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| CMS-B2G-23-006 ; CERN-EP-2024-301 | ||
| Search for heavy neutral Higgs bosons A and H in the $ {\mathrm{t}\overline{\mathrm{t}}} $Z channel in proton-proton collisions at 13 TeV | ||
| CMS Collaboration | ||
| 30 November 2024 | ||
| Submitted to Phys. Lett. B | ||
| Abstract: A direct search for new heavy neutral Higgs bosons A and H in the $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{Z} $ channel is presented, targeting the process $ \mathrm{p}\mathrm{p}\to\mathrm{A}\to\mathrm{Z}\mathrm{H} $ with $ \mathrm{H}\to{\mathrm{t}\overline{\mathrm{t}}} $. For the first time, the channel with decays of the Z boson to muons or electrons in association with all-hadronic decays of the $ \mathrm{t} \overline{\mathrm{t}} $ system is targeted. The analysis uses proton-proton collision data collected at the CERN LHC with the CMS experiment at $ \sqrt{s}= $ 13 TeV, which correspond to an integrated luminosity of 138 fb$ ^{-1} $. No signal is observed. Upper limits on the product of the cross section and branching fractions are derived for narrow resonances A and H with masses up to 2100 and 2000 GeV, respectively, assuming A boson production through gluon fusion. The results are also interpreted within two-Higgs-doublet models, complementing and substantially extending the reach of previous searches. | ||
| Links: e-print arXiv:2412.00570 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Definition of the event categories. The five partitions shown apply to each of the classes of jet multiplicity (5j and $ \geq $6j), resulting in 10 categories per lepton flavour channel ($ \mu^{+}\mu^{-} $ or $ \mathrm{e}^+\mathrm{e}^- $). A value of 91 GeV is used for the Z boson mass $ m_{\mathrm{Z}} $ in the definition of the Z window. |
png pdf |
Figure 2:
Expected $ (\Delta m,p_{\mathrm{T}}^{\mathrm{Z}}) $ distribution for signal events with $ m_{\mathrm{A}}= $ 1000 GeV and $ m_{\mathrm{H}}= $ 350 GeV (red) and sum of backgrounds (blue) in the SR $ \geq $6j $ \geq $2b category, and boundaries of the elliptical bins (solid lines) used to construct the final observable. |
png pdf |
Figure 3:
Distributions of events in the $ p_{\mathrm{T}}^{\mathrm{Z}}\times\Delta m $ bins in the CRs after the fit to data described in Section 6 with a signal hypothesis of $ m_{\mathrm{A}}= $ 1000 GeV and $ m_{\mathrm{H}}= $ 350 (upper) and $ m_{\mathrm{H}}= $ 850 GeV (lower). The signal (solid red line) and background (coloured histograms) distributions are shown with their best fit normalizations from the simultaneous fit to the data (``post-fit''), where the sum of the $ \mu^{+}\mu^{-} $ and $ \mathrm{e}^+\mathrm{e}^- $ channels is shown for illustration purposes. In the left plot, the post-fit signal cross section is found to be 0.0 $ \pm $ 0.1 fb. Therefore, the corresponding histogram is not displayed. The signal is also shown for a normalization to 25 fb (``pre-fit'') in the dashed red line. The lower panels show the ratio of the observed data to the background events (black points with error bars) and the ratio of the total number of expected signal-plus-background events to the background events (red lines). In both panels, the hatched area represents the total uncertainty. |
png pdf |
Figure 3-a:
Distributions of events in the $ p_{\mathrm{T}}^{\mathrm{Z}}\times\Delta m $ bins in the CRs after the fit to data described in Section 6 with a signal hypothesis of $ m_{\mathrm{A}}= $ 1000 GeV and $ m_{\mathrm{H}}= $ 350 (upper) and $ m_{\mathrm{H}}= $ 850 GeV (lower). The signal (solid red line) and background (coloured histograms) distributions are shown with their best fit normalizations from the simultaneous fit to the data (``post-fit''), where the sum of the $ \mu^{+}\mu^{-} $ and $ \mathrm{e}^+\mathrm{e}^- $ channels is shown for illustration purposes. In the left plot, the post-fit signal cross section is found to be 0.0 $ \pm $ 0.1 fb. Therefore, the corresponding histogram is not displayed. The signal is also shown for a normalization to 25 fb (``pre-fit'') in the dashed red line. The lower panels show the ratio of the observed data to the background events (black points with error bars) and the ratio of the total number of expected signal-plus-background events to the background events (red lines). In both panels, the hatched area represents the total uncertainty. |
png pdf |
Figure 3-b:
Distributions of events in the $ p_{\mathrm{T}}^{\mathrm{Z}}\times\Delta m $ bins in the CRs after the fit to data described in Section 6 with a signal hypothesis of $ m_{\mathrm{A}}= $ 1000 GeV and $ m_{\mathrm{H}}= $ 350 (upper) and $ m_{\mathrm{H}}= $ 850 GeV (lower). The signal (solid red line) and background (coloured histograms) distributions are shown with their best fit normalizations from the simultaneous fit to the data (``post-fit''), where the sum of the $ \mu^{+}\mu^{-} $ and $ \mathrm{e}^+\mathrm{e}^- $ channels is shown for illustration purposes. In the left plot, the post-fit signal cross section is found to be 0.0 $ \pm $ 0.1 fb. Therefore, the corresponding histogram is not displayed. The signal is also shown for a normalization to 25 fb (``pre-fit'') in the dashed red line. The lower panels show the ratio of the observed data to the background events (black points with error bars) and the ratio of the total number of expected signal-plus-background events to the background events (red lines). In both panels, the hatched area represents the total uncertainty. |
png pdf |
Figure 4:
Distributions of $ p_{\mathrm{T}}^{\mathrm{Z}}\times\Delta m $ in the SRs after the fit to data with a signal hypothesis of $ m_{\mathrm{A}}= $ 1000 GeV and $ m_{\mathrm{H}}= $ 350 (upper) and $ m_{\mathrm{H}}= $ 850 GeV (lower). The signal (solid red line) and background (coloured histograms) distributions are shown with their best fit normalizations from the simultaneous fit to the data (``post-fit''), where the sum of the $ \mu^{+}\mu^{-} $ and $ \mathrm{e}^+\mathrm{e}^- $ channels is shown for illustration purposes. In the left plot, the post-fit signal cross section is found to be 0.0 $ \pm $ 0.1 fb. Therefore, the corresponding histogram is not displayed. The signal is also shown for a normalization to 25 fb (``pre-fit'') in the dashed red line. The lower panels show the ratio of the observed data to the background events (black points with error bars) and the ratio of the total number of expected signal-plus-background events to the background events (red lines). In both panels, the hatched area represents the total uncertainty. |
png pdf |
Figure 4-a:
Distributions of $ p_{\mathrm{T}}^{\mathrm{Z}}\times\Delta m $ in the SRs after the fit to data with a signal hypothesis of $ m_{\mathrm{A}}= $ 1000 GeV and $ m_{\mathrm{H}}= $ 350 (upper) and $ m_{\mathrm{H}}= $ 850 GeV (lower). The signal (solid red line) and background (coloured histograms) distributions are shown with their best fit normalizations from the simultaneous fit to the data (``post-fit''), where the sum of the $ \mu^{+}\mu^{-} $ and $ \mathrm{e}^+\mathrm{e}^- $ channels is shown for illustration purposes. In the left plot, the post-fit signal cross section is found to be 0.0 $ \pm $ 0.1 fb. Therefore, the corresponding histogram is not displayed. The signal is also shown for a normalization to 25 fb (``pre-fit'') in the dashed red line. The lower panels show the ratio of the observed data to the background events (black points with error bars) and the ratio of the total number of expected signal-plus-background events to the background events (red lines). In both panels, the hatched area represents the total uncertainty. |
png pdf |
Figure 4-b:
Distributions of $ p_{\mathrm{T}}^{\mathrm{Z}}\times\Delta m $ in the SRs after the fit to data with a signal hypothesis of $ m_{\mathrm{A}}= $ 1000 GeV and $ m_{\mathrm{H}}= $ 350 (upper) and $ m_{\mathrm{H}}= $ 850 GeV (lower). The signal (solid red line) and background (coloured histograms) distributions are shown with their best fit normalizations from the simultaneous fit to the data (``post-fit''), where the sum of the $ \mu^{+}\mu^{-} $ and $ \mathrm{e}^+\mathrm{e}^- $ channels is shown for illustration purposes. In the left plot, the post-fit signal cross section is found to be 0.0 $ \pm $ 0.1 fb. Therefore, the corresponding histogram is not displayed. The signal is also shown for a normalization to 25 fb (``pre-fit'') in the dashed red line. The lower panels show the ratio of the observed data to the background events (black points with error bars) and the ratio of the total number of expected signal-plus-background events to the background events (red lines). In both panels, the hatched area represents the total uncertainty. |
png pdf |
Figure 5:
Expected (left) and observed (right) 95% CL upper limits on the product of production cross section and branching fractions of the $ \mathrm{A}\to\mathrm{Z}\mathrm{H}\to\mathrm{Z}{\mathrm{t}\overline{\mathrm{t}}} $ process in the $ (m_{\mathrm{A}},\, m_{\mathrm{H}}) $ plane. |
png pdf |
Figure 5-a:
Expected (left) and observed (right) 95% CL upper limits on the product of production cross section and branching fractions of the $ \mathrm{A}\to\mathrm{Z}\mathrm{H}\to\mathrm{Z}{\mathrm{t}\overline{\mathrm{t}}} $ process in the $ (m_{\mathrm{A}},\, m_{\mathrm{H}}) $ plane. |
png pdf |
Figure 5-b:
Expected (left) and observed (right) 95% CL upper limits on the product of production cross section and branching fractions of the $ \mathrm{A}\to\mathrm{Z}\mathrm{H}\to\mathrm{Z}{\mathrm{t}\overline{\mathrm{t}}} $ process in the $ (m_{\mathrm{A}},\, m_{\mathrm{H}}) $ plane. |
png pdf |
Figure 6:
Median expected (dashed lines) and observed (filled contours) 95% CL exclusion regions in the $ (m_{\mathrm{H}},m_{\mathrm{A}}) $ parameter space of the type-II 2HDM for $ \tan\beta = $ 0.5 (blue), 1 (orange), and 1.5 (red), derived assuming narrow resonances. The enclosed regions are excluded. The dotted lines indicate points of constant total decay width $ \Gamma_{\mathrm{A}} $ of the A boson relative to its mass in the 2HDM, for the $ \tan\beta $ value of the corresponding colour. |
png pdf |
Figure 7:
Median expected (dashed lines) and observed (filled contours) 95% CL exclusion regions in the type-II 2HDM $ (\tan\beta, m_{\mathrm{A}}) $ parameter space at $ m_{\mathrm{H}}= $ 400 GeV (left) and in the $ (\tan\beta,\cos(\beta-\alpha)) $ parameter space at $ m_{\mathrm{A}}= $ 600 GeV and $ m_{\mathrm{H}}= $ 400 GeV (right), derived assuming narrow resonances. The enclosed regions are excluded. The dotted lines indicate points of constant total decay width $ \Gamma_{\mathrm{A}} $ of the A boson relative to its mass in the 2HDM. |
png pdf |
Figure 7-a:
Median expected (dashed lines) and observed (filled contours) 95% CL exclusion regions in the type-II 2HDM $ (\tan\beta, m_{\mathrm{A}}) $ parameter space at $ m_{\mathrm{H}}= $ 400 GeV (left) and in the $ (\tan\beta,\cos(\beta-\alpha)) $ parameter space at $ m_{\mathrm{A}}= $ 600 GeV and $ m_{\mathrm{H}}= $ 400 GeV (right), derived assuming narrow resonances. The enclosed regions are excluded. The dotted lines indicate points of constant total decay width $ \Gamma_{\mathrm{A}} $ of the A boson relative to its mass in the 2HDM. |
png pdf |
Figure 7-b:
Median expected (dashed lines) and observed (filled contours) 95% CL exclusion regions in the type-II 2HDM $ (\tan\beta, m_{\mathrm{A}}) $ parameter space at $ m_{\mathrm{H}}= $ 400 GeV (left) and in the $ (\tan\beta,\cos(\beta-\alpha)) $ parameter space at $ m_{\mathrm{A}}= $ 600 GeV and $ m_{\mathrm{H}}= $ 400 GeV (right), derived assuming narrow resonances. The enclosed regions are excluded. The dotted lines indicate points of constant total decay width $ \Gamma_{\mathrm{A}} $ of the A boson relative to its mass in the 2HDM. |
| Summary |
| A direct search for heavy neutral Higgs bosons A and H in the $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{Z} $ channel has been conducted, using proton-proton collision data collected by the CMS experiment at $ \sqrt{s}= $ 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The search targets the process $ \mathrm{p}\mathrm{p}\to\mathrm{A}\to\mathrm{Z}\mathrm{H} $ with $ \mathrm{H}\to{\mathrm{t}\overline{\mathrm{t}}} $. For the first time, the final state with decays of the Z boson to muons or electrons in association with all-hadronic decays of the $ \mathrm{t} \overline{\mathrm{t}} $ system is considered. No evidence for a signal is observed. Stringent upper limits are set on the product of the cross section and branching fractions for A and H boson masses up to $ m_{\mathrm{A}}= $ 2100 GeV and $ m_{\mathrm{H}}= $ 2000 GeV, respectively, assuming narrow resonances. The results are further used to constrain the parameter space of two-Higgs-doublet models as a function of the $ \tan\beta $ and $ \cos(\beta-\alpha) $ parameters. The excess of events reported by the ATLAS Collaboration in the region around $ (m_{\mathrm{A}},\, m_{\mathrm{H}}) = $ (650,450) GeV with a local significance of 2.85 standard deviations [22] is not observed in the search presented here, which has similar expected sensitivity. The results complement and substantially extend the reach of previous searches, constraining parameter regions relevant for models explaining baryogenesis. |
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