CMS-PAS-B2G-24-014

CMS-PAS-B2G-24-014
Search for heavy resonances decaying into two Higgs bosons in the $ \mathrm{b}\bar{\mathrm{b}} \tau^{+}\tau^{-} $ final state in proton-proton collisions at $ \sqrt{s} = $ 13 TeV
CMS Collaboration
2025-08-27

Abstract: A search is presented for massive narrow-width resonances in the mass range of 1 $ \text{-} $ 4.5 TeV decaying into pairs of Higgs bosons (HH), using proton-proton collision data at a center-of-mass energy of 13 TeV collected with the CMS detector at the LHC during the 2016 $ \text{-} $ 2018 data-taking. The data correspond to an integrated luminosity of 138 fb$ ^{-1} $. The analysis targets final states where one Higgs boson decays into a pair of bottom quarks and the other into a pair of tau leptons, $ \mathrm{X}\rightarrow\mathrm{HH}\rightarrow \mathrm{b}\bar{\mathrm{b}} \tau^{+}\tau^{-} $. The observed data are found to be consistent with standard model background expectations. Upper limits at 95% confidence level are set on the production cross section for resonant HH production for masses between 1 and 4.5 TeV. This analysis sets the most sensitive LHC limits to date on $ \mathrm{X}\rightarrow\mathrm{HH}\rightarrow \mathrm{b}\bar{\mathrm{b}} \tau^{+}\tau^{-} $ decays in the mass range of 1.4 to 4.5 TeV.
Links: CDS record (PDF) ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Representative Feynman diagram for the production of either a spin-0 radion or a spin-2 graviton X, which decays into two SM Higgs bosons. The Higgs boson pairs decay into a $ \mathrm{b}\overline{\mathrm{b}} \tau^+\tau^- $ final state.
png pdf	Figure 2: Invariant mass of the di-tau system reconstructed by FASTMTT after the full event selection. $ \tau_h\tau_h $ channel is shown on the left and $ \ell\tau_h $ channel on the right. The data are compared with simulation, and the grey uncertainty bands represent postfit uncertainties of a few prominent parameters in the fit along with statistical uncertainties.
png pdf	Figure 2-a: Invariant mass of the di-tau system reconstructed by FASTMTT after the full event selection. $ \tau_h\tau_h $ channel is shown on the left and $ \ell\tau_h $ channel on the right. The data are compared with simulation, and the grey uncertainty bands represent postfit uncertainties of a few prominent parameters in the fit along with statistical uncertainties.
png pdf	Figure 2-b: Invariant mass of the di-tau system reconstructed by FASTMTT after the full event selection. $ \tau_h\tau_h $ channel is shown on the left and $ \ell\tau_h $ channel on the right. The data are compared with simulation, and the grey uncertainty bands represent postfit uncertainties of a few prominent parameters in the fit along with statistical uncertainties.
png pdf	Figure 3: Invariant mass ($ \mathrm{M}_\mathrm{H(bb)} $) of the leading AK8 jet (obtained from ParticleNet regression) in the event after the full event selection. The signal region (SR) is defined as 100 GeV $ \leq \mathrm{M} _ \mathrm{H(bb)} \leq $ 150 GeV. Sideband (SB) regions are defined on either side of the SR. $ \tau_h\tau_h $ channel is shown on the left and $ \ell\tau_h $ channel on the right. The data are compared with simulation, and the grey uncertainty bands in the plot represent postfit uncertainties of a few prominent parameters in the fit along with statistical uncertainties.
png pdf	Figure 3-a: Invariant mass ($ \mathrm{M}_\mathrm{H(bb)} $) of the leading AK8 jet (obtained from ParticleNet regression) in the event after the full event selection. The signal region (SR) is defined as 100 GeV $ \leq \mathrm{M} _ \mathrm{H(bb)} \leq $ 150 GeV. Sideband (SB) regions are defined on either side of the SR. $ \tau_h\tau_h $ channel is shown on the left and $ \ell\tau_h $ channel on the right. The data are compared with simulation, and the grey uncertainty bands in the plot represent postfit uncertainties of a few prominent parameters in the fit along with statistical uncertainties.
png pdf	Figure 3-b: Invariant mass ($ \mathrm{M}_\mathrm{H(bb)} $) of the leading AK8 jet (obtained from ParticleNet regression) in the event after the full event selection. The signal region (SR) is defined as 100 GeV $ \leq \mathrm{M} _ \mathrm{H(bb)} \leq $ 150 GeV. Sideband (SB) regions are defined on either side of the SR. $ \tau_h\tau_h $ channel is shown on the left and $ \ell\tau_h $ channel on the right. The data are compared with simulation, and the grey uncertainty bands in the plot represent postfit uncertainties of a few prominent parameters in the fit along with statistical uncertainties.
png pdf	Figure 4: Post-fit reconstructed mass distribution of resonance X ($ \text{M}_\text{X} $) in the SR (left) and SB (right) after applying the complete selection criteria. The plots correspond to the merged $ \tau_h\tau_h $ and $ \ell\tau_h $ channels. Minor background contributions are grouped into a single category labeled as others.
png pdf	Figure 4-a: Post-fit reconstructed mass distribution of resonance X ($ \text{M}_\text{X} $) in the SR (left) and SB (right) after applying the complete selection criteria. The plots correspond to the merged $ \tau_h\tau_h $ and $ \ell\tau_h $ channels. Minor background contributions are grouped into a single category labeled as others.
png pdf	Figure 4-b: Post-fit reconstructed mass distribution of resonance X ($ \text{M}_\text{X} $) in the SR (left) and SB (right) after applying the complete selection criteria. The plots correspond to the merged $ \tau_h\tau_h $ and $ \ell\tau_h $ channels. Minor background contributions are grouped into a single category labeled as others.
png pdf	Figure 5: Expected and observed upper limits at 95% CL on the production cross section of resonant HH production for a spin-0 (left) and spin-2 (right) narrow resonance hypothesis.
png pdf	Figure 5-a: Expected and observed upper limits at 95% CL on the production cross section of resonant HH production for a spin-0 (left) and spin-2 (right) narrow resonance hypothesis.
png pdf	Figure 5-b: Expected and observed upper limits at 95% CL on the production cross section of resonant HH production for a spin-0 (left) and spin-2 (right) narrow resonance hypothesis.

Summary

A search is presented for heavy resonant Higgs boson pair (HH) production in the $ \mathrm{b}\overline{\mathrm{b}}\tau^+\tau^- $ final state, exploring resonance masses between 1 and 4.5 TeV. The analysis is based on proton-proton collision data collected with the CMS detector during LHC Run 2 (2016--2018), corresponding to an integrated luminosity of 138 fb$ ^{-1} $ at a center-of-mass energy of 13 TeV. In this mass regime, the Higgs bosons produced are boosted, resulting in collimated decay products. The reconstruction and identification of such boosted objects are enhanced using advanced machine learning techniques, including a graph neural network for merged $ \mathrm{b}\overline{\mathrm{b}} $ jets and a convolutional neural network for boosted $ \tau^+\tau^- $ identification. No significant deviation from the standard model background expectation is observed and 95% confidence level upper limits are set on the production cross section of a heavy resonance decaying to HH, evaluated independently for both spin-0 and spin-2 hypotheses. With respect to previous CMS and ATLAS results, this analysis, using the full Run 2 dataset sets the most sensitive upper bounds to date on the production of $ \mathrm{X} $ \rightarrow $ \mathrm{HH} \rightarrow \mathrm{b}\overline{\mathrm{b}} \tau^+\tau^- $ at the LHC in the mass range of 1.4 to 4.5 TeV.

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