CMS-HIG-17-029

CMS-HIG-17-029 ; CERN-EP-2018-078
Search for an exotic decay of the Higgs boson to a pair of light pseudoscalars in the final state of two muons and two $\tau$ leptons in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
13 May 2018
JHEP 11 (2018) 018
Abstract: A search for exotic Higgs boson decays to light pseudoscalars in the final state of two muons and two $\tau$ leptons is performed using proton-proton collision data recorded by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV in 2016, corresponding to an integrated luminosity of 35.9 fb $^{-1}$ . Masses of the pseudoscalar boson between 15.0 and 62.5 GeV are probed, and no significant excess of data is observed above the prediction of the standard model. Upper limits are set on the branching fraction of the Higgs boson to two light pseudoscalar bosons in different types of two-Higgs-doublet models extended with a complex scalar singlet.
Links: e-print arXiv:1805.04865 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Parameterized dimuon invariant mass distributions of the $\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}$ (left) and ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ (right) signal processes simulated at different ${m_{\mathrm{a}}}$ values in the ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ final state. The normalization corresponds to the number of expected signal events after the selection for an integrated luminosity of 35.9 fb $^{-1}$ , assuming the production cross section of the Higgs boson predicted in the SM, $\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}})=0.1%$ , and the relation in Eq. (1) to scale the ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ contribution.
png pdf	Figure 1-a: Parameterized dimuon invariant mass distribution of the $\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}$ signal process simulated at different ${m_{\mathrm{a}}}$ values in the ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ final state. The normalization corresponds to the number of expected signal events after the selection for an integrated luminosity of 35.9 fb $^{-1}$ , assuming the production cross section of the Higgs boson predicted in the SM, $\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}})=0.1%$ .
png pdf	Figure 1-b: Parameterized dimuon invariant mass distribution of the ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ signal process simulated at different ${m_{\mathrm{a}}}$ values in the ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ final state. The normalization corresponds to the number of expected signal events after the selection for an integrated luminosity of 35.9 fb $^{-1}$ , assuming the production cross section of the Higgs boson predicted in the SM, $\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}})=0.1%$ , and the relation in Eq. (1) to scale the ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ contribution.
png pdf	Figure 2: Parameterization of the shape of the background with misidentified ${\tau}$ leptons (left) and ${{m_{\mathrm{Z}}}}$ pair production background (right) in the ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ final state. The points for the ${{m_{\mathrm{Z}}}} {{m_{\mathrm{Z}}}}$ background represent events selected in simulation, whereas they correspond to observed data events in the SS region with relaxed isolation for the background with misidentified ${\tau}$ leptons.
png pdf	Figure 2-a: Parameterization of the shape of the background with misidentified ${\tau}$ leptons in the ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ final state. The points correspond to observed data events in the SS region with relaxed isolation.
png pdf	Figure 2-b: Parameterization of the shape of the background with ${{m_{\mathrm{Z}}}}$ pair production background in the ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ final state. The points represent events selected in simulation.
png pdf	Figure 3: Dimuon mass distributions in the ${{\mu}} {{\mu}}+ {\mathrm{e}} {{\mu}}$ (upper left), ${{\mu}} {{\mu}}+ {\mathrm{e}} {{\tau} _{\mathrm{h}}}$ (upper right), ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ (lower left), and ${{\mu}} {{\mu}}+ {{\tau} _{\mathrm{h}}} {{\tau} _{\mathrm{h}}}$ (lower right) final states. The total background estimate and its uncertainty are given by the black lines. The histograms for the two background components are shown for illustrative purposes only as the background models are extracted from unbinned fits. The signal model is drawn in blue above the background model: it includes both ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ and ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ , and is normalized using $\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}) =$ 0.01%, assuming the relation in Eq. (1) to determine the relative proportion of these processes. The production cross section of the Higgs boson predicted in the SM is assumed.
png pdf	Figure 3-a: Dimuon mass distribution in the ${{\mu}} {{\mu}}+ {\mathrm{e}} {{\mu}}$ final state. The total background estimate and its uncertainty are given by the black lines. The histograms for the two background components are shown for illustrative purposes only as the background models are extracted from unbinned fits. The signal model is drawn in blue above the background model: it includes both ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ and ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ , and is normalized using $\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}) =$ 0.01%, assuming the relation in Eq. (1) to determine the relative proportion of these processes. The production cross section of the Higgs boson predicted in the SM is assumed.
png pdf	Figure 3-b: Dimuon mass distribution in the ${{\mu}} {{\mu}}+ {\mathrm{e}} {{\tau} _{\mathrm{h}}}$ final state. The total background estimate and its uncertainty are given by the black lines. The histograms for the two background components are shown for illustrative purposes only as the background models are extracted from unbinned fits. The signal model is drawn in blue above the background model: it includes both ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ and ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ , and is normalized using $\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}) =$ 0.01%, assuming the relation in Eq. (1) to determine the relative proportion of these processes. The production cross section of the Higgs boson predicted in the SM is assumed.
png pdf	Figure 3-c: Dimuon mass distribution in the ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ final state. The total background estimate and its uncertainty are given by the black lines. The histograms for the two background components are shown for illustrative purposes only as the background models are extracted from unbinned fits. The signal model is drawn in blue above the background model: it includes both ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ and ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ , and is normalized using $\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}) =$ 0.01%, assuming the relation in Eq. (1) to determine the relative proportion of these processes. The production cross section of the Higgs boson predicted in the SM is assumed.
png pdf	Figure 3-d: Dimuon mass distribution in the ${{\mu}} {{\mu}}+ {{\tau} _{\mathrm{h}}} {{\tau} _{\mathrm{h}}}$ final state. The total background estimate and its uncertainty are given by the black lines. The histograms for the two background components are shown for illustrative purposes only as the background models are extracted from unbinned fits. The signal model is drawn in blue above the background model: it includes both ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ and ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ , and is normalized using $\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}) =$ 0.01%, assuming the relation in Eq. (1) to determine the relative proportion of these processes. The production cross section of the Higgs boson predicted in the SM is assumed.
png pdf	Figure 4: Upper limits at 95% CL on $(\sigma _ {{\mathrm{h}}} /\sigma _{\textrm {SM}})\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}})$ , in the ${{\mu}} {{\mu}}+ {\mathrm{e}} {{\mu}}$ (upper left), ${{\mu}} {{\mu}}+ {\mathrm{e}} {{\tau} _{\mathrm{h}}}$ (upper right), ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ (middle left), ${{\mu}} {{\mu}}+ {{\tau} _{\mathrm{h}}} {{\tau} _{\mathrm{h}}}$ (middle right) final states, and for the combination of these final states (lower). The ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ process is considered as a part of the signal, and is scaled with respect to the ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ signal using Eq. (1).
png pdf	Figure 4-a: Upper limits at 95% CL on $(\sigma _ {{\mathrm{h}}} /\sigma _{\textrm {SM}})\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}})$ , in the ${{\mu}} {{\mu}}+ {\mathrm{e}} {{\mu}}$ final state. The ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ process is considered as a part of the signal, and is scaled with respect to the ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ signal using Eq. (1).
png pdf	Figure 4-b: Upper limits at 95% CL on $(\sigma _ {{\mathrm{h}}} /\sigma _{\textrm {SM}})\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}})$ , in the ${{\mu}} {{\mu}}+ {\mathrm{e}} {{\tau} _{\mathrm{h}}}$ final state. The ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ process is considered as a part of the signal, and is scaled with respect to the ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ signal using Eq. (1).
png pdf	Figure 4-c: Upper limits at 95% CL on $(\sigma _ {{\mathrm{h}}} /\sigma _{\textrm {SM}})\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}})$ , in the ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ final state. The ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ process is considered as a part of the signal, and is scaled with respect to the ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ signal using Eq. (1).
png pdf	Figure 4-d: Upper limits at 95% CL on $(\sigma _ {{\mathrm{h}}} /\sigma _{\textrm {SM}})\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}})$ , in the ${{\mu}} {{\mu}}+ {{\tau} _{\mathrm{h}}} {{\tau} _{\mathrm{h}}}$ final state. The ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ process is considered as a part of the signal, and is scaled with respect to the ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ signal using Eq. (1).
png pdf	Figure 4-e: Upper limits at 95% CL on $(\sigma _ {{\mathrm{h}}} /\sigma _{\textrm {SM}})\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}})$ , for the combination of ${{\mu}} {{\mu}}+ {\mathrm{e}} {{\mu}}$ , ${{\mu}} {{\mu}}+ {\mathrm{e}} {{\tau} _{\mathrm{h}}}$ , ${{\mu}} {{\mu}}+ {{\mu}} {{\tau} _{\mathrm{h}}}$ , and ${{\mu}} {{\mu}}+ {{\tau} _{\mathrm{h}}} {{\tau} _{\mathrm{h}}}$ final states. The ${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ process is considered as a part of the signal, and is scaled with respect to the ${\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}$ signal using Eq. (1).
png pdf	Figure 5: Observed limits on $(\sigma _{{{\mathrm{h}}}}/\sigma _{ \mathrm{SM}})\mathcal{B}({{\mathrm{h}}} \to \mathrm{aa})$ in 2HDM+S type III (left) and type IV (right). The contour lines shown for $\mathcal{B}({{\mathrm{h}}} \to \mathrm{aa})=$ 1.0 and 0.34 correspond to the colour scale indicated on the right vertical scale. The number 0.34 corresponds to the limit on the branching fraction of the Higgs boson to beyond-the-SM particles at 95% CL obtained with data collected at center-of-mass energies of 7 and 8 TeV by the CMS and ATLAS experiments [10].
png pdf	Figure 5-a: Observed limits on $(\sigma _{{{\mathrm{h}}}}/\sigma _{ \mathrm{SM}})\mathcal{B}({{\mathrm{h}}} \to \mathrm{aa})$ in 2HDM+S type III. The contour lines shown for $\mathcal{B}({{\mathrm{h}}} \to \mathrm{aa})=$ 1.0 and 0.34 correspond to the colour scale indicated on the right vertical scale. The number 0.34 corresponds to the limit on the branching fraction of the Higgs boson to beyond-the-SM particles at 95% CL obtained with data collected at center-of-mass energies of 7 and 8 TeV by the CMS and ATLAS experiments [10].
png pdf	Figure 5-b: Observed limits on $(\sigma _{{{\mathrm{h}}}}/\sigma _{ \mathrm{SM}})\mathcal{B}({{\mathrm{h}}} \to \mathrm{aa})$ in 2HDM+S type IV. The contour lines shown for $\mathcal{B}({{\mathrm{h}}} \to \mathrm{aa})=$ 1.0 and 0.34 correspond to the colour scale indicated on the right vertical scale. The number 0.34 corresponds to the limit on the branching fraction of the Higgs boson to beyond-the-SM particles at 95% CL obtained with data collected at center-of-mass energies of 7 and 8 TeV by the CMS and ATLAS experiments [10].

Tables

png pdf

Table 1:
Yields of the signal and background processes in the four final states, as well as the number of observed events in each final state, in the dimuon mass range between 14 and 64 GeV. The signal yields are given for

$\mathcal{B}({\mathrm{h} \to \mathrm{aa}\to 2 {\mu} 2{{\tau}}}) =$ 0.01%. The

${\mathrm{h} \to \mathrm{aa}\to 4{{\tau}}}$ signal is scaled assuming the couplings of the pseudoscalar boson proportional to the squared lepton mass, as in Eq. (1). The production cross section of the Higgs boson predicted in the SM is assumed. The uncertainties combine the statistical and systematic sources.

Summary

A search for an exotic decay of the Higgs boson to a pair of light pseudoscalars in the final state of two muons and two

$\tau$ leptons has been performed using data collected by the CMS experiment in 2016 at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 35.9 fb

$^{-1}$ . The results are extracted from an unbinned fit of the dimuon mass spectrum. Limits are set at 95% confidence level on the branching fraction

$\mathcal{B}(\mathcal{h}\to\mathrm{a}\mathrm{a}\to2\mu2\tau)$ for the masses of the light pseudoscalar between 15.0 and 62.5 GeV, and are as low as

$1.2\times 10^{-4}$ for a mass of 60 GeV assuming the SM production cross section for the Higgs boson. These are the most stringent limits obtained in the final state of two muons and two

$\tau$ leptons for the masses above 15 GeV, improving previous limits [14,20] by more than a factor two. They provide the tightest constraints in this mass range on exotic Higgs boson decays in scenarios where the decays of pseudoscalar bosons to leptons are enhanced.

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