CMS-PAS-B2G-24-011

CMS-PAS-B2G-24-011
Search for new resonances decaying into a pair of Higgs bosons in the $ \mathrm{b}\mathrm{b}\tau\tau $ final state in proton-proton collisions at $ \sqrt{s}= $ 13 TeV
CMS Collaboration
2026-07-22

Abstract: A search for resonances decaying into a pair of Standard Model Higgs bosons in the $ b\bar{b}\tau^+\tau^- $ final state is presented. The analysis is based on proton-proton collision data collected by the CMS experiment at the CERN LHC during the 2016-2018 period at a center-of-mass energy of $ \sqrt{s}= $ 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. Narrow spin-0 and spin-2 resonances with masses ranging from 250 to 3000 GeV are considered. Events with at least one hadronically decaying $ \tau $ lepton are selected and a parameterized deep neural network is used to discriminate signals associated with resonances of various masses from the background. This analysis improves upon the most recent searches in this final state by ATLAS and CMS in the mass range 800-1500 GeV. The results are also interpreted in the context of the warped extra dimensions model.
Links: CDS record (PDF) ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Architecture of the parameterized DNN used for the signal extraction. The dedicated \tautau mass regression network is incorporated via \textittransfer learning and connected to the rest of the network from its last layers through a \textitfade-in layer, which slowly introduces the output of the regression to the rest of the network during training.
png pdf	Figure 2: Definition of ABCD method regions used for the evaluation of the QCD background, where the regions are defined using information on the best identified $ \tau_\mathrm{h} $ isolation, and on the sign configuration of the lepton pair: opposite-sign (OS) or same-sign (SS).
png pdf	Figure 3: Pre-fit distributions of the b-jet pair invariant mass for events falling in the res2b category of the $ \tau_\mathrm{e}\tau_\mathrm{h} $ (top-left), $ \tau_\mu\tau_\mathrm{h} $ (top-right) and $ \tau_\mathrm{h}\tau_\mathrm{h} $ (bottom) channels. The shaded bands represent the statistical and systematic uncertainties. The lower panel shows the ratio of data yield over background prediction.
png pdf	Figure 3-a: Pre-fit distributions of the b-jet pair invariant mass for events falling in the res2b category of the $ \tau_\mathrm{e}\tau_\mathrm{h} $ (top-left), $ \tau_\mu\tau_\mathrm{h} $ (top-right) and $ \tau_\mathrm{h}\tau_\mathrm{h} $ (bottom) channels. The shaded bands represent the statistical and systematic uncertainties. The lower panel shows the ratio of data yield over background prediction.
png pdf	Figure 3-b: Pre-fit distributions of the b-jet pair invariant mass for events falling in the res2b category of the $ \tau_\mathrm{e}\tau_\mathrm{h} $ (top-left), $ \tau_\mu\tau_\mathrm{h} $ (top-right) and $ \tau_\mathrm{h}\tau_\mathrm{h} $ (bottom) channels. The shaded bands represent the statistical and systematic uncertainties. The lower panel shows the ratio of data yield over background prediction.
png pdf	Figure 3-c: Pre-fit distributions of the b-jet pair invariant mass for events falling in the res2b category of the $ \tau_\mathrm{e}\tau_\mathrm{h} $ (top-left), $ \tau_\mu\tau_\mathrm{h} $ (top-right) and $ \tau_\mathrm{h}\tau_\mathrm{h} $ (bottom) channels. The shaded bands represent the statistical and systematic uncertainties. The lower panel shows the ratio of data yield over background prediction.
png pdf	Figure 4: Distributions of the parameterized DNN output score used for signal extraction. The plots show all fit channels and categories side by side for each data-taking periods, for the mass point $ m_{\text{X}} = $ 0.28 TeV (top), and $ m_{\text{X}} = $ 1 TeV (bottom). The middle panel depicts the ratio of the data yield over background prediction, while the bottom panel shows the pull of each bin. The signal histograms are scaled to the measured upper limit on the signal cross section.
png pdf	Figure 4-a: Distributions of the parameterized DNN output score used for signal extraction. The plots show all fit channels and categories side by side for each data-taking periods, for the mass point $ m_{\text{X}} = $ 0.28 TeV (top), and $ m_{\text{X}} = $ 1 TeV (bottom). The middle panel depicts the ratio of the data yield over background prediction, while the bottom panel shows the pull of each bin. The signal histograms are scaled to the measured upper limit on the signal cross section.
png pdf	Figure 4-b: Distributions of the parameterized DNN output score used for signal extraction. The plots show all fit channels and categories side by side for each data-taking periods, for the mass point $ m_{\text{X}} = $ 0.28 TeV (top), and $ m_{\text{X}} = $ 1 TeV (bottom). The middle panel depicts the ratio of the data yield over background prediction, while the bottom panel shows the pull of each bin. The signal histograms are scaled to the measured upper limit on the signal cross section.
png pdf	Figure 5: 95% CL limits on the $ \mathrm{p}\mathrm{p} \rightarrow $X$ \rightarrow \mathrm{H}\mathrm{H} $ cross section as a function of $ m_{\text{X}} $, assuming a resonance of spin 0 (left) and of spin 2 (right).
png pdf	Figure 5-a: 95% CL limits on the $ \mathrm{p}\mathrm{p} \rightarrow $X$ \rightarrow \mathrm{H}\mathrm{H} $ cross section as a function of $ m_{\text{X}} $, assuming a resonance of spin 0 (left) and of spin 2 (right).
png pdf	Figure 5-b: 95% CL limits on the $ \mathrm{p}\mathrm{p} \rightarrow $X$ \rightarrow \mathrm{H}\mathrm{H} $ cross section as a function of $ m_{\text{X}} $, assuming a resonance of spin 0 (left) and of spin 2 (right).
png pdf	Figure 6: Observed and expected 95% CL limits on parameters of the spin-0 and spin-2 signal models. (Left) Limits on the ultraviolet cutoff scale $ \Lambda_{\text{R}} $ of the spin-0 radion model, as functions of the radion mass $ m_{\text{R}} $. (Right) Limits on $ \tilde{k} $ of the spin-2 graviton model, as functions of the graviton mass $ m_{\text{G}} $. The shaded bands indicate the direction of exclusion of the parameter space ($ \Lambda_{\text{R}} $ is excluded below the curve, while $ \tilde{k} $ is excluded above the curve).
png pdf	Figure 6-a: Observed and expected 95% CL limits on parameters of the spin-0 and spin-2 signal models. (Left) Limits on the ultraviolet cutoff scale $ \Lambda_{\text{R}} $ of the spin-0 radion model, as functions of the radion mass $ m_{\text{R}} $. (Right) Limits on $ \tilde{k} $ of the spin-2 graviton model, as functions of the graviton mass $ m_{\text{G}} $. The shaded bands indicate the direction of exclusion of the parameter space ($ \Lambda_{\text{R}} $ is excluded below the curve, while $ \tilde{k} $ is excluded above the curve).
png pdf	Figure 6-b: Observed and expected 95% CL limits on parameters of the spin-0 and spin-2 signal models. (Left) Limits on the ultraviolet cutoff scale $ \Lambda_{\text{R}} $ of the spin-0 radion model, as functions of the radion mass $ m_{\text{R}} $. (Right) Limits on $ \tilde{k} $ of the spin-2 graviton model, as functions of the graviton mass $ m_{\text{G}} $. The shaded bands indicate the direction of exclusion of the parameter space ($ \Lambda_{\text{R}} $ is excluded below the curve, while $ \tilde{k} $ is excluded above the curve).

Tables
png pdf	Table 1: Summary of selections applied to the \tautau candidate pair. The lepton $ p_{\mathrm{T}} $ thresholds reported correspond to the minimal cut applied, and tighter requirements may be used depending on the trigger that selected the event.
png pdf	Table 2: Uncertainties (in %) in the QCD background yield estimation. Cells are empty if the QCD estimate is zero.

Summary

A search for resonances decaying into a pair of SM Higgs bosons, in the $ \mathrm{b}\mathrm{b}\tau\tau $ final state has been presented. The analysis is based on proton-proton collision data collected by the CMS experiment at the LHC during 2016--2018 period at a center-of-mass energy of $ \sqrt{s}= $ 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. A parameterized deep neural network is used to discriminate possible signals associated with spin-0 and spin-2 resonances within a mass range from 250 to 3000 GeV from background events. Both spin-0 and spin-2 resonances in the mass range from 250 to 3000 GeV are considered. In the absence of significant excess in data, limits are set on the $ \text{pp}\rightarrow \text{X} \rightarrow \text{HH} $ production cross section for both spin hypotheses, with observed upper limits ranging from 970.7 fb at $ m_{\text{X}}=320 \text{GeV} $ down to 7.4 fb at $ m_{\text{X}}=1250 \text{GeV} $ for spin-0 resonances, and 792.9 fb at $ m_{\text{X}}=320 \text{GeV} $ down to 6.0 fb at $ m_{\text{X}}=1250 \text{GeV} $ for spin-2 resonances. This analysis improves upon the most recent searches in this final state by the ATLAS [21] and CMS [19,18] Collaborations in the mass range 800-1500 GeV, with observed upper limits tighter by up to a factor of five at high masses. The results are also interpreted in the warped extra dimensions model.

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