CMS-PAS-HIG-17-029 | ||

Search for the exotic decay of the Higgs boson to a pair of light pseudoscalars in the final state of two muons and two $\tau$ leptons at $\sqrt{s}= $ 13 TeV | ||

CMS Collaboration | ||

March 2018 | ||

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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 35.9 fb$^{-1}$ of data accumulated by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV. Masses of the pseudoscalar boson between 15 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.
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Links:
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These preliminary results are superseded in this paper, JHEP 11 (2018) 018.The superseded preliminary plots can be found here. |

Figures | |

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Figure 1:
Parameterized dimuon invariant mass distributions of the $ {\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}} $ (left) and $ {\mathrm {h \to aa \to 4 {\tau}}} $ (right) signal processes simulated at different $ {m_{{\mathrm {a}}}} $ values in the $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ final state. The normalization corresponds to the number of expected signal events after the selection, assuming the production cross section of the Higgs boson predicted in the SM, $\mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}})=0.1%$, and the relation in Eq.(1) to scale the $ {\mathrm {h \to aa \to 4 {\tau}}} $ contribution. |

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Figure 1-a:
Parameterized dimuon invariant mass distributions of the $ {\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}} $ (left) and $ {\mathrm {h \to aa \to 4 {\tau}}} $ (right) signal processes simulated at different $ {m_{{\mathrm {a}}}} $ values in the $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ final state. The normalization corresponds to the number of expected signal events after the selection, assuming the production cross section of the Higgs boson predicted in the SM, $\mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}})=0.1%$, and the relation in Eq.(1) to scale the $ {\mathrm {h \to aa \to 4 {\tau}}} $ contribution. |

png pdf |
Figure 1-b:
Parameterized dimuon invariant mass distributions of the $ {\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}} $ (left) and $ {\mathrm {h \to aa \to 4 {\tau}}} $ (right) signal processes simulated at different $ {m_{{\mathrm {a}}}} $ values in the $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ final state. The normalization corresponds to the number of expected signal events after the selection, assuming the production cross section of the Higgs boson predicted in the SM, $\mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}})=0.1%$, and the relation in Eq.(1) to scale the $ {\mathrm {h \to aa \to 4 {\tau}}} $ contribution. |

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Figure 2:
Parameterization of the reducible (left) and irreducible (right) backgrounds in the $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ final state. The points for the irreducible background represent events selected in simulation, whereas they correspond to observed data events in the same-sign region with relaxed isolation for the reducible background. |

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Figure 2-a:
Parameterization of the reducible (left) and irreducible (right) backgrounds in the $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ final state. The points for the irreducible background represent events selected in simulation, whereas they correspond to observed data events in the same-sign region with relaxed isolation for the reducible background. |

png pdf |
Figure 2-b:
Parameterization of the reducible (left) and irreducible (right) backgrounds in the $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ final state. The points for the irreducible background represent events selected in simulation, whereas they correspond to observed data events in the same-sign region with relaxed isolation for the reducible background. |

png pdf |
Figure 3:
Dimuon mass distributions in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (bottom left), and $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (bottom right) final states. The total background estimation 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 aa \to 2 {\mu} 2 {\tau}}} $ and $ {\mathrm {h \to aa \to 4 {\tau}}} $, and is normalized using $\mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}}) = 0.01%$, 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 distributions in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (bottom left), and $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (bottom right) final states. The total background estimation 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 aa \to 2 {\mu} 2 {\tau}}} $ and $ {\mathrm {h \to aa \to 4 {\tau}}} $, and is normalized using $\mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}}) = 0.01%$, 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 distributions in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (bottom left), and $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (bottom right) final states. The total background estimation 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 aa \to 2 {\mu} 2 {\tau}}} $ and $ {\mathrm {h \to aa \to 4 {\tau}}} $, and is normalized using $\mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}}) = 0.01%$, 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 distributions in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (bottom left), and $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (bottom right) final states. The total background estimation 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 aa \to 2 {\mu} 2 {\tau}}} $ and $ {\mathrm {h \to aa \to 4 {\tau}}} $, and is normalized using $\mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}}) = 0.01%$, 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 distributions in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (bottom left), and $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (bottom right) final states. The total background estimation 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 aa \to 2 {\mu} 2 {\tau}}} $ and $ {\mathrm {h \to aa \to 4 {\tau}}} $, and is normalized using $\mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}}) = 0.01%$, 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 $(\sigma _ {{\mathrm {h}}} /\sigma _{\textrm {SM}})\times \mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}})$, in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (center left), $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (center right) final states, and for the combination of these final states (bottom). The $ {\mathrm {h \to aa \to 4 {\tau}}} $ process is considered as a part of the signal, and is scaled with respect to the $ {\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}} $ signal using Eq.(1). |

png pdf |
Figure 4-a:
Upper limits at 95% CL on $(\sigma _ {{\mathrm {h}}} /\sigma _{\textrm {SM}})\times \mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}})$, in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (center left), $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (center right) final states, and for the combination of these final states (bottom). The $ {\mathrm {h \to aa \to 4 {\tau}}} $ process is considered as a part of the signal, and is scaled with respect to the $ {\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}} $ signal using Eq.(1). |

png pdf |
Figure 4-b:
Upper limits at 95% CL on $(\sigma _ {{\mathrm {h}}} /\sigma _{\textrm {SM}})\times \mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}})$, in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (center left), $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (center right) final states, and for the combination of these final states (bottom). The $ {\mathrm {h \to aa \to 4 {\tau}}} $ process is considered as a part of the signal, and is scaled with respect to the $ {\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}} $ signal using Eq.(1). |

png pdf |
Figure 4-c:
Upper limits at 95% CL on $(\sigma _ {{\mathrm {h}}} /\sigma _{\textrm {SM}})\times \mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}})$, in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (center left), $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (center right) final states, and for the combination of these final states (bottom). The $ {\mathrm {h \to aa \to 4 {\tau}}} $ process is considered as a part of the signal, and is scaled with respect to the $ {\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}} $ signal using Eq.(1). |

png pdf |
Figure 4-d:
Upper limits at 95% CL on $(\sigma _ {{\mathrm {h}}} /\sigma _{\textrm {SM}})\times \mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}})$, in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (center left), $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (center right) final states, and for the combination of these final states (bottom). The $ {\mathrm {h \to aa \to 4 {\tau}}} $ process is considered as a part of the signal, and is scaled with respect to the $ {\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}} $ signal using Eq.(1). |

png pdf |
Figure 4-e:
Upper limits at 95% CL on $(\sigma _ {{\mathrm {h}}} /\sigma _{\textrm {SM}})\times \mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}})$, in the $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\mu}}$ (top left), $ {{\mu}} {{\mu}}+ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), $ {{\mu}} {{\mu}}+ {{\mu}} {{\tau}_{\rm h}} $ (center left), $ {{\mu}} {{\mu}}+ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (center right) final states, and for the combination of these final states (bottom). The $ {\mathrm {h \to aa \to 4 {\tau}}} $ process is considered as a part of the signal, and is scaled with respect to the $ {\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}} $ signal using Eq.(1). |

png pdf |
Figure 5:
Observed limits on $(\sigma _{{{\mathrm {h}}}}/\sigma _{\textrm {SM}})\times \mathcal {B}({{\mathrm {h}}} \to {\mathrm {a}} {\mathrm {a}})$ in 2HDM+S type III (left) and type IV (right). The number 34% corresponds to the limit on the branching fraction of the Higgs boson to BSM particles at the 95% CL obtained with data collected at a center-of-mass energy of 8 TeV by the CMS and ATLAS experiments [10]. |

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Figure 5-a:
Observed limits on $(\sigma _{{{\mathrm {h}}}}/\sigma _{\textrm {SM}})\times \mathcal {B}({{\mathrm {h}}} \to {\mathrm {a}} {\mathrm {a}})$ in 2HDM+S type III (left) and type IV (right). The number 34% corresponds to the limit on the branching fraction of the Higgs boson to BSM particles at the 95% CL obtained with data collected at a center-of-mass energy of 8 TeV by the CMS and ATLAS experiments [10]. |

png pdf |
Figure 5-b:
Observed limits on $(\sigma _{{{\mathrm {h}}}}/\sigma _{\textrm {SM}})\times \mathcal {B}({{\mathrm {h}}} \to {\mathrm {a}} {\mathrm {a}})$ in 2HDM+S type III (left) and type IV (right). The number 34% corresponds to the limit on the branching fraction of the Higgs boson to BSM particles at the 95% CL obtained with data collected at a center-of-mass energy of 8 TeV by the CMS and ATLAS experiments [10]. |

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Figure 6:
Expected and observed 95% CL limits on $\frac {\sigma _h}{\sigma _{\textrm {SM}}}\mathcal {B}(\textrm {h}\rightarrow \textrm {aa})$ in 2HDM+S type III for $\tan\beta =5$. The branching fractions of the pseudoscalar boson to SM particles are computed following a model described in Ref. [13]. Grey shaded regions correspond to regions where theoretical predictions for the branching fractions of the pseudoscalar boson to SM particles are not reliable. The result described in this analysis corresponds to the light blue curves. Results in the $ {\mathrm {b}} {\mathrm {b}} {\tau} {\tau}$ channel were obtained at a center-of-mass energy of 13 TeV [48], while other results were obtained at 8 TeV center-of-mass energy [14]. |

Tables | |

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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. The signal yields are given for $\mathcal {B}({\mathrm {h \to aa \to 2 {\mu} 2 {\tau}}}) = 0.01%$. The $ {\mathrm {h \to aa \to 4 {\tau}}} $ signal is scaled assuming couplings of the pseudoscalar boson proportional to the squared lepton mass, as in Eq.(1). The uncertainties come from statistical and systematic sources. |

Summary |

A search for the 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. The results are extracted from an unbinned fit of the dimuon mass spectrum. Limits are set at the 95% confidence level on the branching fraction $\mathcal{B}({ {\mathrm{h}}} \rightarrow {\mathrm{a}} {\mathrm{a}} \rightarrow 2\mu 2\tau)$ for masses of the light pseudoscalar between 15 and 62.5 GeV, and are as low as $1.2\times 10^{-4}$ for a mass of 60 GeV. These are the most stringent limits obtained in the final state of two muons and two $\tau$ leptons for masses above 15 GeV by more than a factor two, and provide the tightest constraints so far in this mass range on exotic Higgs boson decays in some scenarios where decays of the pseudoscalars to leptons are enhanced. |

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Compact Muon Solenoid LHC, CERN |