CMS-HIG-19-007 ; CERN-EP-2021-093 | ||
Search for low-mass dilepton resonances in Higgs boson decays to four-lepton final states in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
CMS Collaboration | ||
1 November 2021 | ||
Eur. Phys. J. C 82 (2022) 290 | ||
Abstract: A search for low-mass dilepton resonances in Higgs boson decays is conducted in the four-lepton final state. The decay is assumed to proceed via a pair of beyond the standard model particles, or one such particle and a Z boson. The search uses proton-proton collision data collected with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 137 fb$^{-1}$, at a center-of-mass energy $\sqrt{s} = $ 13 TeV. No significant deviation from the standard model expectation is observed. Upper limits at 95% confidence level are set on model-independent Higgs boson decay branching fractions. Additionally, limits on dark photon and axion-like particle production, based on two specific models, are reported. | ||
Links: e-print arXiv:2111.01299 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; |
Figures | |
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Figure 1:
Feynman diagrams for Higgs boson decay via the kinetic-mixing (left) or Higgs-mixing mechanism (right) [7]. The symbol $h$ represents the Higgs boson, and $s$ represents the dark Higgs boson. The symbol ${\varepsilon}$ represents the kinetic-mixing parameter while $\kappa $ represents the Higgs-mixing parameter. |
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Figure 1-a:
Feynman diagram for Higgs boson decay via the kinetic-mixing mechanism [7]. The symbol $h$ represents the Higgs boson. The symbol ${\varepsilon}$ represents the kinetic-mixing parameter. |
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Figure 1-b:
Feynman diagram for Higgs boson decay via the Higgs-mixing mechanism [7]. The symbol $h$ represents the Higgs boson, and $s$ represents the dark Higgs boson. The symbol $\kappa $ represents the Higgs-mixing parameter. |
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Figure 2:
Event yields against $m_{\mathrm{Z} _2}$ with the ZX selection for the muon and electron channels. Numbers in the legend show the total event yields with the ZX selection corresponding to data, and the expected yields for each background and signal processes, along with the corresponding statistical uncertainty coming from the amount of simulated data. |
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Figure 2-a:
Event yields against $m_{\mathrm{Z} _2}$ with the ZX selection for the muon channel. Numbers in the legend show the total event yields with the ZX selection corresponding to data, and the expected yields for each background and signal processes, along with the corresponding statistical uncertainty coming from the amount of simulated data. |
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Figure 2-b:
Event yields against $m_{\mathrm{Z} _2}$ with the ZX selection for the electron channel. Numbers in the legend show the total event yields with the ZX selection corresponding to data, and the expected yields for each background and signal processes, along with the corresponding statistical uncertainty coming from the amount of simulated data. |
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Figure 3:
Event yields against $ {m_{Z12}} = ({m_{{\mathrm{Z} _1}}} + {m_{{\mathrm{Z} _2}}})/2$ with the XX selection for the 4$\mu$, 2e2$\mu$ and 4e final states. Numbers in the legend show the total event yields with the XX selection corresponding to data, and the expected yields for each background and signal processes, along with the corresponding statistical uncertainty coming from the amount of simulated data. |
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Figure 3-a:
Event yields against $ {m_{Z12}} = ({m_{{\mathrm{Z} _1}}} + {m_{{\mathrm{Z} _2}}})/2$ with the XX selection for the 4$\mu$ final state. Numbers in the legend show the total event yields with the XX selection corresponding to data, and the expected yields for each background and signal processes, along with the corresponding statistical uncertainty coming from the amount of simulated data. |
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Figure 3-b:
Event yields against $ {m_{Z12}} = ({m_{{\mathrm{Z} _1}}} + {m_{{\mathrm{Z} _2}}})/2$ with the XX selection for the 2e2$\mu$ final state. Numbers in the legend show the total event yields with the XX selection corresponding to data, and the expected yields for each background and signal processes, along with the corresponding statistical uncertainty coming from the amount of simulated data. |
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Figure 3-c:
Event yields against $ {m_{Z12}} = ({m_{{\mathrm{Z} _1}}} + {m_{{\mathrm{Z} _2}}})/2$ with the XX selection for the 4e final state. Numbers in the legend show the total event yields with the XX selection corresponding to data, and the expected yields for each background and signal processes, along with the corresponding statistical uncertainty coming from the amount of simulated data. |
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Figure 4:
Expected and observed 95% CL limits on $\mathcal {B}(\mathrm{H} \to \mathrm{Z} \mathrm{X}) \mathcal {B}(\mathrm{X} \to \mu \mu)$ assuming X decays to dimuons only, $\mathcal {B}(\mathrm{H} \to \mathrm{Z} \mathrm{X}) \mathcal {B}(\mathrm{X} \to \mathrm{e} \mathrm{e})$ assuming X decays to dielectrons only, and $\mathcal {B}(\mathrm{H} \to \mathrm{Z} \mathrm{X}) \mathcal {B}(\mathrm{X} \to $ ee or $\mu \mu)$ assuming a flavor symmetric decay of X to dimuons and dielectrons. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve is the observed upper limit. The red curve represents the theoretical cross section for the signal process $\mathrm{H} \to \mathrm{Z} \mathrm{X} \to $ 4$\ell $. The discontinuity at 12 GeV in the uncertainty is due to the switch from experimental to theoretical uncertainty estimates of $\mathcal {B}({\mathrm{Z} _{\mathrm {D}}} \to $ ee or $\mu \mu)$, as described in Ref. [7]. The symbol $ {\varepsilon} $ is the kinetic-mixing parameter. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
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Figure 4-a:
Expected and observed 95% CL limits on $\mathcal {B}(\mathrm{H} \to \mathrm{Z} \mathrm{X}) \mathcal {B}(\mathrm{X} \to \mu \mu)$ assuming X decays to dimuons only. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve is the observed upper limit. The discontinuity at 12 GeV in the uncertainty is due to the switch from experimental to theoretical uncertainty estimates of $\mathcal {B}({\mathrm{Z} _{\mathrm {D}}} \to $ ee or $\mu \mu)$, as described in Ref. [7]. The symbol $ {\varepsilon} $ is the kinetic-mixing parameter. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
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Figure 4-b:
Expected and observed 95% CL limits on $\mathcal {B}(\mathrm{H} \to \mathrm{Z} \mathrm{X}) \mathcal {B}(\mathrm{X} \to \mathrm{e} \mathrm{e})$ assuming X decays to dielectrons only. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve is the observed upper limit. The discontinuity at 12 GeV in the uncertainty is due to the switch from experimental to theoretical uncertainty estimates of $\mathcal {B}({\mathrm{Z} _{\mathrm {D}}} \to $ ee or $\mu \mu)$, as described in Ref. [7]. The symbol $ {\varepsilon} $ is the kinetic-mixing parameter. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
png pdf |
Figure 4-c:
Expected and observed 95% CL limits on $\mathcal {B}(\mathrm{H} \to \mathrm{Z} \mathrm{X}) \mathcal {B}(\mathrm{X} \to $ ee or $\mu \mu)$ assuming a flavor symmetric decay of X to dimuons and dielectrons. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve is the observed upper limit. The red curve represents the theoretical cross section for the signal process $\mathrm{H} \to \mathrm{Z} \mathrm{X} \to $ 4$\ell $. The discontinuity at 12 GeV in the uncertainty is due to the switch from experimental to theoretical uncertainty estimates of $\mathcal {B}({\mathrm{Z} _{\mathrm {D}}} \to $ ee or $\mu \mu)$, as described in Ref. [7]. The symbol $ {\varepsilon} $ is the kinetic-mixing parameter. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
png pdf |
Figure 5:
Expected and observed 95% CL limits on $\mathcal {B}(\mathrm{H} \to \mathrm{X} \mathrm{X}) \mathcal {B}(\mathrm{X} \to \mathrm{e} \mathrm{e})^2$ assuming X decays to dielectrons only, $\mathcal {B}(\mathrm{H} \to \mathrm{X} \mathrm{X}) \mathcal {B}(\mathrm{X} \to \mu \mu)^2$ assuming X decays to dimuons only, and $\mathcal {B}(\mathrm{H} \to \mathrm{X} \mathrm{X}) \mathcal {B}(\mathrm{X} \to \mathrm{e} \mathrm{e} \ \text {or}\ mu\mu)^2$ assuming a flavor symmetric decay of X to dimuons and dielectrons. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve is the observed upper limit. The red curve represents the theoretical cross section for the signal process $\mathrm{H} \to \mathrm{X} \mathrm{X} \to $ 4$\ell $. The discontinuity at 12 GeV in uncertainty is due to the switch from experimental to theoretical uncertainty estimates of $\mathcal {B}({\mathrm{Z} _{\mathrm {D}}} \to $ ee or $\mu \mu)$, as described in Ref. [7]. The symbol $\kappa $ is the Higgs-mixing parameter. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
png pdf |
Figure 5-a:
Expected and observed 95% CL limits on $\mathcal {B}(\mathrm{H} \to \mathrm{X} \mathrm{X}) \mathcal {B}(\mathrm{X} \to \mathrm{e} \mathrm{e})^2$ assuming X decays to dielectrons only. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve is the observed upper limit. The discontinuity at 12 GeV in uncertainty is due to the switch from experimental to theoretical uncertainty estimates of $\mathcal {B}({\mathrm{Z} _{\mathrm {D}}} \to $ ee or $\mu \mu)$, as described in Ref. [7]. The symbol $\kappa $ is the Higgs-mixing parameter. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
png pdf |
Figure 5-b:
Expected and observed 95% CL limits on $\mathcal {B}(\mathrm{H} \to \mathrm{X} \mathrm{X}) \mathcal {B}(\mathrm{X} \to \mu \mu)^2$ assuming X decays to dimuons only. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve is the observed upper limit. The discontinuity at 12 GeV in uncertainty is due to the switch from experimental to theoretical uncertainty estimates of $\mathcal {B}({\mathrm{Z} _{\mathrm {D}}} \to $ ee or $\mu \mu)$, as described in Ref. [7]. The symbol $\kappa $ is the Higgs-mixing parameter. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
png pdf |
Figure 5-c:
Expected and observed 95% CL limits on $\mathcal {B}(\mathrm{H} \to \mathrm{X} \mathrm{X}) \mathcal {B}(\mathrm{X} \to \mathrm{e} \mathrm{e} \ \text {or}\ mu\mu)^2$ assuming a flavor symmetric decay of X to dimuons and dielectrons. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve is the observed upper limit. The red curve represents the theoretical cross section for the signal process $\mathrm{H} \to \mathrm{X} \mathrm{X} \to $ 4$\ell $. The discontinuity at 12 GeV in uncertainty is due to the switch from experimental to theoretical uncertainty estimates of $\mathcal {B}({\mathrm{Z} _{\mathrm {D}}} \to $ ee or $\mu \mu)$, as described in Ref. [7]. The symbol $\kappa $ is the Higgs-mixing parameter. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
png pdf |
Figure 6:
95% CL limits on the Higgs-mixing parameter $\kappa $, based on the XX selection, as function of ${m_{{\mathrm{Z} _{\mathrm {D}}}}}$. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve is the observed upper limit. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
png pdf |
Figure 7:
95% CL limit on ${C_{\mathrm{Z} \mathrm{H}}/\Lambda}$ and ${C_{\mathrm{a} \mathrm{H}}/\Lambda ^2}$ as function of $m_{\mathrm{a}}$. Black curves are the expected upper limits, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curves represent the observed upper limits. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
png pdf |
Figure 7-a:
95% CL limit on ${C_{\mathrm{Z} \mathrm{H}}/\Lambda}$ as function of $m_{\mathrm{a}}$. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve represents the observed upper limit. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
png pdf |
Figure 7-b:
95% CL limit on ${C_{\mathrm{a} \mathrm{H}}/\Lambda ^2}$ as function of $m_{\mathrm{a}}$. The dashed black curve is the expected upper limit, with one and two standard-deviation bands shown in green and yellow, respectively. The solid black curve represents the observed upper limit. The grey band corresponds to the excluded region around the $\mathrm{b} \mathrm{\bar{b}} $ bound states of $\Upsilon $. |
Summary |
A search for dilepton resonances in Higgs boson decays to four-lepton final states has been presented. The search considers the two intermediate decay topologies $\mathrm{H} \to \mathrm{Z} \mathrm{X}$ and $\mathrm{H} \to \mathrm{X} \mathrm{X}$. No significant deviations from the standard model expectations are observed. The search imposes experimental constraints on products of model-independent branching fractions of $\mathcal{B}(\mathrm{H} \to \mathrm{Z} \mathrm{X})$, $\mathcal{B}(\mathrm{H} \to \mathrm{X} \mathrm{X})$ and $\mathcal{B}(\mathrm{X} \to \mathrm{e}\mathrm{e}\ \text{or}\ \mu\mu)$, assuming flavor-symmetric decays of X to dimuons and dielectrons, exclusive decays of X to dimuons, and exclusive decays of X to dielectrons, for $m{\mathrm{X}} > $ 4 GeV. In addition, two well-motivated theoretical frameworks beyond the standard model are considered. Due to the presence of the Higgs boson production in LHC proton-proton collisions, the search provides unique constraints on the Higgs-mixing parameter $\kappa < $ 4 $\times$ 10$^{-4}$ at 95% confidence level (CL) in a dark photon model with the XX selection, in Higgs-mixing-dominated scenarios, while searches for ${\mathrm{Z}_{\mathrm{D}}}$ in Drell-Yan processes [67,14] provide better exclusion limits on $\varepsilon$ in kinetic-mixing-dominated scenarios. For the axion-like particle model, upper limits at 95% CL are placed on two relevant Wilson coefficients ${C_{\mathrm{Z}\mathrm{H}}/\Lambda}$ and ${C_{\mathrm{a}\mathrm{H}}/\Lambda^2}$. This is the first direct limit on decays of the observed Higgs boson to axion-like particles decaying to leptons. |
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