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| CMS-HIG-18-012 ; CERN-EP-2019-254 | ||
| Search for new neutral Higgs bosons through the $\mathrm{H} \to Z \mathrm{A} \to \ell^{+}\ell^{-} \mathrm{b\bar{b}}$ process in pp collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 9 November 2019 | ||
| JHEP 03 (2020) 055 | ||
| Abstract: This paper reports on a search for an extended scalar sector of the standard model, where a new CP-even (odd) boson decays to a Z boson and a lighter CP-odd (even) boson, and the latter further decays to a b quark pair. The Z boson is reconstructed via its decays to electron or muon pairs. The analysed data were recorded in proton-proton collisions at a center-of-mass energy $\sqrt{s} = $ 13 TeV, collected by the CMS experiment at the LHC during 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Data and predictions from the standard model are in agreement within the uncertainties. Upper limits at 95% confidence level are set on the production cross section times branching fraction, with masses of the new bosons up to 1000 GeV. The results are interpreted in the context of the two-Higgs-doublet model. | ||
| Links: e-print arXiv:1911.03781 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Possible 2HDM mass hierarchies: conventional, where A is degenerate in mass with the charged scalars; and twisted [9], where H is degenerate in mass with the charged scalars. In both scenarios, the lighter boson between A and H can be either heavier or lighter than the observed Higgs boson H(125). |
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Figure 2:
The H and A branching fractions as a function of $\cos(\beta - \alpha)$ in Type-II 2HDM for the following set of parameters: $\tan\beta = $ 1.5, $ {{m}_{\mathrm{H}}} = $ 300 GeV, $ {{m}_{\mathrm{A} }} = $ 200 GeV (left). The H and A branching fractions as a function of $\tan\beta $ in Type-II 2HDM for the following set of parameters: $\cos(\beta - \alpha) = $ 0.01, $ {{m}_{\mathrm{H}}} = $ 300 GeV and $ {{m}_{\mathrm{A} }} = $ 200 GeV (right). |
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Figure 3:
The $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ (left) and $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ (right) distributions in data and background events after requiring all the analysis selections, for $\mu \mu $+ee events. The background shapes and normalisations are obtained from simulation. The various signal hypotheses displayed have been scaled to a cross section of 1 pb for illustrative purposes. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties prior to the fit (introduced in Section 6). |
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Figure 3-a:
The $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ distribution in data and background events after requiring all the analysis selections, for $\mu \mu $+ee events. The background shapes and normalisations are obtained from simulation. The various signal hypotheses displayed have been scaled to a cross section of 1 pb for illustrative purposes. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties prior to the fit (introduced in Section 6). |
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Figure 3-b:
The $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ distribution in data and background events after requiring all the analysis selections, for $\mu \mu $+ee events. The background shapes and normalisations are obtained from simulation. The various signal hypotheses displayed have been scaled to a cross section of 1 pb for illustrative purposes. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties prior to the fit (introduced in Section 6). |
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Figure 4:
The $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ vs. $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ plane for signal samples under three different mass hypotheses, on which the parametrised ellipses are shown (left). A signal hypothesis with ${{m}_{\mathrm{H}}} =$ 500 GeV and ${{m}_{\mathrm{A} }} =$ 300GeV is shown in the $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ vs. $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ plane (right). The different ellipses show the variation of the $\rho $ parameter in steps of 0.5, from 0 to 3. The intensity of the color in each hexagonal bin is proportional to the number of events in it. |
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Figure 4-a:
The $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ vs. $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ plane for signal samples under three different mass hypotheses, on which the parametrised ellipses are shown. The intensity of the color in each hexagonal bin is proportional to the number of events in it. |
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Figure 4-b:
A signal hypothesis with ${{m}_{\mathrm{H}}} =$ 500 GeV and ${{m}_{\mathrm{A} }} =$ 300GeV is shown in the $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ vs. $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ plane. The different ellipses show the variation of the $\rho $ parameter in steps of 0.5, from 0 to 3. The intensity of the color in each hexagonal bin is proportional to the number of events in it. |
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Figure 5:
Post-fit $\rho $ distributions from a background-only fit for the same-flavour lepton (left) and mixed-flavour lepton (right) events corresponding to a signal hypothesis with ${{m}_{\mathrm{H}}} = $ 261 GeV and ${{m}_{\mathrm{A} }} =$ 150 GeV (upper) and ${{m}_{\mathrm{H}}} =$ 442 GeV and ${{m}_{\mathrm{A} }} =$ 193 GeV (lower). The signal is normalised to 1 pb. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties after the fit. |
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Figure 5-a:
Post-fit $\rho $ distribution from a background-only fit for the same-flavour lepton events corresponding to a signal hypothesis with ${{m}_{\mathrm{H}}} = $ 261 GeV and ${{m}_{\mathrm{A} }} =$ 150 GeV. The signal is normalised to 1 pb. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties after the fit. |
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Figure 5-b:
Post-fit $\rho $ distribution from a background-only fit for the mixed-flavour lepton events corresponding to a signal hypothesis with ${{m}_{\mathrm{H}}} = $ 261 GeV and ${{m}_{\mathrm{A} }} =$ 150 GeV. The signal is normalised to 1 pb. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties after the fit. |
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Figure 5-c:
Post-fit $\rho $ distribution from a background-only fit for the same-flavour lepton events corresponding to a signal hypothesis with ${{m}_{\mathrm{H}}} =$ 442 GeV and ${{m}_{\mathrm{A} }} =$ 193 GeV. The signal is normalised to 1 pb. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties after the fit. |
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Figure 5-d:
Post-fit $\rho $ distribution from a background-only fit for the mixed-flavour lepton events corresponding to a signal hypothesis with ${{m}_{\mathrm{H}}} =$ 442 GeV and ${{m}_{\mathrm{A} }} =$ 193 GeV. The signal is normalised to 1 pb. Error bars indicate statistical uncertainties, while shaded bands show systematic uncertainties after the fit. |
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Figure 6:
Distribution of the local p-value in the $ {m_{\ell \ell {\mathrm{j}} {\mathrm{j}}}} $ vs. $ {m_{{\mathrm{j}} {\mathrm{j}}}} $ plane. |
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Figure 7:
Observed 95% CL upper limits on the product of the production cross section and branching fraction $\sigma \mathcal {B}$ for $\mathrm{H} (\mathrm{A} ) \to Z \mathrm{A} (\mathrm{H}) \to \ell \ell \mathrm{b} \mathrm{\bar{b}} $ as a function of ${{m}_{\mathrm{A} }}$ and ${{m}_{\mathrm{H}}}$. The limits are computed using the asymptotic CLs method, combining the ee and $\mu\mu$ channels. |
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Figure 8:
Expected and observed 95% CL exclusion contours for the Type-II 2HDM benchmark $\tan\beta =$ 1.5 and $\cos(\beta -\alpha)=$ 0.01 as a function of ${{m}_{\mathrm{A} }}$ and ${{m}_{\mathrm{H}}}$. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of the exclusion contours expected under the background-only hypothesis. The limits are computed using the asymptotic CLs method, combining the ee and $\mu\mu$ channels. |
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Figure 9:
Expected and observed 95% CL exclusion contours for ${{m}_{\mathrm{H}}} =$ 379 GeV and ${{m}_{\mathrm{A} }} =$ 172 GeV as a function of $\tan\beta $ and ${\cos(\beta - \alpha)}$. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of the exclusion contours expected under the background-only hypothesis. The limits are computed using the asymptotic CLs method, combining the ee and $\mu\mu$ channels. |
| Tables | |
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Table 1:
Expected and observed event yields prior to the fit in the signal region with ${{m}_{\mathrm{H}}} =$ 500 GeV and ${{m}_{\mathrm{A} }} =$ 200 GeV for each elliptical bin. The signal is normalised to its theoretical cross section for the Type-II 2HDM benchmark $\tan\beta =$ 1.5 and $\cos(\beta - \alpha)=$ 0.01. The ee and $\mu\mu$ categories are summed. |
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Table 2:
Summary of the systematic uncertainties prior to the fit and the variation, in percentages, that they induce on the total event yields for the dominant background and signal processes, under a particular signal hypothesis with ${{m}_{\mathrm{H}}} = $ 379 GeV and ${{m}_{\mathrm{A} }} = $ 172 GeV. |
| Summary |
|
This paper reports on a search for a new CP-even (odd) neutral Higgs boson, decaying into a Z boson and a lighter CP-odd (even) neutral Higgs boson, where the Z decays into an electron or muon pair, and the light Higgs boson into a b quark pair. The search is based on LHC proton-proton collision data at a center-of-mass energy $\sqrt{s}=$ 13 TeV collected by the CMS experiment during 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. We consider decays such as $\mathrm{H} \to \mathrm{Z}\mathrm{A} \to \ell\ell\mathrm{b\bar{b}}$, where H and A are the additional CP-even and -odd Higgs bosons above-mentioned, respectively, in the context of the two-Higgs-doublet model (2HDM). They are searched for in the mass range from 120 to 1000 GeV for H and 30 to 1000 GeV for A. The search is subsequently extended to the $\mathrm{A} \to \mathrm{Z}\mathrm{H} \to \ell\ell\mathrm{b\bar{b}}$ process via interchanging the two mass parameters. No significant deviations from the standard model expectations are observed. Model independent upper limits on the product of cross section and branching fraction are set. Limits are also set on the parameters of the 2HDM, assuming the Type-II formulation. Under the specific benchmark scenario corresponding to $\tan\beta=$ 1.5 and $\cos (\beta - \alpha)=$ 0.01, regions with ${{m}_{\mathrm{H}}}$ in the range 150-700 GeV and ${{m}_{\mathrm{A} }}$ in the range 30-295 GeV with ${{m}_{\mathrm{H}}} > {{m}_{\mathrm{A} }} $, or alternatively for ${{m}_{\mathrm{H}}}$ in the range 30-280 GeV and ${{m}_{\mathrm{A} }}$ in the range 150-700 GeV with ${{m}_{\mathrm{H}}} < {{m}_{\mathrm{A} }} $ are excluded at 95% confidence level. Results are also interpreted in the scenario where ${{m}_{\mathrm{H}}} =$ 379 GeV and ${{m}_{\mathrm{A} }} =$ 172 GeV. In this context, the region with $\cos (\beta - \alpha)$ in the range $-$0.9-0.3 and $\tan\beta$ in the range 0.5-7.0 is excluded at 95% confidence level. With respect to previous searches, a larger region of the Type-II 2HDM parameter space is excluded. |
| Additional Material: Signal Efficiencies |
|
JASON files of signal efficiencies : MuMu channel, ElEl channel. In each file: First column: mA; Second column: mH; Third column: signal efficiency. |
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