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| CMS-NPS-25-003 ; CERN-EP-2026-133 | ||
| Search for Higgs boson decays into two neutral scalars with unequal masses in final states with b quarks and tau leptons in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 18 May 2026 | ||
| Submitted to the Journal of High Energy Physics | ||
| Abstract: A search for Higgs boson (H) decays into a pair of neutral scalars $ \phi_{1} $ and $ \phi_{2} $, with $ \phi_{2} $ heavier than $ \phi_{1} $, is performed in final states with b quarks and tau leptons. Depending on the masses of the neutral scalars, $ \phi_{2} $ can undergo a cascade decay into $ \phi_{1} \phi_{1} $. For both the cascade and non-cascade scenarios, one $ \phi_{1} $ is required to decay to a pair of tau leptons. Proton-proton collision data corresponding to an integrated luminosity of 138 fb$^{-1}$ collected with the CMS detector at the LHC at $ \sqrt{s}= $ 13 TeV are analyzed. No statistically significant excess over the standard model expectation is observed. Upper limits are set on the products $ \sigma \mathcal{B}(\mathrm{H} \to \phi_{1} \phi_{2} \to 3\phi_{1} \to 2\tau 4\mathrm{b}) $ and $ \sigma \mathcal{B}(\mathrm{H} \to \phi_{1} \phi_{2})\mathcal{B}(\phi_{1} \to 2\tau)\mathcal{B}(\phi_{2} \to 2\mathrm{b}) $ where $ \sigma $ is the Higgs boson production cross section. The observed upper limits range between 0.9 and 36.8 pb at 95% confidence level, depending on the mass hypothesis and decay scenario. | ||
| Links: e-print arXiv:2605.19144 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Representative schematic diagrams showing the $ {\mathrm{g}\mathrm{g}} $F (upper) and VBF (lower) production of the Higgs boson decaying to 2 $ \tau4\mathrm{b} $ (cascade, left) and 2 $ \tau2\mathrm{b} $ (non-cascade, right) final states. |
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Figure 1-a:
Representative schematic diagrams showing the $ {\mathrm{g}\mathrm{g}} $F (upper) and VBF (lower) production of the Higgs boson decaying to 2 $ \tau4\mathrm{b} $ (cascade, left) and 2 $ \tau2\mathrm{b} $ (non-cascade, right) final states. |
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Figure 1-b:
Representative schematic diagrams showing the $ {\mathrm{g}\mathrm{g}} $F (upper) and VBF (lower) production of the Higgs boson decaying to 2 $ \tau4\mathrm{b} $ (cascade, left) and 2 $ \tau2\mathrm{b} $ (non-cascade, right) final states. |
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Figure 1-c:
Representative schematic diagrams showing the $ {\mathrm{g}\mathrm{g}} $F (upper) and VBF (lower) production of the Higgs boson decaying to 2 $ \tau4\mathrm{b} $ (cascade, left) and 2 $ \tau2\mathrm{b} $ (non-cascade, right) final states. |
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Figure 1-d:
Representative schematic diagrams showing the $ {\mathrm{g}\mathrm{g}} $F (upper) and VBF (lower) production of the Higgs boson decaying to 2 $ \tau4\mathrm{b} $ (cascade, left) and 2 $ \tau2\mathrm{b} $ (non-cascade, right) final states. |
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Figure 2:
Pre-fit distributions of $ D_{\zeta} $ (upper left), $ m^{\text{vis}}(\tau\tau\mathrm{b}_1) $ (upper right), $ m_{\mathrm{T}}(\mu, p_{\mathrm{T}}^\text{miss}) $ (lower left), and $ m_{\mathrm{T}}(\tau_\mathrm{h}, p_{\mathrm{T}}^\text{miss}) $ (lower right), including underflow and overflow bins, for preselected events with at least one b-tagged jet for the $ \mu\tau_\mathrm{h} $ channel, without any SR requirements. The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The combination of statistical and shape systematic uncertainties is displayed with the hatched areas. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower panel of each plot shows the ratio of the data to the sum of the predicted number of background events. The vertical bars on the points show the statistical uncertainty in the ratio. |
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Figure 2-a:
Pre-fit distributions of $ D_{\zeta} $ (upper left), $ m^{\text{vis}}(\tau\tau\mathrm{b}_1) $ (upper right), $ m_{\mathrm{T}}(\mu, p_{\mathrm{T}}^\text{miss}) $ (lower left), and $ m_{\mathrm{T}}(\tau_\mathrm{h}, p_{\mathrm{T}}^\text{miss}) $ (lower right), including underflow and overflow bins, for preselected events with at least one b-tagged jet for the $ \mu\tau_\mathrm{h} $ channel, without any SR requirements. The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The combination of statistical and shape systematic uncertainties is displayed with the hatched areas. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower panel of each plot shows the ratio of the data to the sum of the predicted number of background events. The vertical bars on the points show the statistical uncertainty in the ratio. |
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Figure 2-b:
Pre-fit distributions of $ D_{\zeta} $ (upper left), $ m^{\text{vis}}(\tau\tau\mathrm{b}_1) $ (upper right), $ m_{\mathrm{T}}(\mu, p_{\mathrm{T}}^\text{miss}) $ (lower left), and $ m_{\mathrm{T}}(\tau_\mathrm{h}, p_{\mathrm{T}}^\text{miss}) $ (lower right), including underflow and overflow bins, for preselected events with at least one b-tagged jet for the $ \mu\tau_\mathrm{h} $ channel, without any SR requirements. The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The combination of statistical and shape systematic uncertainties is displayed with the hatched areas. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower panel of each plot shows the ratio of the data to the sum of the predicted number of background events. The vertical bars on the points show the statistical uncertainty in the ratio. |
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Figure 2-c:
Pre-fit distributions of $ D_{\zeta} $ (upper left), $ m^{\text{vis}}(\tau\tau\mathrm{b}_1) $ (upper right), $ m_{\mathrm{T}}(\mu, p_{\mathrm{T}}^\text{miss}) $ (lower left), and $ m_{\mathrm{T}}(\tau_\mathrm{h}, p_{\mathrm{T}}^\text{miss}) $ (lower right), including underflow and overflow bins, for preselected events with at least one b-tagged jet for the $ \mu\tau_\mathrm{h} $ channel, without any SR requirements. The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The combination of statistical and shape systematic uncertainties is displayed with the hatched areas. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower panel of each plot shows the ratio of the data to the sum of the predicted number of background events. The vertical bars on the points show the statistical uncertainty in the ratio. |
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Figure 2-d:
Pre-fit distributions of $ D_{\zeta} $ (upper left), $ m^{\text{vis}}(\tau\tau\mathrm{b}_1) $ (upper right), $ m_{\mathrm{T}}(\mu, p_{\mathrm{T}}^\text{miss}) $ (lower left), and $ m_{\mathrm{T}}(\tau_\mathrm{h}, p_{\mathrm{T}}^\text{miss}) $ (lower right), including underflow and overflow bins, for preselected events with at least one b-tagged jet for the $ \mu\tau_\mathrm{h} $ channel, without any SR requirements. The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The combination of statistical and shape systematic uncertainties is displayed with the hatched areas. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower panel of each plot shows the ratio of the data to the sum of the predicted number of background events. The vertical bars on the points show the statistical uncertainty in the ratio. |
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Figure 3:
Pre-fit BDT score distribution for preselected events with at least one b-tagged jet for the $ \mu\tau_\mathrm{h} $ (upper left), $ \mathrm{e}\tau_\mathrm{h} $ (upper right), and $ \mathrm{e}\mu $ (lower) channels, without any SR requirements. The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The combination of statistical and shape systematic uncertainties is displayed with the hatched areas. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower panel of each plot shows the ratio of the data to the sum of the predicted number of background events. The vertical bars on the points show the statistical uncertainty in the ratio. |
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Figure 3-a:
Pre-fit BDT score distribution for preselected events with at least one b-tagged jet for the $ \mu\tau_\mathrm{h} $ (upper left), $ \mathrm{e}\tau_\mathrm{h} $ (upper right), and $ \mathrm{e}\mu $ (lower) channels, without any SR requirements. The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The combination of statistical and shape systematic uncertainties is displayed with the hatched areas. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower panel of each plot shows the ratio of the data to the sum of the predicted number of background events. The vertical bars on the points show the statistical uncertainty in the ratio. |
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Figure 3-b:
Pre-fit BDT score distribution for preselected events with at least one b-tagged jet for the $ \mu\tau_\mathrm{h} $ (upper left), $ \mathrm{e}\tau_\mathrm{h} $ (upper right), and $ \mathrm{e}\mu $ (lower) channels, without any SR requirements. The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The combination of statistical and shape systematic uncertainties is displayed with the hatched areas. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower panel of each plot shows the ratio of the data to the sum of the predicted number of background events. The vertical bars on the points show the statistical uncertainty in the ratio. |
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Figure 3-c:
Pre-fit BDT score distribution for preselected events with at least one b-tagged jet for the $ \mu\tau_\mathrm{h} $ (upper left), $ \mathrm{e}\tau_\mathrm{h} $ (upper right), and $ \mathrm{e}\mu $ (lower) channels, without any SR requirements. The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The combination of statistical and shape systematic uncertainties is displayed with the hatched areas. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower panel of each plot shows the ratio of the data to the sum of the predicted number of background events. The vertical bars on the points show the statistical uncertainty in the ratio. |
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Figure 4:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 4-a:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 4-b:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 4-c:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 4-d:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 4-e:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 4-f:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 5:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure 5-a:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure 5-b:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 5-c:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure 5-d:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 5-e:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 5-f:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), SR3 (middle left), and SR4 (middle right), and in events with at least two b-tagged jets: SR1 (lower left) and SR2 (lower right). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 6:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\mu $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), and SR3 (middle left), and in events with at least two b-tagged jets: SR1 (middle right) and SR2 (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 6-a:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\mu $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), and SR3 (middle left), and in events with at least two b-tagged jets: SR1 (middle right) and SR2 (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure 6-b:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\mu $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), and SR3 (middle left), and in events with at least two b-tagged jets: SR1 (middle right) and SR2 (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure 6-c:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\mu $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), and SR3 (middle left), and in events with at least two b-tagged jets: SR1 (middle right) and SR2 (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure 6-d:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\mu $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), and SR3 (middle left), and in events with at least two b-tagged jets: SR1 (middle right) and SR2 (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure 6-e:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\mu $ channel, in events with exactly one b-tagged jet: SR1 (upper left), SR2 (upper right), and SR3 (middle left), and in events with at least two b-tagged jets: SR1 (middle right) and SR2 (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
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Figure 7:
The observed (points) and median expected (dotted line) 95% CL upper limits on the product $ \sigma \mathrm{B_{C}} $ for the cascade scenario using the BDT-based event categorization and the fit to the $ m_{\tau\tau} $ distribution, for different mass hypotheses ($ m_{\phi_{1}} $, $ m_{\phi_{2}} $). The horizontal bars on the points are for better legibility only. The green and yellow regions show the 68 and 95% expected range for the median value, respectively. |
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Figure 8:
The observed (points) and median expected (dotted line) 95% CL upper limits on the product $ \sigma \mathrm{B_{NC}} $ for the non-cascade scenario using the BDT-based event categorization and the fit to the $ m_{\tau\tau} $ distribution, for different mass hypotheses ($ m_{\phi_{1}} $, $ m_{\phi_{2}} $). The horizontal bars on the points are for better legibility only. The green and yellow regions show the 68 and 95% expected range for the median value, respectively. |
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Figure 9:
The 95% CL upper limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $, obtained using the BDT-based event categorization, as a function of the scalar masses $ m_{\phi_{1}} $ and $ m_{\phi_{2}} $. For the ($ \phi_{1} $, $ \phi_{2} $) mass hypotheses (15, 30), (20, 40), and (30, 60) GeV, only the non-cascade limits are shown. For all other mass hypotheses, either cascade or non-cascade limits are presented, depending on whether the cascade decay is kinematically allowed ($ m_{\phi_{2}} \geq 2 m_{\phi_{1}} $). The numbers displayed in the plot are in \unitpb. |
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Figure 9-a:
The 95% CL upper limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $, obtained using the BDT-based event categorization, as a function of the scalar masses $ m_{\phi_{1}} $ and $ m_{\phi_{2}} $. For the ($ \phi_{1} $, $ \phi_{2} $) mass hypotheses (15, 30), (20, 40), and (30, 60) GeV, only the non-cascade limits are shown. For all other mass hypotheses, either cascade or non-cascade limits are presented, depending on whether the cascade decay is kinematically allowed ($ m_{\phi_{2}} \geq 2 m_{\phi_{1}} $). The numbers displayed in the plot are in \unitpb. |
png pdf |
Figure 9-b:
The 95% CL upper limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $, obtained using the BDT-based event categorization, as a function of the scalar masses $ m_{\phi_{1}} $ and $ m_{\phi_{2}} $. For the ($ \phi_{1} $, $ \phi_{2} $) mass hypotheses (15, 30), (20, 40), and (30, 60) GeV, only the non-cascade limits are shown. For all other mass hypotheses, either cascade or non-cascade limits are presented, depending on whether the cascade decay is kinematically allowed ($ m_{\phi_{2}} \geq 2 m_{\phi_{1}} $). The numbers displayed in the plot are in \unitpb. |
png pdf |
Figure 9-c:
The 95% CL upper limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $, obtained using the BDT-based event categorization, as a function of the scalar masses $ m_{\phi_{1}} $ and $ m_{\phi_{2}} $. For the ($ \phi_{1} $, $ \phi_{2} $) mass hypotheses (15, 30), (20, 40), and (30, 60) GeV, only the non-cascade limits are shown. For all other mass hypotheses, either cascade or non-cascade limits are presented, depending on whether the cascade decay is kinematically allowed ($ m_{\phi_{2}} \geq 2 m_{\phi_{1}} $). The numbers displayed in the plot are in \unitpb. |
png pdf |
Figure 9-d:
The 95% CL upper limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $, obtained using the BDT-based event categorization, as a function of the scalar masses $ m_{\phi_{1}} $ and $ m_{\phi_{2}} $. For the ($ \phi_{1} $, $ \phi_{2} $) mass hypotheses (15, 30), (20, 40), and (30, 60) GeV, only the non-cascade limits are shown. For all other mass hypotheses, either cascade or non-cascade limits are presented, depending on whether the cascade decay is kinematically allowed ($ m_{\phi_{2}} \geq 2 m_{\phi_{1}} $). The numbers displayed in the plot are in \unitpb. |
png pdf |
Figure A1:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A1-a:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A1-b:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A1-c:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mu\tau_\mathrm{h} $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A2:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A2-a:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A2-b:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A2-c:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\tau_\mathrm{h} $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A3:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\mu $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A3-a:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\mu $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A3-b:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\mu $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A3-c:
Background only, post-fit $ m_{\tau\tau} $ distributions for the $ \mathrm{e}\mu $ channel, in events with at least one b-tagged jet: SRL (upper left), SRM (upper right), and SRH (lower). The data are shown by the markers with vertical bars and various backgrounds by the colored histograms. The total systematic uncertainty is shown by the hatched area. The colored open histograms display the predicted signal distribution for two cascade decays and two non-cascade decays, with four different values of $ \phi_{1} $ and $ \phi_{2} $ masses, for an assumed branching fraction of 100%. The lower plot of each panel gives the ratio of the data to the sum of the predicted number of background events. The vertical bars display the statistical uncertainty in the ratio. |
png pdf |
Figure A4:
The observed (points) and median expected (dotted line) 95% CL upper limits on $ \sigma \mathrm{B_{C}} $ for the cascade scenario using the cut-based event categorization and the fit to the $ m_{\tau\tau} $ distribution, for different mass hypotheses ($ m_{\phi_{1}} $, $ m_{\phi_{2}} $). The horizontal bars on the points are for better legibility only. The green and yellow regions show the 68 and 95% expected range for the median value, respectively. |
png pdf |
Figure A5:
The observed (points) and median expected (dotted line) 95% CL upper limits on $ \sigma \mathrm{B_{NC}} $ for the non-cascade scenario using the cut-based event categorization and the fit to the $ m_{\tau\tau} $ distribution, for different mass hypotheses ($ m_{\phi_{1}} $, $ m_{\phi_{2}} $). The horizontal bars on the points are for better legibility only. The green and yellow regions show the 68 and 95% expected range for the median value, respectively. |
png pdf |
Figure A6:
The 95% CL upper limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $ obtained using the cut-based event categorization, as a function of the scalar masses $ m_{\phi_{1}} $ and $ m_{\phi_{2}} $. For the ($ \phi_{1} $, $ \phi_{2} $) mass hypotheses (15, 30), (20, 40), and (30, 60) GeV, only the non-cascade limits are shown. For all other mass hypotheses, either cascade or non-cascade limits are presented, depending on whether the cascade decay is kinematically allowed ($ m_{\phi_{2}} \geq 2 m_{\phi_{1}} $). The numbers displayed in the plot are in \unitpb. |
png pdf |
Figure A6-a:
The 95% CL upper limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $ obtained using the cut-based event categorization, as a function of the scalar masses $ m_{\phi_{1}} $ and $ m_{\phi_{2}} $. For the ($ \phi_{1} $, $ \phi_{2} $) mass hypotheses (15, 30), (20, 40), and (30, 60) GeV, only the non-cascade limits are shown. For all other mass hypotheses, either cascade or non-cascade limits are presented, depending on whether the cascade decay is kinematically allowed ($ m_{\phi_{2}} \geq 2 m_{\phi_{1}} $). The numbers displayed in the plot are in \unitpb. |
png pdf |
Figure A6-b:
The 95% CL upper limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $ obtained using the cut-based event categorization, as a function of the scalar masses $ m_{\phi_{1}} $ and $ m_{\phi_{2}} $. For the ($ \phi_{1} $, $ \phi_{2} $) mass hypotheses (15, 30), (20, 40), and (30, 60) GeV, only the non-cascade limits are shown. For all other mass hypotheses, either cascade or non-cascade limits are presented, depending on whether the cascade decay is kinematically allowed ($ m_{\phi_{2}} \geq 2 m_{\phi_{1}} $). The numbers displayed in the plot are in \unitpb. |
png pdf |
Figure A6-c:
The 95% CL upper limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $ obtained using the cut-based event categorization, as a function of the scalar masses $ m_{\phi_{1}} $ and $ m_{\phi_{2}} $. For the ($ \phi_{1} $, $ \phi_{2} $) mass hypotheses (15, 30), (20, 40), and (30, 60) GeV, only the non-cascade limits are shown. For all other mass hypotheses, either cascade or non-cascade limits are presented, depending on whether the cascade decay is kinematically allowed ($ m_{\phi_{2}} \geq 2 m_{\phi_{1}} $). The numbers displayed in the plot are in \unitpb. |
png pdf |
Figure A6-d:
The 95% CL upper limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $ obtained using the cut-based event categorization, as a function of the scalar masses $ m_{\phi_{1}} $ and $ m_{\phi_{2}} $. For the ($ \phi_{1} $, $ \phi_{2} $) mass hypotheses (15, 30), (20, 40), and (30, 60) GeV, only the non-cascade limits are shown. For all other mass hypotheses, either cascade or non-cascade limits are presented, depending on whether the cascade decay is kinematically allowed ($ m_{\phi_{2}} \geq 2 m_{\phi_{1}} $). The numbers displayed in the plot are in \unitpb. |
| Tables | |
png pdf |
Table 1:
The $ p_{\mathrm{T}} $ thresholds for e, $ \mu $, and $ \tau_\mathrm{h} $ at the trigger level for the three data-taking periods. For the $ \mathrm{e}\tau_\mathrm{h} $ and $ \mu\tau_\mathrm{h} $ channels, the $ p_{\mathrm{T}} $ thresholds for the e and $ \mu $ are dependent on the specific high-level trigger used, i.e.,, the single-lepton or the cross trigger. Thresholds are stated as follows: the single-lepton and cross-trigger $ p_{\mathrm{T}} $ thresholds, and thresholds for the highest $ p_{\mathrm{T}} $ (leading) and second-highest $ p_{\mathrm{T}} $ (subleading) leptons. Multiple single-lepton triggers are listed as comma-separated $ p_{\mathrm{T}} $ thresholds. For cross triggers, the leading and subleading $ p_{\mathrm{T}} $ thresholds are applied simultaneously to the lepton pair. |
png pdf |
Table 2:
List of kinematic variables used as inputs to the BDT discriminator, with their importance rankings. The leading and subleading b-tagged jets are denoted by $ \mathrm{b}_1 $ and $ \mathrm{b}_2 $, respectively. Depending on the channel, the importance of an input variable in the performance of the BDT varies. The increasing importance of a variable in the training is denoted by decreasing numerical values. |
png pdf |
Table 3:
The BDT discriminator score ranges defining the different SRs and CRs. |
png pdf |
Table 4:
Impact of different groups of uncertainties in the observed limits on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $ using BDT-based SR categories. The contribution of each uncertainty group in the total signal strength uncertainty is given as a percentage. Once cascade and one non-cascade example is shown, where the $ \phi_{1} $ and $ \phi_{2} $ mass values are given in GeV. |
png pdf |
Table A1:
Definitions of cut-based event categories in the three channels. The selection boundaries are indicated in GeV. |
| Summary |
| A search for exotic decays of the Higgs boson (H) into a pair of light neutral scalars $ \phi_{1} $ and $ \phi_{2} $ with masses $ m_{\phi_{2}} > m_{\phi_{1}} $, has been presented. Final states with at least one jet coming from the fragmentation of a b quark and two tau leptons are studied. The search utilizes a data sample of proton-proton collisions corresponding to an integrated luminosity of 138 fb$^{-1}$, accumulated by the CMS experiment at the LHC during 2016--2018 at a center-of-mass energy of 13 TeV. The results are dominated by the statistical uncertainties and the systematic uncertainties arising from the normalizations of the backgrounds. Overall, no statistically significant deviation from the expected standard model background prediction is observed, and upper limits are set on the products $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $ for the cascade and non-cascade decay scenarios, respectively, where $ \sigma $ is the Higgs boson production cross section, $ \mathrm{B_{C}}=\mathcal{B}(\mathrm{H} \to \phi_{1} \phi_{2} \to 3 \phi_{1} \to 2\tau4\mathrm{b}) $, and $ \mathrm{B_{NC}} = \mathcal{B}(\mathrm{H} \to \phi_{1} \phi_{2})\ \mathcal{B}(\phi_{1} \to 2\tau)\ \mathcal{B}(\phi_{2} \to 2\mathrm{b}) $. This analysis is sensitive to enhanced branching fractions of the neutral scalars into b quarks and tau leptons for some of the mass hypotheses where $ m_{\phi_{2}} \leq 2m_{\phi_{1}} $. The observed upper limits at 95% confidence level on the combined measurement of $ \sigma \mathrm{B_{C}} $ and $ \sigma \mathrm{B_{NC}} $ range between 0.9 and 36.8\unitpb, depending on the mass hypothesis and decay scenario. These are the first limits using 13 TeV data from CMS on exotic Higgs boson decays into two light neutral scalar particles of unequal masses in final states involving b quarks and tau leptons. |
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