CMS-PAS-EXO-24-030

CMS-PAS-EXO-24-030
Search for soft unclustered energy patterns in association with a W boson in proton-proton collisions at 13 TeV
CMS Collaboration
27 March 2025

Abstract: A search for soft unclustered energy patterns (SUEPs) produced in association with a W boson is presented. The analysis is based on proton-proton collision data corresponding to an integrated luminosity of 138 fb $^{-1}$ , collected between 2016 and 2018 with the CMS detector at $\sqrt{s}=$ 13 TeV. Final states containing a W boson candidate and a high multiplicity of soft tracks are explored for the first time. Upper limits are set on the branching fraction for the Higgs boson decay to a SUEP.
Links: CDS record (PDF) ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 3: The observed and fitted distributions of the number of constituents in the SUEP candidate in all regions of the SR, and the distributions from several representative signal hypotheses.
png pdf	Figure 4: The 95% CL exclusion limits on the branching fraction for the Higgs boson decay to a SUEP for several different signal models are shown as a function of $\log_{2} (T_{\text{D}}/m_{\phi})$ . Upper: two representative $m_{\phi}$ values, 2 and 4 GeV, with fully hadronic A' decays ( $\mathrm{A}' \to \pi^{+}\pi^{-}$ with $\mathcal{B} = 100%$ ) are shown. Lower: comparison of the limits for the three different final-state flavor compositions considered in this search, which correspond to the different values of $m_{\mathrm{A}'}$ , for $m_{\phi} =$ 2 GeV. The horizontal dash-dotted lines represent a Higgs boson mediator with 100% branching fraction to a SUEP; above each line, the region with a branching fraction greater than unity is shaded to indicate it as physically forbidden.
png pdf	Figure 4-a: The 95% CL exclusion limits on the branching fraction for the Higgs boson decay to a SUEP for several different signal models are shown as a function of $\log_{2} (T_{\text{D}}/m_{\phi})$ . Upper: two representative $m_{\phi}$ values, 2 and 4 GeV, with fully hadronic A' decays ( $\mathrm{A}' \to \pi^{+}\pi^{-}$ with $\mathcal{B} = 100%$ ) are shown. Lower: comparison of the limits for the three different final-state flavor compositions considered in this search, which correspond to the different values of $m_{\mathrm{A}'}$ , for $m_{\phi} =$ 2 GeV. The horizontal dash-dotted lines represent a Higgs boson mediator with 100% branching fraction to a SUEP; above each line, the region with a branching fraction greater than unity is shaded to indicate it as physically forbidden.
png pdf	Figure 4-b: The 95% CL exclusion limits on the branching fraction for the Higgs boson decay to a SUEP for several different signal models are shown as a function of $\log_{2} (T_{\text{D}}/m_{\phi})$ . Upper: two representative $m_{\phi}$ values, 2 and 4 GeV, with fully hadronic A' decays ( $\mathrm{A}' \to \pi^{+}\pi^{-}$ with $\mathcal{B} = 100%$ ) are shown. Lower: comparison of the limits for the three different final-state flavor compositions considered in this search, which correspond to the different values of $m_{\mathrm{A}'}$ , for $m_{\phi} =$ 2 GeV. The horizontal dash-dotted lines represent a Higgs boson mediator with 100% branching fraction to a SUEP; above each line, the region with a branching fraction greater than unity is shaded to indicate it as physically forbidden.
png pdf	Figure 5: The 95% CL exclusion limits on the branching ratio for the Higgs boson decay to a SUEP are shown as a function of $m_{\phi}$ and $\log_{2} (T_{\text{D}}/m_{\phi})$ , with $m_{\mathrm{A}'}=$ 1.0 GeV ( $\mathrm{A}' \to \pi^{+}\pi^{-}$ with $\mathcal{B}=100%$ ). The values between explicitly simulated signal models are determined via logarithmic interpolation. The contour at which the observed (median expected) upper limit on the branching fraction equals unity is shown as a solid (dotted) black line.

Tables
png pdf	Table 1: For each bin in the SER, the prediction-observation agreement in the CR is shown, along with the nominal statistical uncertainty in the CR prediction, the final uncertainty accounting for the slightly larger disagreement in the fourth bin, the statistical uncertainty in the SR, and the final value of the uncertainty in the $n_{\text{constituent}}^{\text{SUEP}}$ distribution.

Summary

In summary, this note presents the first search for soft unclustered energy patterns (SUEPs) produced in association with a W boson. Data corresponding to an integrated luminosity of 138 fb

$^{-1}$ are used, collected with triggers requiring a single muon or electron and reconstructed with the full offline processing. This strategy preferentially selects events with a W boson recoiling against a SUEP candidate cluster of many low-momentum, isotropically-distributed charged particles. The number of tracks and the associated sphericity of the SUEP candidate are used to discriminate between the signal and the background from standard model processes, whose contributions are estimated from data. Limits are placed on the most SUEP-like hidden valley scenarios with highly isotropic dark showers arising from a 125 GeV Higgs boson and producing a large multiplicity of tracks.

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