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CMS-PAS-B2G-21-003
Search for a massive scalar resonance decaying to a light scalar and a Higgs boson in the four b quark final state with boosted topology
Abstract: We search for the resonant production of a new massive scalar X decaying into a new light scalar Y and the standard model Higgs boson H through the process $\mathrm{X}\,\,\to\,\,\mathrm{Y}\mathrm{H}\,\,\to\,\,\mathrm{b}\overline{\mathrm{b}}\mathrm{b}\overline{\mathrm{b}}$. The search uses proton-proton collision data from the CERN LHC, collected at a centre-of-mass energy of 13 TeV in 2016-2018 and corresponding to an integrated luminosity of 138 fb$^{-1}$. The search is dedicated to mass ranges of X (0.9-4 TeV) and Y (60-600 GeV) where both the Y and the H are highly Lorentz-boosted and therefore their b quark-antiquark daughter particles are sufficiently collimated to be reconstructed using single large-area jets each. The mass of the one of the jets is required to be compatible with that of the Higgs boson, which is 125 GeV. A scan is performed in a two dimensional phase space spanned by the mass of the other jet, associated with Y, and the invariant mass of the two jets used to reconstruct X. The results are interpreted in the context of scalar resonances predicted in the next-to-minimal supersymmetric standard model and upper limits are placed on the production cross section as a function of the masses of X and Y. This is the first search for this process using Lorentz-boosted event topologies and it significantly extends the constraints on the model under consideration.
Figures & Tables Summary Additional Figures References CMS Publications
Figures

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Figure 1:
The distributions of the H and the Y candidate jets' ParticleNet scores for the signal with ${M_{\mathrm{X}}} =$ 1600 GeV and ${M_{\mathrm{Y}}} =$ 90 GeV (filled squares) and multijets background (open circles). The grid lines show the different event categories defined using the ParticleNet scores of the two jets. A description of the regions is given in Table 1 and in the text.

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Figure 2:
The $ {M_{\rm J}^{\mathrm{Y}}}$ (left) and ${M_{\rm JJ}}$ (right) distributions for the number of observed events (black markers) compared with the estimated backgrounds (filled histograms) in the signal region 1. The distributions expected from the signal under three ${M_{\mathrm{X}}}$ and ${M_{\mathrm{Y}}}$ hypotheses and assuming a cross section of 1 fb are also shown. The lower panels show the "Pulls'' defined as (observed events$-$expected events)$/\sqrt {\sigma _{obs}^{2} + \sigma _{exp}^{2}}$, where $\sigma _{obs}$ and $\sigma _{exp}$ are the statistical and total uncertainties in the observation and the background estimation, respectively.

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Figure 2-a:
The $ {M_{\rm J}^{\mathrm{Y}}}$ distribution for the number of observed events (black markers) compared with the estimated backgrounds (filled histograms) in the signal region 1. The distributions expected from the signal under three ${M_{\mathrm{X}}}$ and ${M_{\mathrm{Y}}}$ hypotheses and assuming a cross section of 1 fb are also shown. The lower panel shows the "Pulls'' defined as (observed events$-$expected events)$/\sqrt {\sigma _{obs}^{2} + \sigma _{exp}^{2}}$, where $\sigma _{obs}$ and $\sigma _{exp}$ are the statistical and total uncertainties in the observation and the background estimation, respectively.

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Figure 2-b:
The ${M_{\rm JJ}}$ distribution for the number of observed events (black markers) compared with the estimated backgrounds (filled histograms) in the signal region 1. The distributions expected from the signal under three ${M_{\mathrm{X}}}$ and ${M_{\mathrm{Y}}}$ hypotheses and assuming a cross section of 1 fb are also shown. The lower panel shows the "Pulls'' defined as (observed events$-$expected events)$/\sqrt {\sigma _{obs}^{2} + \sigma _{exp}^{2}}$, where $\sigma _{obs}$ and $\sigma _{exp}$ are the statistical and total uncertainties in the observation and the background estimation, respectively.

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Figure 3:
The 95% confidence level expected (left) and observed (right) upper limits on $\sigma ({\mathrm{p}} {\mathrm{p}} \,\to \, {\mathrm{X} \,\to \,\mathrm{Y} \mathrm{H} \,\to \,\mathrm{b} \mathrm{\bar{b}} \mathrm{b} \mathrm{\bar{b}}})$ for different values of ${M_{\mathrm{X}}}$ and ${M_{\mathrm{Y}}}$.

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Figure 3-a:
The 95% confidence level expected upper limits on $\sigma ({\mathrm{p}} {\mathrm{p}} \,\to \, {\mathrm{X} \,\to \,\mathrm{Y} \mathrm{H} \,\to \,\mathrm{b} \mathrm{\bar{b}} \mathrm{b} \mathrm{\bar{b}}})$ for different values of ${M_{\mathrm{X}}}$ and ${M_{\mathrm{Y}}}$.

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Figure 3-b:
The 95% confidence level observed upper limits on $\sigma ({\mathrm{p}} {\mathrm{p}} \,\to \, {\mathrm{X} \,\to \,\mathrm{Y} \mathrm{H} \,\to \,\mathrm{b} \mathrm{\bar{b}} \mathrm{b} \mathrm{\bar{b}}})$ for different values of ${M_{\mathrm{X}}}$ and ${M_{\mathrm{Y}}}$.
Tables

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Table 1:
Definition of the signal, sideband, and validation regions used for background estimation. The regions are defined in terms of the ParticleNet discriminators of the H and Y candidate jets, as shown in Fig. 1.
Summary
A search for massive scalar resonances X and Y, where X decays to the lighter Y and the standard model Higgs boson H, is conducted in LHC proton-proton collision data collected by the CMS detector between 2016 and 2018 and corresponding to an integrated luminosity of 138 fb$^{-1}$. The considered decay modes of both Y and H are to a b quark-antiquark pairs each. Events are selected assuming very high Lorentz-boost of both the Y and the H, for which specialized jet substructure and identification techniques are used. The background, composed of multijets and $\mathrm{t\bar{t}}$, is estimated using data control samples and Monte Carlo simulations. A binned likelihood fit to the data is performed using the reconstructed mass distributions of the X and Y candidates. Upper limits are set on the cross section of the process $\mathrm{X} \,\,\to\,\, \mathrm{Y} \mathrm{H} \,\,\to\,\, \mathrm{b\bar{b}}\mathrm{b\bar{b}}$ for assumed masses of X in the range 0.9-4 TeV and Y between 60-600 GeV. The results are interpreted in the context of the next-to-minimal supersymmetric standard model (NMSSM) scalar sector. This search significantly extends limit ranges of NMSSM scalars over previous analyses and places the most stringent cross section limits over much of the explored X and Y mass ranges to date.
Additional Figures

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Additional Figure 1:
The ParticleNet score of the leading $p_{\mathrm{T}}$ AK8 jet in 2016 simulations. The filled histograms show the various standard model background processes and the lines show the signal for three different mass hypotheses of the X and Y resonances. The main backgrounds are the standard model multijet and ${{\mathrm {t}\overline {\mathrm {t}}}} $+jets processes. The minor backgrounds are the V+jets (V= W and Z) and single top production, which are not estimated separately from the multijets background.

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Additional Figure 2:
The ParticleNet score of the leading $p_{\mathrm{T}}$ AK8 jet in 2017 simulations. The filled histograms show the main backgrounds, the standard model multijet and ${{\mathrm {t}\overline {\mathrm {t}}}} $+jets processes. The lines show the signal for three different mass hypotheses of the X and Y resonances.

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Additional Figure 3:
The ParticleNet score of the leading $p_{\mathrm{T}}$ AK8 jet in 2018 simulations. The filled histograms show the main backgrounds, the standard model multijet and ${{\mathrm {t}\overline {\mathrm {t}}}} $+jets processes. The lines show the signal for three different mass hypotheses of the X and Y resonances.

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Additional Figure 4:
The ParticleNet score of the second-leading $p_{\mathrm{T}}$ AK8 jet in 2016 simulations. The filled histograms show the various standard model background processes and the lines show the signal for three different mass hypotheses of the X and Y resonances. The main backgrounds are the standard model multijet and ${{\mathrm {t}\overline {\mathrm {t}}}} $+jets processes. The minor backgrounds are the V+jets (V= W and Z) and single top production, which are not estimated separately from the multijets background.

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Additional Figure 5:
The ParticleNet score of the second-leading $p_{\mathrm{T}}$ AK8 jet in 2017 simulations. The filled histograms show the main backgrounds, the standard model multijet and ${{\mathrm {t}\overline {\mathrm {t}}}} $+jets processes. The lines show the signal for three different mass hypotheses of the X and Y resonances.

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Additional Figure 6:
The ParticleNet score of the second-leading $p_{\mathrm{T}}$ AK8 jet in 2018 simulations. The filled histograms show the main backgrounds, the standard model multijet and ${{\mathrm {t}\overline {\mathrm {t}}}} $+jets processes. The lines show the signal for three different mass hypotheses of the X and Y resonances.

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Additional Figure 7:
The ParticleNet ROC curves in 2017 simulations for $M_{\mathrm{X}}$=1600 GeV and different mass hypotheses of the Y resonance. The horizontal dashed lines show the mistag rates for tight and loose working points.

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Additional Figure 8:
Initial $R_{P/F}$ measured for the VS3 and VB2 region in the full RunII data and used in the validation fit. Simulation prediction of the $\mathrm{t\bar{t}}$ distribution is subtracted from the combined observe data and a second order polynomial is fitted to the result.

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Additional Figure 9:
Initial $R_{P/F}$ measured for the VS4 and VB2 region in the full RunII data and used in the validation fit. Simulation prediction of the $\mathrm{t\bar{t}}$ distribution is subtracted from the combined observe data and a second order polynomial is fitted to the result.

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Additional Figure 10:
The $R_{\text{Ratio}}$ for the VS1 after the validation fit.

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Additional Figure 11:
The $R_{\text{Ratio}}$ for the VS2 after the validation fit.

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Additional Figure 12:
The final transfer function, $R_{P/F}^{\text{init}}\times R_{\text{Ratio}}$, in the VS1 after the validation fit.

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Additional Figure 13:
The final transfer function, $R_{P/F}^{\text{init}}\times R_{\text{Ratio}}$, in the VS2 after the validation fit.

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Additional Figure 14:
The $M_{\mathrm{JY}}$ distribution for the number of observed events (black markers) compared with the estimated backgrounds (filled histograms) in the validation signal-like region 1.

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Additional Figure 15:
The $M_{\mathrm{JJ}}$ distribution for the number of observed events (black markers) compared with the estimated backgrounds (filled histograms) in the validation signal-like region 1.

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Additional Figure 16:
The $M_{\mathrm{JY}}$ distribution for the number of observed events (black markers) compared with the estimated backgrounds (filled histograms) in the validation signal-like region 2.

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Additional Figure 17:
The $M_{\mathrm{JJ}}$ distribution for the number of observed events (black markers) compared with the estimated backgrounds (filled histograms) in the validation signal-like region 2.

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Additional Figure 18:
Initial $R_{P/F}$ measured for the VS1 and VB1 region in the full RunII data and used in the signal region fit. Simulation prediction of the $\mathrm{t\bar{t}}$ distribution is subtracted from the combined observe data and a second order polynomial is fitted to the result.

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Additional Figure 19:
Initial $R_{P/F}$ measured for the VS2 and VB1 region in the full RunII data and used in the signal region fit. Simulation prediction of the $\mathrm{t\bar{t}}$ distribution is subtracted from the combined observe data and a second order polynomial is fitted to the result.

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Additional Figure 20:
The $R_{\text{Ratio}}$ for the SR1 after the validation fit.

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Additional Figure 21:
The $R_{\text{Ratio}}$ for the SR2 after the validation fit.

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Additional Figure 22:
The final transfer function, $R_{P/F}^{\text{init}}\times R_{\text{Ratio}}$, in the SR1 after the validation fit.

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Additional Figure 23:
The final transfer function, $R_{P/F}^{\text{init}}\times R_{\text{Ratio}}$, in the SR1 after the validation fit.

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Additional Figure 24:
The $M_{\mathrm{JY}}$ distribution for the number of observed events (black markers) compared with the estimated backgrounds (filled histograms) in the validation signal region 2. The distributions expected from the signal under three $M_{\mathrm{X}}$ and $M_{\mathrm{Y}}$ hypotheses and assuming a cross section of 1 fb are also shown.

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Additional Figure 25:
The $M_{\mathrm{JJ}}$ distribution for the number of observed events (black markers) compared with the estimated backgrounds (filled histograms) in the validation signal region 2. The distributions expected from the signal under three $M_{\mathrm{X}}$ and $M_{\mathrm{Y}}$ hypotheses and assuming a cross section of 1 fb are also shown.

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Additional Figure 26:
The softdrop mass distribution of the top-quark candidate jets in the 2016 semileptonic control region, loose ParticleNet category (CR L), after the joint semileptonic and hadronic signal region fit. Observed data (black markers) and the postfit estimate (filled histograms) are shown for the three jet categories.

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Additional Figure 27:
The softdrop mass distribution of the top-quark candidate jets in the 2016 semileptonic control region, tight ParticleNet category (CR T), after the joint semileptonic and hadronic signal region fit. Observed data (black markers) and the postfit estimate (filled histograms) are shown for the three jet categories.

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Additional Figure 28:
The softdrop mass distribution of the top-quark candidate jets in the 2017 semileptonic control region, loose ParticleNet category (CR L), after the joint semileptonic and hadronic signal region fit. Observed data (black markers) and the postfit estimate (filled histograms) are shown for the three jet categories.

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Additional Figure 29:
The softdrop mass distribution of the top-quark candidate jets in the 2017 semileptonic control region, tight ParticleNet category (CR T), after the joint semileptonic and hadronic signal region fit. Observed data (black markers) and the postfit estimate (filled histograms) are shown for the three jet categories.

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Additional Figure 30:
The softdrop mass distribution of the top-quark candidate jets in the 2018 semileptonic control region, loose ParticleNet category (CR L), after the joint semileptonic and hadronic signal region fit. Observed data (black markers) and the postfit estimate (filled histograms) are shown for the three jet categories.

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Additional Figure 31:
The softdrop mass distribution of the top-quark candidate jets in the 2018 semileptonic control region, tight ParticleNet category (CR T), after the joint semileptonic and hadronic signal region fit. Observed data (black markers) and the postfit estimate (filled histograms) are shown for the three jet categories.

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Additional Figure 32:
The 95% confidence level expected and observed limits on the signal cross-section as a function of $M_{\mathrm{X}}$ for different values of $M_{\mathrm{Y}}$. The red curves show the maximal possible cross sections of this process in NMSSM, taking into account all other theoretical and experimental constraints
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Compact Muon Solenoid
LHC, CERN