CMS-PAS-HIG-22-007

CMS-PAS-HIG-22-007
Search for exotic Higgs boson decays to a pair of pseudoscalars in the $\mu\mu\mathrm{bb}$ and $\tau\tau\mathrm{bb}$ final states in proton-proton collisions with the CMS experiment
CMS Collaboration
23 March 2023

Abstract: A search for the exotic decays of a standard model like Higgs boson (H) with a 125 GeV mass to a pair of light pseudoscalars $\mathrm{a}_1$ is performed in final states where one pseudoscalar decays to two b quarks and the other to two $\tau$ leptons or muons. A data sample of proton-proton collisions at $\sqrt{s}=$ 13 TeV corresponding to an integrated luminosity of 138 fb $^{-1}$ recorded with the CMS detector is exploited. No statistically significant excess is observed over the standard model backgrounds. Upper limits are set, at 95% confidence level (CL), on the Higgs boson branching fraction to $\ell\ell\mathrm{b}\mathrm{b}$ via a pair of $\mathrm{a}_1$ , where $\ell$ stands for muons and tau leptons. The limits depend on the pseudoscalar mass $m_{\mathrm{a}_1}$ . The observed limits are in the range (0.17-3.3) $\times$ 10 $^{-4}$ and (1.7-7.6) $\times$ 10 $^{-2}$ in the $\mu\mu\mathrm{b}\mathrm{b}$ and $\tau\tau\mathrm{b}\mathrm{b}$ final states, respectively. The two final states are combined to obtain exclusion limits of the branching fraction $\mathrm{B}(\mathrm{H}\to\mathrm{a}_1\mathrm{a}_1\to\ell\ell\mathrm{b}\mathrm{b})$ at 95% CL for a broad class of models of a two Higgs doublet extended with a scalar singlet (2HDM+S). Upper bounds on the Higgs boson branching fraction $\mathrm{B}(\mathrm{H}\to\mathrm{a}_1\mathrm{a}_1)$ are also extracted from the combination. $\mathrm{B}(\mathrm{H}\to\mathrm{a}_1\mathrm{a}_1)$ values above 0.23 are excluded at 95% CL for most Type-II 2HDM+S models for $m_{\mathrm{a}_1}$ values between 15 and 60 GeV.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to EPJC. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The distribution of (top) leading and subleading muon $p_{\mathrm{T}}$ and (bottom) leading and subleading jet $p_{\mathrm{T}}$ in selected events. The uncertainty band in the lower panel represents the limited size of simulated samples together with a 30% uncertainty on the low mass Drell-Yan cross section. Simulated samples are normalized to 138 fb $^{-1}$ with the corresponding theoretical cross sections. The benchmark criteria explained in the text are used for signal normalization.
png pdf	Figure 1-a: The distribution of (top) leading and subleading muon $p_{\mathrm{T}}$ and (bottom) leading and subleading jet $p_{\mathrm{T}}$ in selected events. The uncertainty band in the lower panel represents the limited size of simulated samples together with a 30% uncertainty on the low mass Drell-Yan cross section. Simulated samples are normalized to 138 fb $^{-1}$ with the corresponding theoretical cross sections. The benchmark criteria explained in the text are used for signal normalization.
png pdf	Figure 1-b: The distribution of (top) leading and subleading muon $p_{\mathrm{T}}$ and (bottom) leading and subleading jet $p_{\mathrm{T}}$ in selected events. The uncertainty band in the lower panel represents the limited size of simulated samples together with a 30% uncertainty on the low mass Drell-Yan cross section. Simulated samples are normalized to 138 fb $^{-1}$ with the corresponding theoretical cross sections. The benchmark criteria explained in the text are used for signal normalization.
png pdf	Figure 1-c: The distribution of (top) leading and subleading muon $p_{\mathrm{T}}$ and (bottom) leading and subleading jet $p_{\mathrm{T}}$ in selected events. The uncertainty band in the lower panel represents the limited size of simulated samples together with a 30% uncertainty on the low mass Drell-Yan cross section. Simulated samples are normalized to 138 fb $^{-1}$ with the corresponding theoretical cross sections. The benchmark criteria explained in the text are used for signal normalization.
png pdf	Figure 1-d: The distribution of (top) leading and subleading muon $p_{\mathrm{T}}$ and (bottom) leading and subleading jet $p_{\mathrm{T}}$ in selected events. The uncertainty band in the lower panel represents the limited size of simulated samples together with a 30% uncertainty on the low mass Drell-Yan cross section. Simulated samples are normalized to 138 fb $^{-1}$ with the corresponding theoretical cross sections. The benchmark criteria explained in the text are used for signal normalization.
png pdf	Figure 2: The $p_{\mathrm{T}}$ distributions of the (left) dimuon systems, (right) di-b-jets system. The uncertainty band in the lower panel represents the limited size of simulated samples together with a 30% uncertainty on the low mass Drell-Yan cross section. Simulated samples are normalized to 138 fb $^{-1}$ with the corresponding theoretical cross sections. The benchmark criteria explained in the text are used for signal normalization.
png pdf	Figure 2-a: The $p_{\mathrm{T}}$ distributions of the (left) dimuon systems, (right) di-b-jets system. The uncertainty band in the lower panel represents the limited size of simulated samples together with a 30% uncertainty on the low mass Drell-Yan cross section. Simulated samples are normalized to 138 fb $^{-1}$ with the corresponding theoretical cross sections. The benchmark criteria explained in the text are used for signal normalization.
png pdf	Figure 2-b: The $p_{\mathrm{T}}$ distributions of the (left) dimuon systems, (right) di-b-jets system. The uncertainty band in the lower panel represents the limited size of simulated samples together with a 30% uncertainty on the low mass Drell-Yan cross section. Simulated samples are normalized to 138 fb $^{-1}$ with the corresponding theoretical cross sections. The benchmark criteria explained in the text are used for signal normalization.
png pdf	Figure 3: The distribution of $\chi_{\mathrm{b}\mathrm{b}}$ versus $\chi_{\mathrm{H}}$ as defined in Eq. (1) for (left) simulated background processes, and (right) the signal process with $m_{\rm a_1} =$ 40 GeV. The contours encircle the area with $\chi_{\rm tot}$ below an arbitrary value. The grey scale represents the expected yields at 138 fb $^{-1}$ .
png pdf	Figure 3-a: The distribution of $\chi_{\mathrm{b}\mathrm{b}}$ versus $\chi_{\mathrm{H}}$ as defined in Eq. (1) for (left) simulated background processes, and (right) the signal process with $m_{\rm a_1} =$ 40 GeV. The contours encircle the area with $\chi_{\rm tot}$ below an arbitrary value. The grey scale represents the expected yields at 138 fb $^{-1}$ .
png pdf	Figure 3-b: The distribution of $\chi_{\mathrm{b}\mathrm{b}}$ versus $\chi_{\mathrm{H}}$ as defined in Eq. (1) for (left) simulated background processes, and (right) the signal process with $m_{\rm a_1} =$ 40 GeV. The contours encircle the area with $\chi_{\rm tot}$ below an arbitrary value. The grey scale represents the expected yields at 138 fb $^{-1}$ .
png pdf	Figure 4: Signal ( $m_{\rm a_1}=$ 40 GeV) versus background efficiency for different thresholds on $\chi_{\rm tot}^2$ (gray) and $\chi_{\rm d}^2$ (red) variables. The black star indicates signal efficiency versus that of background for the optimized $\chi_{\rm d}^2$ requirement.
png pdf	Figure 5: Pre-fit distributions of the transformed DNN score for the $\mu\,\tau_\mathrm{h}$ \ channel divided into events with one (left) or at least two (right) b jets. The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 100%. The lower panel shows the ratio of the observed data to the expected yields. The grey band represents the constrained statistical and systematic uncertainties.
png pdf	Figure 5-a: Pre-fit distributions of the transformed DNN score for the $\mu\,\tau_\mathrm{h}$ \ channel divided into events with one (left) or at least two (right) b jets. The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 100%. The lower panel shows the ratio of the observed data to the expected yields. The grey band represents the constrained statistical and systematic uncertainties.
png pdf	Figure 5-b: Pre-fit distributions of the transformed DNN score for the $\mu\,\tau_\mathrm{h}$ \ channel divided into events with one (left) or at least two (right) b jets. The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 100%. The lower panel shows the ratio of the observed data to the expected yields. The grey band represents the constrained statistical and systematic uncertainties.
png pdf	Figure 6: The best-fit background models together with 68% CL uncertainty band from the fit to the data under the background-only hypothesis for the (top left) TT category, (top right) TM, (middle left) TL category, (middle right) Low $p_{\mathrm{T}}$ category, and (bottom) VBF category.
png pdf	Figure 6-a: The best-fit background models together with 68% CL uncertainty band from the fit to the data under the background-only hypothesis for the (top left) TT category, (top right) TM, (middle left) TL category, (middle right) Low $p_{\mathrm{T}}$ category, and (bottom) VBF category.
png pdf	Figure 6-b: The best-fit background models together with 68% CL uncertainty band from the fit to the data under the background-only hypothesis for the (top left) TT category, (top right) TM, (middle left) TL category, (middle right) Low $p_{\mathrm{T}}$ category, and (bottom) VBF category.
png pdf	Figure 6-c: The best-fit background models together with 68% CL uncertainty band from the fit to the data under the background-only hypothesis for the (top left) TT category, (top right) TM, (middle left) TL category, (middle right) Low $p_{\mathrm{T}}$ category, and (bottom) VBF category.
png pdf	Figure 6-d: The best-fit background models together with 68% CL uncertainty band from the fit to the data under the background-only hypothesis for the (top left) TT category, (top right) TM, (middle left) TL category, (middle right) Low $p_{\mathrm{T}}$ category, and (bottom) VBF category.
png pdf	Figure 6-e: The best-fit background models together with 68% CL uncertainty band from the fit to the data under the background-only hypothesis for the (top left) TT category, (top right) TM, (middle left) TL category, (middle right) Low $p_{\mathrm{T}}$ category, and (bottom) VBF category.
png pdf	Figure 7: Post-fit distributions of the $m_{\tau\tau}$ for the $\mu\,\tau_\mathrm{h}$ \ channel signal regions in events with exactly one b-tagged jet: SR1 (top left), SR2 (top right), and SR3 (bottom). The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 10%.
png pdf	Figure 7-a: Post-fit distributions of the $m_{\tau\tau}$ for the $\mu\,\tau_\mathrm{h}$ \ channel signal regions in events with exactly one b-tagged jet: SR1 (top left), SR2 (top right), and SR3 (bottom). The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 10%.
png pdf	Figure 7-b: Post-fit distributions of the $m_{\tau\tau}$ for the $\mu\,\tau_\mathrm{h}$ \ channel signal regions in events with exactly one b-tagged jet: SR1 (top left), SR2 (top right), and SR3 (bottom). The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 10%.
png pdf	Figure 7-c: Post-fit distributions of the $m_{\tau\tau}$ for the $\mu\,\tau_\mathrm{h}$ \ channel signal regions in events with exactly one b-tagged jet: SR1 (top left), SR2 (top right), and SR3 (bottom). The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 10%.
png pdf	Figure 8: Post-fit distributions of the $m_{\tau\tau}$ for the $\mu\,\tau_\mathrm{h}$ \ channel signal regions in events with at least two b-tagged jets: SR1 (left) and SR2 (right). The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 10%.
png pdf	Figure 8-a: Post-fit distributions of the $m_{\tau\tau}$ for the $\mu\,\tau_\mathrm{h}$ \ channel signal regions in events with at least two b-tagged jets: SR1 (left) and SR2 (right). The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 10%.
png pdf	Figure 8-b: Post-fit distributions of the $m_{\tau\tau}$ for the $\mu\,\tau_\mathrm{h}$ \ channel signal regions in events with at least two b-tagged jets: SR1 (left) and SR2 (right). The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 10%.
png pdf	Figure 9: Post-fit distributions of the $m_{\tau\tau}$ for the $\mu\,\tau_\mathrm{h}$ \ channel control regions in events with exactly one b-tagged jet (left) and at least two b-tagged jets (right). The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 10%.
png pdf	Figure 9-a: Post-fit distributions of the $m_{\tau\tau}$ for the $\mu\,\tau_\mathrm{h}$ \ channel control regions in events with exactly one b-tagged jet (left) and at least two b-tagged jets (right). The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 10%.
png pdf	Figure 9-b: Post-fit distributions of the $m_{\tau\tau}$ for the $\mu\,\tau_\mathrm{h}$ \ channel control regions in events with exactly one b-tagged jet (left) and at least two b-tagged jets (right). The shape of the $\mathrm{H}\to{\rm a_1}{\rm a_1}$ signal, where $m_{\rm a_1} =$ 35 GeV, is indicated assuming $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ to be 10%.
png pdf	Figure 10: Observed and expected upper limits at 95% CL on $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to \mu\mu{\mathrm{b}}{\mathrm{b}})$ as a function of $m_{\rm a_1}$ . The inner and outer bands indicate the regions containing the distribution of limits located within 68 and 95% confidence intervals, respectively, of the expectation under the background-only hypothesis.
png pdf	Figure 11: Observed and expected 95% CL exclusion limits on $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ in %, for the combination of all years with an integrated luminosity of 138 fb $^{-1}$ per channel and the combination. Top left: $\mu\,\tau_\mathrm{h}$ , top right: $\mathrm{e}\,\tau_\mathrm{h}$ , bottom left: $\mathrm{e}\,\mu$ , and bottom right: combination of all channels is shown.
png pdf	Figure 11-a: Observed and expected 95% CL exclusion limits on $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ in %, for the combination of all years with an integrated luminosity of 138 fb $^{-1}$ per channel and the combination. Top left: $\mu\,\tau_\mathrm{h}$ , top right: $\mathrm{e}\,\tau_\mathrm{h}$ , bottom left: $\mathrm{e}\,\mu$ , and bottom right: combination of all channels is shown.
png pdf	Figure 11-b: Observed and expected 95% CL exclusion limits on $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ in %, for the combination of all years with an integrated luminosity of 138 fb $^{-1}$ per channel and the combination. Top left: $\mu\,\tau_\mathrm{h}$ , top right: $\mathrm{e}\,\tau_\mathrm{h}$ , bottom left: $\mathrm{e}\,\mu$ , and bottom right: combination of all channels is shown.
png pdf	Figure 11-c: Observed and expected 95% CL exclusion limits on $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ in %, for the combination of all years with an integrated luminosity of 138 fb $^{-1}$ per channel and the combination. Top left: $\mu\,\tau_\mathrm{h}$ , top right: $\mathrm{e}\,\tau_\mathrm{h}$ , bottom left: $\mathrm{e}\,\mu$ , and bottom right: combination of all channels is shown.
png pdf	Figure 11-d: Observed and expected 95% CL exclusion limits on $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ in %, for the combination of all years with an integrated luminosity of 138 fb $^{-1}$ per channel and the combination. Top left: $\mu\,\tau_\mathrm{h}$ , top right: $\mathrm{e}\,\tau_\mathrm{h}$ , bottom left: $\mathrm{e}\,\mu$ , and bottom right: combination of all channels is shown.
png pdf	Figure 12: Observed and expected 95% CL upper limits on $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\ell\ell\mathrm{b}\mathrm{b})$ in %, where $\ell$ stands for muons or tau leptons, obtained from the combination of $\mu\mu{\mathrm{b}}{\mathrm{b}}$ and $\tau\tau{\mathrm{b}}{\mathrm{b}}$ channels using the full Run 2 integrated luminosity of 138 fb $^{-1}$ . The results are obtained as functions of $m_{\rm a_1}$ for 2HDM+S models, independent of the type and $\tan\beta$ parameter.
png pdf	Figure 13: Observed 95% CL upper limits on $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1})$ in %, for the combination of $\mu\mu{\mathrm{b}}{\mathrm{b}}$ and $\tau\tau{\mathrm{b}}{\mathrm{b}}$ channels using the full Run 2 integrated luminosity of 138 fb $^{-1}$ for Type III (left) and Type IV (right) 2HDM+S in the $\tan\beta$ vs. $m_{\rm a_1}$ phase space. The contours corresponding to branching fractions of 100% and 16% are drawn using dashed lines where 16% refers to the combined upper limit on Higgs to BSM particle decays from previous Run 2 results [10]. Linear extrapolation has been used between different points on the figures.
png pdf	Figure 13-a: Observed 95% CL upper limits on $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1})$ in %, for the combination of $\mu\mu{\mathrm{b}}{\mathrm{b}}$ and $\tau\tau{\mathrm{b}}{\mathrm{b}}$ channels using the full Run 2 integrated luminosity of 138 fb $^{-1}$ for Type III (left) and Type IV (right) 2HDM+S in the $\tan\beta$ vs. $m_{\rm a_1}$ phase space. The contours corresponding to branching fractions of 100% and 16% are drawn using dashed lines where 16% refers to the combined upper limit on Higgs to BSM particle decays from previous Run 2 results [10]. Linear extrapolation has been used between different points on the figures.
png pdf	Figure 13-b: Observed 95% CL upper limits on $\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1})$ in %, for the combination of $\mu\mu{\mathrm{b}}{\mathrm{b}}$ and $\tau\tau{\mathrm{b}}{\mathrm{b}}$ channels using the full Run 2 integrated luminosity of 138 fb $^{-1}$ for Type III (left) and Type IV (right) 2HDM+S in the $\tan\beta$ vs. $m_{\rm a_1}$ phase space. The contours corresponding to branching fractions of 100% and 16% are drawn using dashed lines where 16% refers to the combined upper limit on Higgs to BSM particle decays from previous Run 2 results [10]. Linear extrapolation has been used between different points on the figures.

Tables
png pdf	Table 1: The electron, muon, and $\tau_\mathrm{h} p_{\mathrm{T}}$ thresholds in GeV at trigger level for the $\tau\tau{\mathrm{b}}{\mathrm{b}}$ and $\mu\mu{\mathrm{b}}{\mathrm{b}}$ final states.
png pdf	Table 2: Event yields for simulated processes and the number of observed events in data after applying $\chi_{\rm d}^2 <$ 1.5. The expected number of simulated events is normalized to the integrated luminosity of 138 fb $^{-1}$ . The type-III parametrization of 2HDM+S with $\tan\beta=$ 2 is used to evaluate Br( ${\rm a_1}\to ff$ ).
png pdf	Table 3: Summary of categorization requirements. Events in these categories contain two muons and two b-jets. As stated in the text, L, M, and T respectively stand for the loose, medium, and tight b-tag criteria.
png pdf	Table 4: The expected yields for backgrounds and different signal hypotheses in each category. The entries are rounded to first decimal place.
png pdf	Table 5: Event categories and subregions for the $\tau\tau{\mathrm{b}}{\mathrm{b}}$ channel. The values correspond to the transformed DNN score used to define the signal (SRn) and control (CR) regions.

Summary

A search for an exotic decay of the 125 GeV Higgs boson to a pair of light pseudoscalar bosons in the final state with two b quarks and two

$\tau$ leptons or muons has been presented. The results are based on a data sample of proton-proton collisions corresponding to an integrated luminosity of 138 fb

$^{-1}$ , accumulated by the CMS experiment during LHC Run 2 at a center-of-mass energy of 13 TeV. Final states with at least one leptonic

$\tau$ decay are studied in

$\tau\tau{\mathrm{b}}{\mathrm{b}}$ , excluding those with two muons or two electrons. The results show significant improvement with respect to the earlier CMS analyses at 13\, TeV, beyond what is merely expected from the increase in the size of the data sample. The new

$\tau\tau{\mathrm{b}}{\mathrm{b}}$ analysis gains from the deep neural network based signal categorization, while a more thorough analysis of the signal properties using a single discrimination variable improves

$\mu\mu{\mathrm{b}}{\mathrm{b}}$ . In the absence of any significant excess in the data over the standard model backgrounds, upper limits are set, at 95% confidence level on

$\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\mu\mu{\mathrm{b}}{\mathrm{b}})$ and

$\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1}\to\tau\tau{\mathrm{b}}{\mathrm{b}})$ , in the

$\mu\mu{\mathrm{b}}{\mathrm{b}}$ and

$\tau\tau{\mathrm{b}}{\mathrm{b}}$ analyses respectively. Both analyses provide the most stringent expected limits to date. In

$\mu\mu{\mathrm{b}}{\mathrm{b}}$ , the observed limits are in the range (0.35-2.6)

$\times$ 10

$^{-4}$ for a pseudoscalar mass,

$m_{\rm a_1}$ , between 15 and 62.5 GeV. Combining all final states in

$\tau\tau{\mathrm{b}}{\mathrm{b}}$ , limits are observed to be in range (1.8--7.7)% for

$m_{\rm a_1}$ between 12 and 60 GeV. In the context of 2HDM+S models, the allowed values of the branching fraction

$\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1})$ are obtained by combining the

$\mu\mu{\mathrm{b}}{\mathrm{b}}$ and

$\tau\tau{\mathrm{b}}{\mathrm{b}}$ channels. For

$m_{\rm a_1}$ values between 15 and 60 GeV,

$\mathrm{B}(\mathrm{H}\to{\rm a_1}{\rm a_1})$ above 23% are excluded, at 95% confidence level, in most of the Type-II models. In Type III and IV, upper limits as low as about 2% and 3% are obtained, respectively, for

$\tan\beta=$ 2.0 and 0.5.

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