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Search for resonant production of strongly coupled dark matter in proton-proton collisions at 13 TeV

The collaboration
CMS-EXO-19-020, 2021.

Abstract (data abstract)
The first collider search for dark matter arising from a strongly coupled hidden sector is presented, using a data sample corresponding to $138\,\text{fb}^{-1}$, collected with the CMS detector at the CERN LHC, at a center-of-mass energy of $13\,\text{TeV}$. The hidden sector is hypothesized to couple to the standard model (SM) via a heavy leptophobic $\text{Z}^{\prime}$ mediator, which would be produced as a resonance in proton-proton collisions. The mediator decay results in two "semivisible" jets, containing both visible matter and invisible dark matter. The final state therefore includes moderate missing energy aligned with one of the jets, a signature ignored by most dark matter searches. The observed dijet transverse mass spectra are smoothly falling, as expected from the SM; no structure compatible with the signal is observed. Assuming the $\text{Z}^{\prime}$ and SM Z bosons have the same couplings to the SM quarks, an inclusive search, relevant to any model that exhibits this kinematic behavior, excludes mediator masses of 1.5--$4.0\,\text{TeV}$ at 95% confidence level, depending on the other signal model parameters. To enhance the sensitivity of the search for this particular class of hidden sector models, a boosted decision tree (BDT) is trained using jet substructure variables to distinguish between semivisible jets and SM jets from background processes. When the BDT is employed to identify each jet in the dijet system as semivisible, the mediator mass exclusion increases to $5.1\,\text{TeV}$, for wider ranges of the other signal model parameters.

• Figure 2a

Data from Figure 2 (left).

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The normalized distribution of the characteristic variable $R_{\text{T}}$ for the simulated SM backgrounds and several signal models. The requirement on...

• Figure 2b

Data from Figure 2 (right).

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The normalized distribution of the characteristic variable $\Delta\phi_{\text{min}}$ for the simulated SM backgrounds and several signal models. The requirement on...

• Figure 3a

Data from Figure 3 (left).

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The normalized distributions of the BDT input variable $m_{\text{SD}}$ for the two highest $p_{\text{T}}$ jets from the simulated SM backgrounds...

• Figure 3b

Data from Figure 3 (right).

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The normalized distributions of the BDT input variable $D_{p_{\text{T}}}$ for the two highest $p_{\text{T}}$ jets from the simulated SM backgrounds...

• Figure 4a

Data from Figure 4 (left).

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The normalized BDT discriminator distribution for the two highest $p_{\text{T}}$ jets from the simulated SM backgrounds and several signal models.

• Figure 4b (signal vs. QCD)

Data from Figure 4 (right).

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The BDT ROC curves for the two highest $p_{\text{T}}$ jets, comparing the simulated SM backgrounds with one signal model with...

• Figure 4b (signal vs. $\text{t}\overline{\text{t}}$)

Data from Figure 4 (right).

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The BDT ROC curves for the two highest $p_{\text{T}}$ jets, comparing the simulated SM backgrounds with one signal model with...

• Figure 4b (signal vs. W+jets)

Data from Figure 4 (right).

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The BDT ROC curves for the two highest $p_{\text{T}}$ jets, comparing the simulated SM backgrounds with one signal model with...

• Figure 4b (signal vs. Z+jets)

Data from Figure 4 (right).

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The BDT ROC curves for the two highest $p_{\text{T}}$ jets, comparing the simulated SM backgrounds with one signal model with...

• Figure 5a

Data from Figure 5 (left).

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The $m_{\text{T}}$ distribution for the high-$R_{\text{T}}$ signal region, comparing the observed data to the background prediction from the analytic fit...

• Figure 5b

Data from Figure 5 (right).

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The $m_{\text{T}}$ distribution for the low-$R_{\text{T}}$ signal region, comparing the observed data to the background prediction from the analytic fit...

• Figure 6a

Data from Figure 6 (left).

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The $m_{\text{T}}$ distribution for the high-SVJ2 signal region, comparing the observed data to the background prediction from the analytic fit...

• Figure 6b

Data from Figure 6 (right).

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The $m_{\text{T}}$ distribution for the low-SVJ2 signal region, comparing the observed data to the background prediction from the analytic fit...

• Figure 7a

Data from Figure 7 (top left).

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The 95% CL observed upper limits on the product of the cross section and branching fraction from the inclusive search...

• Figure 7a (Median expected exclusion contour 1)

Data from Figure 7 (top left).

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The expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Median expected exclusion contour 2)

Data from Figure 7 (top left).

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The expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Observed exclusion contour 1)

Data from Figure 7 (top left).

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The observed exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Observed exclusion contour 2)

Data from Figure 7 (top left).

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The observed exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Lower 68 expected exclusion contour 1)

Data from Figure 7 (top left).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Lower 68 expected exclusion contour 2)

Data from Figure 7 (top left).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Lower 68 expected exclusion contour 3)

Data from Figure 7 (top left).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Upper 68 expected exclusion contour 1)

Data from Figure 7 (top left).

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The upper 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Upper 68 expected exclusion contour 2)

Data from Figure 7 (top left).

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The upper 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Lower 95 expected exclusion contour 1)

Data from Figure 7 (top left).

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The lower 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Lower 95 expected exclusion contour 2)

Data from Figure 7 (top left).

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The lower 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7a (Upper 95 expected exclusion contour 1)

Data from Figure 7 (top left).

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The upper 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7b

Data from Figure 7 (top right).

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The 95% CL observed upper limits on the product of the cross section and branching fraction from the inclusive search...

• Figure 7b (Median expected exclusion contour 1)

Data from Figure 7 (top right).

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The expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7b (Observed exclusion contour 1)

Data from Figure 7 (top right).

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The observed exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7b (Lower 68 expected exclusion contour 1)

Data from Figure 7 (top right).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7b (Upper 68 expected exclusion contour 1)

Data from Figure 7 (top right).

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The upper 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7b (Lower 95 expected exclusion contour 1)

Data from Figure 7 (top right).

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The lower 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7b (Upper 95 expected exclusion contour 1)

Data from Figure 7 (top right).

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The upper 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7b (Upper 95 expected exclusion contour 2)

Data from Figure 7 (top right).

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The upper 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a

Data from Figure 8 (top left).

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The 95% CL observed upper limits on the product of the cross section and branching fraction from the BDT-based search...

• Figure 8a (Median expected exclusion contour 1)

Data from Figure 8 (top left).

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The expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Median expected exclusion contour 2)

Data from Figure 8 (top left).

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The expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Median expected exclusion contour 3)

Data from Figure 8 (top left).

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The expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Observed exclusion contour 1)

Data from Figure 8 (top left).

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The observed exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Observed exclusion contour 2)

Data from Figure 8 (top left).

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The observed exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Observed exclusion contour 3)

Data from Figure 8 (top left).

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The observed exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Observed exclusion contour 4)

Data from Figure 8 (top left).

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The observed exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Lower 68 expected exclusion contour 1)

Data from Figure 8 (top left).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Lower 68 expected exclusion contour 2)

Data from Figure 8 (top left).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Lower 68 expected exclusion contour 3)

Data from Figure 8 (top left).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Upper 68 expected exclusion contour 1)

Data from Figure 8 (top left).

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The upper 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Upper 68 expected exclusion contour 2)

Data from Figure 8 (top left).

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The upper 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Upper 68 expected exclusion contour 3)

Data from Figure 8 (top left).

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The upper 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Lower 95 expected exclusion contour 1)

Data from Figure 8 (top left).

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The lower 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Lower 95 expected exclusion contour 2)

Data from Figure 8 (top left).

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The lower 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Upper 95 expected exclusion contour 1)

Data from Figure 8 (top left).

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The upper 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Upper 95 expected exclusion contour 2)

Data from Figure 8 (top left).

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The upper 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8a (Upper 95 expected exclusion contour 3)

Data from Figure 8 (top left).

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The upper 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b

Data from Figure 8 (top right).

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The 95% CL observed upper limits on the product of the cross section and branching fraction from the BDT-based search...

• Figure 8b (Median expected exclusion contour 1)

Data from Figure 8 (top right).

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The expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Median expected exclusion contour 2)

Data from Figure 8 (top right).

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The expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Median expected exclusion contour 3)

Data from Figure 8 (top right).

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The expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Observed exclusion contour 1)

Data from Figure 8 (top right).

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The observed exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Observed exclusion contour 2)

Data from Figure 8 (top right).

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The observed exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Lower 68 expected exclusion contour 1)

Data from Figure 8 (top right).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Lower 68 expected exclusion contour 2)

Data from Figure 8 (top right).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Lower 68 expected exclusion contour 3)

Data from Figure 8 (top right).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Lower 68 expected exclusion contour 4)

Data from Figure 8 (top right).

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The lower 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Upper 68 expected exclusion contour 1)

Data from Figure 8 (top right).

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The upper 68% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Lower 95 expected exclusion contour 1)

Data from Figure 8 (top right).

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The lower 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Lower 95 expected exclusion contour 2)

Data from Figure 8 (top right).

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The lower 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Lower 95 expected exclusion contour 3)

Data from Figure 8 (top right).

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The lower 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Lower 95 expected exclusion contour 4)

Data from Figure 8 (top right).

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The lower 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 8b (Upper 95 expected exclusion contour 1)

Data from Figure 8 (top right).

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The upper 95% expected exclusion for the nominal $\text{Z}^{\prime}$ cross section.

• Figure 7c

Data from Figure 7 (bottom).

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The 95% CL upper limits on the product of the cross section and branching fraction from the inclusive search for...

• Figure 8c

Data from Figure 8 (bottom).

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The 95% CL upper limits on the product of the cross section and branching fraction from the BDT-based search for...

• Table 1

Data from Table 1

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The three two-dimensional signal model parameter scans.

• Table 3

Data from Table 3

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• Supplementary Table 6

Data from Table 6

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• Supplementary Table 8

Data from Table 8

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• Supplementary Table 10

Data from Table 10

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Relative efficiencies in % for each step of the event selection process for signals with $m_{\text{Z}^{\prime}} = 4.1\,\text{TeV}$, \$m_{\text{dark}} =...

Version 2 modifications: Minor changes to plot labelling for consistency with the arxiv version of the paper.