CMS-PAS-EXO-23-003

CMS-PAS-EXO-23-003
Search for soft unclustered energy patterns in association with a Z 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 Z 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 with two light leptons compatible with a Z boson decay and a high multiplicity of low-momentum tracks are explored for the first time. The results show no significant excess over the standard model expectation and are used to set upper limits on the cross section of the associated SUEP+Z production process. Model-agnostic results are provided for reinterpretation with other signal models.
Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: A schematic Feynman diagram of the production of a SUEP shower in association with a leptonically decaying Z boson. The shaded triangle represents the dark shower that produces the SUEP final state.
png pdf	Figure 2: Distributions of $n_{\text{constituent}}^{\text{SUEP}}$ in the extended ABCD regions in CRDY (upper) and CRTT (lower), showing the observed data, the predictions from both the CR and CR+PR fits, and several prefit signal samples. The SER, region A, corresponds to the eight rightmost bins of the plot. Solid vertical lines separate regions with different $p_{\mathrm{T}}^{\text{j}_{1}}$ values. Dotted vertical lines separate the different extended ABCD regions. The shaded vertical (horizontal) bands correspond to the overall uncertainty in the background estimation in the CR fit (CR+PR fit). In the lower panel, the shaded bands correspond to the statistical uncertainty in the data. In the PR (lower), the data are weighted by the ratio of delivered over collected luminosity.
png pdf	Figure 2-a: Distributions of $n_{\text{constituent}}^{\text{SUEP}}$ in the extended ABCD regions in CRDY (upper) and CRTT (lower), showing the observed data, the predictions from both the CR and CR+PR fits, and several prefit signal samples. The SER, region A, corresponds to the eight rightmost bins of the plot. Solid vertical lines separate regions with different $p_{\mathrm{T}}^{\text{j}_{1}}$ values. Dotted vertical lines separate the different extended ABCD regions. The shaded vertical (horizontal) bands correspond to the overall uncertainty in the background estimation in the CR fit (CR+PR fit). In the lower panel, the shaded bands correspond to the statistical uncertainty in the data. In the PR (lower), the data are weighted by the ratio of delivered over collected luminosity.
png pdf	Figure 2-b: Distributions of $n_{\text{constituent}}^{\text{SUEP}}$ in the extended ABCD regions in CRDY (upper) and CRTT (lower), showing the observed data, the predictions from both the CR and CR+PR fits, and several prefit signal samples. The SER, region A, corresponds to the eight rightmost bins of the plot. Solid vertical lines separate regions with different $p_{\mathrm{T}}^{\text{j}_{1}}$ values. Dotted vertical lines separate the different extended ABCD regions. The shaded vertical (horizontal) bands correspond to the overall uncertainty in the background estimation in the CR fit (CR+PR fit). In the lower panel, the shaded bands correspond to the statistical uncertainty in the data. In the PR (lower), the data are weighted by the ratio of delivered over collected luminosity.
png pdf	Figure 3: Distributions of $n_{\text{constituent}}^{\text{SUEP}}$ in the extended ABCD regions in the PR, showing the observed data, the predictions from both the CR and CR+PR fits, and several prefit signal samples. The SER, region A, corresponds to the eight rightmost bins of the plot. Solid vertical lines separate regions with different $p_{\mathrm{T}}^{\text{j}_{1}}$ values. Dotted vertical lines separate the different extended ABCD regions. The shaded vertical (horizontal) bands correspond to the overall uncertainty in the background estimation in the CR fit (CR+PR fit). In the lower panel, the shaded bands correspond to the statistical uncertainty in the data. In the PR (lower), the data are weighted by the ratio of delivered over collected luminosity.
png pdf	Figure 4: Distributions of $n_{\text{constituent}}^{\text{SUEP}}$ in the extended ABCD regions in the SR, showing the observed data, the predictions from both the CR and CR+SR fits, and several prefit signal models. The signal-enriched region A corresponds to the eight rightmost bins of the plot. Solid vertical lines separate regions with different $p_{\mathrm{T}}^{\text{j}_{1}}$ values. Dotted vertical lines separate the different regions of the extended ABCD. The shaded vertical (horizontal) bands correspond to the overall uncertainty on the background estimation in the CR fit (CR+SR fit). In the lower panel, the shaded bands correspond to the statistical uncertainty in the data.
png pdf	Figure 5: Upper: 95% CL upper limits on the product of the Higgs boson to SUEP branching fraction for several different signal models with fully hadronic A' decays and $m_{\phi}=$ 2 or 4 GeV. The horizontal dotted line represents the predicted signal cross section for a Higgs boson mediator with 100% branching fraction to SUEP and SM Z boson decays to leptons. Lower: interpretation of the results for a Higgs boson mediator and fully hadronic SUEP decays. The background color map represents the observed upper limit for each signal model; the contour at which the observed (median expected) upper limit on the branching fraction equals unity is shown as a solid (dotted) black line.
png pdf	Figure 5-a: Upper: 95% CL upper limits on the product of the Higgs boson to SUEP branching fraction for several different signal models with fully hadronic A' decays and $m_{\phi}=$ 2 or 4 GeV. The horizontal dotted line represents the predicted signal cross section for a Higgs boson mediator with 100% branching fraction to SUEP and SM Z boson decays to leptons. Lower: interpretation of the results for a Higgs boson mediator and fully hadronic SUEP decays. The background color map represents the observed upper limit for each signal model; the contour at which the observed (median expected) upper limit on the branching fraction equals unity is shown as a solid (dotted) black line.
png pdf	Figure 5-b: Upper: 95% CL upper limits on the product of the Higgs boson to SUEP branching fraction for several different signal models with fully hadronic A' decays and $m_{\phi}=$ 2 or 4 GeV. The horizontal dotted line represents the predicted signal cross section for a Higgs boson mediator with 100% branching fraction to SUEP and SM Z boson decays to leptons. Lower: interpretation of the results for a Higgs boson mediator and fully hadronic SUEP decays. The background color map represents the observed upper limit for each signal model; the contour at which the observed (median expected) upper limit on the branching fraction equals unity is shown as a solid (dotted) black line.
png pdf	Figure 6: Upper: 95% CL upper limits on the product of the Higgs boson to SUEP branching fraction for several different signal models with dominantly leptonic A' decays and $m_{\phi}=$ 2 or 4 GeV. The horizontal dotted line represents the predicted signal cross section for a Higgs boson mediator with 100% branching fraction to SUEP and SM Z boson decays to leptons. Lower: interpretation of the results for a Higgs boson mediator and fully hadronic SUEP decays. The background color map represents the observed upper limit for each signal model; the contour at which the observed (median expected) upper limit on the branching fraction equals unity is shown as a solid (dotted) black line.
png pdf	Figure 6-a: Upper: 95% CL upper limits on the product of the Higgs boson to SUEP branching fraction for several different signal models with dominantly leptonic A' decays and $m_{\phi}=$ 2 or 4 GeV. The horizontal dotted line represents the predicted signal cross section for a Higgs boson mediator with 100% branching fraction to SUEP and SM Z boson decays to leptons. Lower: interpretation of the results for a Higgs boson mediator and fully hadronic SUEP decays. The background color map represents the observed upper limit for each signal model; the contour at which the observed (median expected) upper limit on the branching fraction equals unity is shown as a solid (dotted) black line.
png pdf	Figure 6-b: Upper: 95% CL upper limits on the product of the Higgs boson to SUEP branching fraction for several different signal models with dominantly leptonic A' decays and $m_{\phi}=$ 2 or 4 GeV. The horizontal dotted line represents the predicted signal cross section for a Higgs boson mediator with 100% branching fraction to SUEP and SM Z boson decays to leptons. Lower: interpretation of the results for a Higgs boson mediator and fully hadronic SUEP decays. The background color map represents the observed upper limit for each signal model; the contour at which the observed (median expected) upper limit on the branching fraction equals unity is shown as a solid (dotted) black line.
png pdf	Figure 7: Upper: 95% CL upper limits on the product of the Higgs boson to SUEP branching fraction for several different signal models with dominantly hadronic A' decays and $m_{\phi}=$ 2 or 4 GeV. The horizontal dotted line represents the predicted signal cross section for a Higgs boson mediator with 100% branching fraction to SUEP and SM Z boson decays to leptons. Lower: interpretation of the results for a Higgs boson mediator and fully hadronic SUEP decays. The background color map represents the observed upper limit for each signal model; the contour at which the observed (median expected) upper limit on the branching fraction equals unity is shown as a solid (dotted) black line.
png pdf	Figure 7-a: Upper: 95% CL upper limits on the product of the Higgs boson to SUEP branching fraction for several different signal models with dominantly hadronic A' decays and $m_{\phi}=$ 2 or 4 GeV. The horizontal dotted line represents the predicted signal cross section for a Higgs boson mediator with 100% branching fraction to SUEP and SM Z boson decays to leptons. Lower: interpretation of the results for a Higgs boson mediator and fully hadronic SUEP decays. The background color map represents the observed upper limit for each signal model; the contour at which the observed (median expected) upper limit on the branching fraction equals unity is shown as a solid (dotted) black line.
png pdf	Figure 7-b: Upper: 95% CL upper limits on the product of the Higgs boson to SUEP branching fraction for several different signal models with dominantly hadronic A' decays and $m_{\phi}=$ 2 or 4 GeV. The horizontal dotted line represents the predicted signal cross section for a Higgs boson mediator with 100% branching fraction to SUEP and SM Z boson decays to leptons. Lower: interpretation of the results for a Higgs boson mediator and fully hadronic SUEP decays. The background color map represents the observed upper limit for each signal model; the contour at which the observed (median expected) upper limit on the branching fraction equals unity is shown as a solid (dotted) black line.
png pdf	Figure 8: 95% CL upper limits on the signal yield from the model-agnostic fit, assuming no signal contamination in CRTT and CRDY, for different minimum $n_{\text{constituent}}^{\text{SUEP}}$ values.

Tables
png pdf	Table 1: The requirements for the SR, the two CRs, and the PR, and their usage in this search. The symbol $p_{\mathrm{T}}\{X\}$ denotes the transverse momentum of the reconstructed object $X$ ; $N_{\mathrm{b}\,\text{tag}}$ denotes the number of b tagged jets; $\ell_1$ and $\ell_2$ denote the leading and subleading lepton in each event; and $m_{\ell\ell}$ denotes the invariant mass of the dilepton system.
png pdf	Table 2: Summary of systematic uncertainties considered in this search, specifying for each: the process it effects; whether it is treated as a correlated uncertainty in the $n_{\text{constituent}}^{\text{SUEP}}$ distribution, an uncorrelated uncertainty per $n_{\text{constituent}}^{\text{SUEP}}$ bin, or a correlated uncertainty in the overall normalization; and its overall effect size. The overall effect is quantified as the minimum and maximum variation in the predicted yields of the associated process across all $n_{\text{constituent}}^{\text{SUEP}}$ bins. The effect of the limited number of simulated signal events varies per model, depending strongly on the $n_{\text{constituent}}^{\text{SUEP}}$ distribution. At the Higgs boson production cross section, the amount of signal events corresponds to an effective luminosity of 8000 fb $^{-1}$ .

Summary

This note presents the first search for final states with a large-radius jet composed of low-momentum, isotropically distributed particles---a soft unclustered energy pattern or SUEP---and a Z boson. Events are selected at trigger level based on the presence of leptons arising from the leptonic decays of the Z boson. This strategy improves the sensitivity of the search to Higgs boson mediators by four (two) orders of magnitude in the signal cross section (branching fraction) compared to previous results [14]. No significant deviation from the standard model expectation is observed, and the most stringent limits to date are obtained for SUEP production in association with a vector boson. SUEP models with a Higgs boson mediator are excluded for low temperatures (

$T_{\text{D}} <$ 3 GeV) and low dark meson masses (

$m_{\phi} <$ 7 GeV). Additional model-agnostic limits on the signal yield are provided for the purpose of reinterpretation.

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