bin. |
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Additional Figure 3-b:
Background only and signal plus background fits, for the mass window 2.25-2.56 GeV in 2018. The lower pad shows the difference between the data and corresponding pdf, divided by the statistical uncertainty of the data in that bin. |
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Additional Figure 4:
The combined efficiency of the dimuon scouting trigger and the MVA muon selection, averaged between 2017 and 2018, weighted by the integrated luminosity of each year. The solid line shows the efficiency of the inclusive selection used for the limit on the dark photon model. The dashed line shows the efficiency of the high-$ p_{\mathrm{T}} $ selection optimized for the scalar model. |
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Additional Figure 5:
Theory cross-section times branching fraction to muons times acceptance for the dark photon and 2HDM+S models. The dark photon theory cross section is calculated using MADGRAPH 5_aMC@NLO v3.4.1 assuming $ \varepsilon = $ 0.02, and the acceptance is derived using DYTURBO. The 2HDM+S model theory cross section is calculated using HIGLU at NNLO assuming $ \sin(\theta_{\rm H}) = $ 1, and the acceptance is derived from PYTHIA 8.230. |
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Additional Figure 6:
The contribution of $ \mathrm{D^0}\to \mathrm{K^+}\mathrm{K^-} $ in the simultaneous fit in signal region (left) and control regions (right) in 2018 data for the inclusive dimuon selection. The background contains non-peaking combinatorial background and $ \mathrm{D^0}\to \mathrm{K^+}\mathrm{K^-} $ background. In the bottom panel, the combinatorial background component in the signal plus background fit is subtracted from the observed data (``Data - Comb. Bkg.''). |
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Additional Figure 6-a:
The contribution of $ \mathrm{D^0}\to \mathrm{K^+}\mathrm{K^-} $ in the simultaneous fit in the signal region in 2018 data for the inclusive dimuon selection. The background contains non-peaking combinatorial background and $ \mathrm{D^0}\to \mathrm{K^+}\mathrm{K^-} $ background. In the bottom panel, the combinatorial background component in the signal plus background fit is subtracted from the observed data (``Data - Comb. Bkg.''). |
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Additional Figure 6-b:
The contribution of $ \mathrm{D^0}\to \mathrm{K^+}\mathrm{K^-} $ in the simultaneous fit in the control region in 2018 data for the inclusive dimuon selection. The background contains non-peaking combinatorial background and $ \mathrm{D^0}\to \mathrm{K^+}\mathrm{K^-} $ background. In the bottom panel, the combinatorial background component in the signal plus background fit is subtracted from the observed data (``Data - Comb. Bkg.''). |
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Additional Figure 7:
The contribution of $ \mathrm{D^0}\to\mathrm{K^-}\pi^{+} $ in the simultaneous fit in signal region (left) and control regions (right) in 2018 data for the inclusive dimuon selection. The background contains non-peaking combinatorial background and $ \mathrm{D^0}\to\mathrm{K^-}\pi^{+} $ background. In the bottom panel, the combinatorial background component in the signal plus background fit is subtracted from the observed data (``Data - Comb. Bkg.''). |
png pdf |
Additional Figure 7-a:
The contribution of $ \mathrm{D^0}\to\mathrm{K^-}\pi^{+} $ in the simultaneous fit in the signal region in 2018 data for the inclusive dimuon selection. The background contains non-peaking combinatorial background and $ \mathrm{D^0}\to\mathrm{K^-}\pi^{+} $ background. In the bottom panel, the combinatorial background component in the signal plus background fit is subtracted from the observed data (``Data - Comb. Bkg.''). |
png pdf |
Additional Figure 7-b:
The contribution of $ \mathrm{D^0}\to\mathrm{K^-}\pi^{+} $ in the simultaneous fit in the control region in 2018 data for the inclusive dimuon selection. The background contains non-peaking combinatorial background and $ \mathrm{D^0}\to\mathrm{K^-}\pi^{+} $ background. In the bottom panel, the combinatorial background component in the signal plus background fit is subtracted from the observed data (``Data - Comb. Bkg.''). |
png pdf |
Additional Figure 8:
The observed local p-value for the inclusive dimuon selection (left) and high-$ p_{\mathrm{T}} $ selection (right). The mass region dominated by the J$/ \psi $ and $\psi$(2S) resonances is excluded from the search. |
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Additional Figure 8-a:
The observed local p-value for the inclusive dimuon selection. The mass region dominated by the J$/ \psi $ and $\psi$(2S) resonances is excluded from the search. |
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Additional Figure 8-b:
The observed local p-value for the high-$ p_{\mathrm{T}} $ selection. The mass region dominated by the J$/ \psi $ and $\psi$(2S) resonances is excluded from the search. |
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Additional Figure 9:
The ROC curves of J/$ \psi $-trained and $ \Upsilon $-trained muon MVA identification in comparison to the cut-based identification used in the previous CMS dark photon search. |
| Additional Tables | |
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Additional Table 1:
The fiducial space for the signal acceptance. |
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Compact Muon Solenoid LHC, CERN |
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