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| CMS-PAS-EXO-24-033 | ||
| Search for long-lived particles using displaced vertices with low-momentum tracks and missing transverse momentum in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 2025-07-01 | ||
| Abstract: A search for long-lived particles using final states including a displaced vertex with low-momentum tracks, significant missing transverse momentum, and a jet from initial state radiation is presented. The search uses the proton-proton collision data at a center-of-mass energy of 13 TeV collected by the CMS experiment at the CERN LHC in 2017 and 2018 with a total integrated luminosity of 100 fb$ ^{-1} $. This search adopts specific supersymmetric (SUSY) coannihilation scenarios as benchmark signal models, characterized by a next-to-lightest SUSY particle (NLSP) with a mass difference of less than 25 GeV relative to the lightest SUSY particle (LSP). In the top squark coannihilation model, the NLSP is a long-lived top squark, while the LSP is a bino-like neutralino. In the bino-wino coannihilation model, the NLSPs are long-lived wino-like neutralino and prompt wino-like chargino, and the LSP remains a bino-like neutralino. The search excludes top squarks with masses less than 400-1100 GeV and wino-like neutralinos with masses less than 220-550 GeV, depending on the signal parameters. It sets the most stringent limits to date for the top squark coannihilation and bino-wino coannihilation models. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to JHEP. |
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| Figures | |
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Figure 1:
Feynman diagrams for top squark coannihilation model (left) and bino-wino coannihilation model (right). The ISR jet is not shown in the diagrams. |
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Figure 1-a:
Feynman diagrams for top squark coannihilation model (left) and bino-wino coannihilation model (right). The ISR jet is not shown in the diagrams. |
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Figure 1-b:
Feynman diagrams for top squark coannihilation model (left) and bino-wino coannihilation model (right). The ISR jet is not shown in the diagrams. |
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Figure 2:
LLP reconstruction efficiency as a function of the transverse displacement. Bino-wino coannihilation samples with LLP mass of 400 GeV, $ c\tau = $ 20 mm, and $ \Delta m = $ 25 (blue) and 12 (red) GeV are shown in the plot. Tuned (solid) and default (dashed) IVF are compared. |
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Figure 3:
Diagram that shows key features of a displaced vertex. |
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Figure 4:
The vertex $ \alpha_{\text{p}} $ distribution compared between data, simulation, and bino-wino coannihilation sample with LLP mass of 400 GeV, $ c\tau = $ 20 mm, and $ \Delta m = $ 15 GeV. All distributions are normalized to unity. The ratios between data and simulation are shown in the lower panel. |
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Figure 5:
Material map for CMS tracker derived from data. |
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Figure 6:
Definition of signal (orange) and control (blue) regions. Different planes are defined based on the number of good tracks in the vertex. In each plane, different regions are divided according to the $ p_{\mathrm{T}}^\text{miss} $ and $ S_{xy}^{\text{vtx}} $. The letters in the boxes correspond to the region labels described in the text, while the numbers in the boxes correspond to the plane definitions. |
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Figure 7:
The $ \mathrm{K^0_S} $ decay candidate vertex $ L_{xy} $ distribution compared between data and simulation. The ratios between data and simulation are shown in the lower panel. |
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Figure 8:
Observed 95% CL upper limits on the top squark production cross section, as a function of $ m_{\tilde{\mathrm{t}}} $ and $ \Delta m $, for $ \mathcal{B}(\tilde{\mathrm{t}} \to \mathrm{b} \mathrm{f}\mathrm{\overline{f}'} \tilde{\chi}_{1}^{0}) $ of 10% (upper left), 50% (upper right), and 100% (lower). The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plot. |
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Figure 8-a:
Observed 95% CL upper limits on the top squark production cross section, as a function of $ m_{\tilde{\mathrm{t}}} $ and $ \Delta m $, for $ \mathcal{B}(\tilde{\mathrm{t}} \to \mathrm{b} \mathrm{f}\mathrm{\overline{f}'} \tilde{\chi}_{1}^{0}) $ of 10% (upper left), 50% (upper right), and 100% (lower). The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plot. |
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Figure 8-b:
Observed 95% CL upper limits on the top squark production cross section, as a function of $ m_{\tilde{\mathrm{t}}} $ and $ \Delta m $, for $ \mathcal{B}(\tilde{\mathrm{t}} \to \mathrm{b} \mathrm{f}\mathrm{\overline{f}'} \tilde{\chi}_{1}^{0}) $ of 10% (upper left), 50% (upper right), and 100% (lower). The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plot. |
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Figure 8-c:
Observed 95% CL upper limits on the top squark production cross section, as a function of $ m_{\tilde{\mathrm{t}}} $ and $ \Delta m $, for $ \mathcal{B}(\tilde{\mathrm{t}} \to \mathrm{b} \mathrm{f}\mathrm{\overline{f}'} \tilde{\chi}_{1}^{0}) $ of 10% (upper left), 50% (upper right), and 100% (lower). The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plot. |
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Figure 9:
Observed 95% CL upper limits on the production cross section for the bino-wino coannihilation model, as a function of LLP mass and $ c\tau $, for $ \Delta m $ of 12 GeV (upper left), 15 GeV (upper right), 20 GeV (lower left), and 25 GeV (lower right). The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plot. |
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Figure 9-a:
Observed 95% CL upper limits on the production cross section for the bino-wino coannihilation model, as a function of LLP mass and $ c\tau $, for $ \Delta m $ of 12 GeV (upper left), 15 GeV (upper right), 20 GeV (lower left), and 25 GeV (lower right). The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plot. |
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Figure 9-b:
Observed 95% CL upper limits on the production cross section for the bino-wino coannihilation model, as a function of LLP mass and $ c\tau $, for $ \Delta m $ of 12 GeV (upper left), 15 GeV (upper right), 20 GeV (lower left), and 25 GeV (lower right). The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plot. |
png pdf |
Figure 9-c:
Observed 95% CL upper limits on the production cross section for the bino-wino coannihilation model, as a function of LLP mass and $ c\tau $, for $ \Delta m $ of 12 GeV (upper left), 15 GeV (upper right), 20 GeV (lower left), and 25 GeV (lower right). The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plot. |
png pdf |
Figure 9-d:
Observed 95% CL upper limits on the production cross section for the bino-wino coannihilation model, as a function of LLP mass and $ c\tau $, for $ \Delta m $ of 12 GeV (upper left), 15 GeV (upper right), 20 GeV (lower left), and 25 GeV (lower right). The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plot. |
| Tables | |
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Table 1:
Summary of the systematic uncertainties. |
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Table 2:
Event yield of data in the search planes. Predictions for control regions, including all regions in the control plane and Regions B and D in the loose signal plane, are not available because those regions are used to make predictions. In addition, the event yield of the top squark coannihilation sample with $ m_{\tilde{\mathrm{t}}}= $ 1000 GeV, $ \Delta m = $ 20 GeV, and $ \mathcal{B}(\tilde{\mathrm{t}} \to \mathrm{b} \mathrm{f}\mathrm{\overline{f}'} \tilde{\chi}_{1}^{0}) = $ 100% is shown in the row labeled as ``signal''. |
| Summary |
| This note presents a search for long-lived particles in signatures of low-momentum displaced vertices, missing transverse momentum, and an initial state radiation jet. Proton-proton collision data at a center-of-mass energy of 13 TeV collected by the CMS experiment at the CERN LHC, with a total integrated luminosity of 100 fb$ ^{-1} $, are used in the search. Compared with the previous CMS and ATLAS searches using displaced vertices, this search targets vertices with significantly lower momentum. This search adopts specific supersymmetric (SUSY) coannihilation scenarios as benchmark signal models, characterized by a long-lived next-to-lightest SUSY particle (NLSP) with a mass difference of less than 25 GeV relative to the lightest SUSY particle (LSP). In the top squark coannihilation model, the NLSP is a top squark, while the LSP is a bino-like neutralino. In the bino-wino coannihilation model, the NLSPs are long-lived wino-like neutralino and prompt wino-like chargino, and the LSP remains a bino-like neutralino. This search reconstructs displaced vertices using a customized reconstruction algorithm based on the adaptive vertex fitter [60]. In addition, the background estimation method using transfer factors allows targeting multiple search regions, thus enhancing the search sensitivity. The search shows good overall agreement between the background predictions and observed event yields across most search regions. The resulting $ p $-value is 0.5, indicating no significant deviation from the background expectation. It excludes top squark masses less than 400-1100 GeV and wino-like neutralinos with masses less than 220 -550 GeV, depending on signal parameters. This search is the first LHC search that targets displaced vertices and shows sensitivity for hadronically decaying long-lived particles with a mass difference of less than 25 GeV. It sets the most stringent upper limits to date for the top squark coannihilation and bino-wino coannihilation signal models. |
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