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CMS-PAS-B2G-17-006
Search for heavy resonances decaying into two Higgs bosons or into a Higgs and a vector boson in proton-proton collisions at 13 TeV
Abstract: A search is presented for massive resonances decaying either into two Higgs (H) bosons or into a Higgs and a vector (V = W or Z) boson. The decay channels considered are $\mathrm{VH} \rightarrow q\bar{q}\tau^{+}\tau^{-}$ and $\mathrm{HH} \rightarrow b\bar{b}\tau^{+}\tau^{-}$. This analysis is based on the data sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV by the CMS Collaboration in 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. For the high-mass resonances considered ($\geq $ 1 TeV), substructure techniques are employed to differentiate between the hadronization products of a vector boson decaying to quarks, a Higgs boson decaying to bottom quarks, and quark- or gluon-induced jets. Due to the large boost of the Higgs boson, the two leptons in the $H \rightarrow \tau^{+}\tau^{-}$ decay are collimated. Advanced techniques are used for events in which one $\tau$ lepton decays hadronically and the other leptonically, and in which both decay hadronically. Upper limits at 95% confidence level are set on the product of cross section times branching fraction for resonance masses between 900 and 4000 GeV, ranging from 100 to 6 fb for spin 0 and 2 resonances, and from 250 to 6 fb for spin 1 resonances.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Feynman diagrams for the production of a heavy vector boson V' (W' or Z') that decays to a vector boson and a Higgs boson (left) and the production of a spin-0 radion or a spin-2 graviton that decays to a Higgs boson pair (right).

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Figure 1-a:
Feynman diagrams for the production of a heavy vector boson V' (W' or Z') that decays to a vector boson and a Higgs boson.

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Figure 1-b:
Feynman diagrams for the production of a spin-0 radion or a spin-2 graviton that decays to a Higgs boson pair.

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Figure 2:
Fit to data for the $\tau _{21}$ HP $\ell \tau _{h}$ channel of the softdrop mass distribution in order to determine the background normalization (left) and to the resonance mass spectrum in order to determine the background shape in the sidebands (right).

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Figure 2-a:
Fit to data for the $\tau _{21}$ HP $\ell \tau _{h}$ channel of the softdrop mass distribution in order to determine the background normalization.

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Figure 2-b:
Fit to the resonance mass spectrum in order to determine the background shape in the sidebands.

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Figure 3:
Data and expected backgrounds determined with the $\alpha $ transfer function method in the $\ell \tau _{h}$ channel: W mass window for the $\tau _{21}$ HP (upper left) and LP (upper right) categories, Z mass window for the $\tau _{21}$ HP (middle left) and LP (middle right) categories, and H mass window for the 1 b tagged subjet (lower left) and 2 b tagged subjets (lower right) categories. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} =$ 1 for the radion, each with a mass of 2 TeV.

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Figure 3-a:
Data and expected backgrounds determined with the $\alpha $ transfer function method in the $\ell \tau _{h}$ channel: W mass window for the $\tau _{21}$ HP category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} =$ 1 for the radion, each with a mass of 2 TeV.

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Figure 3-b:
Data and expected backgrounds determined with the $\alpha $ transfer function method in the $\ell \tau _{h}$ channel: W mass window for the $\tau _{21}$ LP category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} =$ 1 for the radion, each with a mass of 2 TeV.

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Figure 3-c:
Data and expected backgrounds determined with the $\alpha $ transfer function method in the $\ell \tau _{h}$ channel: Z mass window for the $\tau _{21}$ HP (middle right) category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} =$ 1 for the radion, each with a mass of 2 TeV.

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Figure 3-d:
Data and expected backgrounds determined with the $\alpha $ transfer function method in the $\ell \tau _{h}$ channel: Z mass window for the $\tau _{21}$ LP (middle right) category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} =$ 1 for the radion, each with a mass of 2 TeV.

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Figure 3-e:
Data and expected backgrounds determined with the $\alpha $ transfer function method in the $\ell \tau _{h}$ channel: H mass window for the 1 b tagged subjet category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} =$ 1 for the radion, each with a mass of 2 TeV.

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Figure 3-f:
Data and expected backgrounds determined with the $\alpha $ transfer function method in the $\ell \tau _{h}$ channel: H mass window for the 2 b tagged subjets category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} =$ 1 for the radion, each with a mass of 2 TeV.

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Figure 4:
Data and expected background determined with the $\alpha $ transfer function method in the $\tau _{h}\tau _{h}$ channel: W mass window for the $\tau _{21}$ HP (upper left) and LP (upper right) categories, Z mass window for the $\tau _{21}$ HP (middle left) and LP (middle right) categories, and H mass window for the 1 b-tagged subjet (lower left) and 2 b-tagged subjets (lower right) categories. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} = $ 1 for the radion, each with a mass of 2 TeV.

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Figure 4-a:
Data and expected background determined with the $\alpha $ transfer function method in the $\tau _{h}\tau _{h}$ channel: W mass window for the $\tau _{21}$ HP category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} = $ 1 for the radion, each with a mass of 2 TeV.

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Figure 4-b:
Data and expected background determined with the $\alpha $ transfer function method in the $\tau _{h}\tau _{h}$ channel: W mass window for the $\tau _{21}$ LP category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} = $ 1 for the radion, each with a mass of 2 TeV.

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Figure 4-c:
Data and expected background determined with the $\alpha $ transfer function method in the $\tau _{h}\tau _{h}$ channel: Z mass window for the $\tau _{21}$ HP category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} = $ 1 for the radion, each with a mass of 2 TeV.

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Figure 4-d:
Data and expected background determined with the $\alpha $ transfer function method in the $\tau _{h}\tau _{h}$ channel: Z mass window for the $\tau _{21}$ LP category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} = $ 1 for the radion, each with a mass of 2 TeV.

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Figure 4-e:
Data and expected background determined with the $\alpha $ transfer function method in the $\tau _{h}\tau _{h}$ channel: H mass window for the 1 b-tagged subjet category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} = $ 1 for the radion, each with a mass of 2 TeV.

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Figure 4-f:
Data and expected background determined with the $\alpha $ transfer function method in the $\tau _{h}\tau _{h}$ channel: H mass window for the 2 b-tagged subjets category. Signal contributions are also shown assuming the benchmark scenario B of the HVT model for the V' and ${\lambda}_{R} = $ 1 for the radion, each with a mass of 2 TeV.

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Figure 5:
Observed 95% CL upper limits on $\sigma \times $BR(X$\rightarrow $WH) (left) and $\sigma \times $BR(Z$\rightarrow $ZH) (right). Expected limits are shown with 1 and 2$\sigma $ uncertainty bands. The $\ell \tau _{h}$ and $\tau _{h}\tau _{h}$ final states, HP and LP $\tau _{21}$ categories, and W and Z mass signal regions are combined.

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Figure 5-a:
Observed 95% CL upper limits on $\sigma \times $BR(X$\rightarrow $WH). Expected limits are shown with 1 and 2$\sigma $ uncertainty bands. The $\ell \tau _{h}$ and $\tau _{h}\tau _{h}$ final states, HP and LP $\tau _{21}$ categories, and W and Z mass signal regions are combined.

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Figure 5-b:
Observed 95% CL upper limits on $\sigma \times $BR(Z$\rightarrow $ZH). Expected limits are shown with 1 and 2$\sigma $ uncertainty bands. The $\ell \tau _{h}$ and $\tau _{h}\tau _{h}$ final states, HP and LP $\tau _{21}$ categories, and W and Z mass signal regions are combined.

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Figure 6:
Observed 95% CL upper limits on $\sigma \times $BR(X(spin-0)$\rightarrow $HH) (left) and $\sigma \times $BR(X(spin-2)$\rightarrow $HH) (right). Expected limits are shown with 1 and 2$\sigma $ uncertainty bands. The $\ell \tau _{h}$ and $\tau _{h}\tau _{h}$ final states, and 1 and 2 sub-jet b-tag categories are combined.

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Figure 6-a:
Observed 95% CL upper limits on $\sigma \times $BR(X(spin-0)$\rightarrow $HH). Expected limits are shown with 1 and 2$\sigma $ uncertainty bands. The $\ell \tau _{h}$ and $\tau _{h}\tau _{h}$ final states, and 1 and 2 sub-jet b-tag categories are combined.

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Figure 6-b:
Observed 95% CL upper limits on $\sigma \times $BR(X(spin-2)$\rightarrow $HH). Expected limits are shown with 1 and 2$\sigma $ uncertainty bands. The $\ell \tau _{h}$ and $\tau _{h}\tau _{h}$ final states, and 1 and 2 sub-jet b-tag categories are combined.

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Figure 7:
Expected (with $ \pm 1 (2) \sigma $ bands) and observed 95% CL upper limit on $\sigma \times $BR(X$\rightarrow $VH) (left) in the $\ell \tau _{h}$ and $\tau _{h}\tau _{h}$, $\tau _{21}$ HP and LP categories, with W and Z mass signal regions combined. Observed exclusion limit (right) in the space of the HVT model parameters $[ g_{V} c_{H}, g^2 c_{F}/g_{V}]$, described in the text, for three different mass hypotheses (1.5, 2, and 3 TeV). The region of parameter space where the natural resonance width is larger than the typical experimental resolution of 7%, for which the narrow width assumption is not valid, is shaded in grey.

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Figure 7-a:
Expected (with $ \pm 1 (2) \sigma $ bands) and observed 95% CL upper limit on $\sigma \times $BR(X$\rightarrow $VH) in the $\ell \tau _{h}$ and $\tau _{h}\tau _{h}$, $\tau _{21}$ HP and LP categories, with W and Z mass signal regions combined.

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Figure 7-b :
Observed exclusion limit in the space of the HVT model parameters $[ g_{V} c_{H}, g^2 c_{F}/g_{V}]$, described in the text, for three different mass hypotheses (1.5, 2, and 3 TeV). The region of parameter space where the natural resonance width is larger than the typical experimental resolution of 7%, for which the narrow width assumption is not valid, is shaded in grey.
Tables

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Table 1:
Normalization scale factors for top quark production for different event categories. Uncertainties are due to the limited size of data statistics in the control regions and the uncertainty on the b tagging efficiency.

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Table 2:
Predicted number of background events and observed number of events in the signal region, for all event categories. W, Z and H regions are intervals in the jet softdrop mass distribution that range from 65 GeV to 85 GeV, from 85 GeV to 105 GeV, and from 105 GeV to 135 GeV respectively. Separate sources of uncertainty in the expected number are reported: the statistical uncertainty on the V+jet contribution from the fit procedure (fit), the one due to the difference between the nominal and alternative function chosen for the fit (alt), and the top background uncertainty from the fit to the simulated jet mass spectrum.

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Table 3:
Summary of systematic uncertainties for the background and signal samples. Uncertainties marked with $\dagger $ are not included in the limit bands, but instead reported in the theory band.
Summary
A search has been conducted for heavy resonances, with masses between 900 GeV and 4 TeV, and which couple more strongly to bosons than fermions. The heavy particle is searched for in final states with two bosons: one of which is a W, Z, or H boson that decays hadronically; while the other is a Higgs boson that decays to a pair of tau leptons. The analyzed data are collected by the CMS experiment at $\sqrt{s}= $ 13 TeV during 2016 operations, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Depending on the resonance mass, expected upper limits on the production cross section times branching ratios to WH, ZH, and HH, for spin-1, spin-0, and spin-2 resonances are set between 250 and 6 fb.
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Compact Muon Solenoid
LHC, CERN