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Search for Higgs bosons decaying into new spin-0 or spin-1 particles in four-lepton final states with the ATLAS detector with 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV

The ATLAS collaboration
CERN-EP-2021-193, 2021.

Abstract (data abstract)
Searches are conducted for new spin-0 or spin-1 bosons using events where a Higgs boson with mass $125$ GeV decays to four leptons ($\ell =$ $e$, $\mu$). This decay is presumed to occur via an intermediate state which contains two on-shell, promptly decaying bosons $H \rightarrow XX/ZX \rightarrow 4\ell$, where the new boson $X$ has a mass between 1 and 60 GeV. The search uses $pp$ collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 139 fb$^{-1}$ at a centre-of-mass energy $\sqrt{s}=13$ TeV. The data are found to be consistent with Standard Model expectations. Limits are set on fiducial cross sections and on the branching ratio of the Higgs boson to decay to $XX/ZX$. Limits are also set on mixing parameters relevant in extensions of the Standard Model containing a dark sector where $X$ is interpreted to be a dark boson.

  • $\langle m_{\ell\ell}\rangle$ distribution in the HM SR

    Data from Figure 3a

    10.17182/hepdata.111057.v1/t1

    Distribution of $\langle m_{\ell\ell}\rangle$ for events selected in the HM $H\to XX \to 4\ell$ $\, ( 15 \,\text{GeV} < m_{X}...

  • $\langle m_{\ell\ell}\rangle$ distribution in the LM SR

    Data from Figure 6a

    10.17182/hepdata.111057.v1/t2

    Distribution of $\langle m_{\ell\ell}\rangle$ for events selected in the LM $H\to XX \to 4\mu$ $( 1 \,\text{GeV} < m_{X} <...

  • $m_{34}$ distribution in the $ZX$ signal region

    Data from Figure 9

    10.17182/hepdata.111057.v1/t3

    Distribution of $m_{34}$ for data and background events in the mass range $115 \,\text{GeV} < m_{4\ell} < 130 \,\text{GeV}$ after...

  • Low and High Mass Efficiencies, $4\mu$ final state

    Model-independent per-channel efficiencies calculated in the fiducial volumes of the Low and High Mass channels for the $4\mu$ final state.

    10.17182/hepdata.111057.v1/t4

    Data from Figure 11a

  • High Mass Efficiency, $2e2\mu$ final state

    Data from Figure 11a

    10.17182/hepdata.111057.v1/t5

    Model-independent per-channel efficiencies calculated in the fiducial volume of the High Mass channel for the $2e2\mu$ final state.

  • High Mass Efficiency, $4e$ final state

    Data from Figure 11a

    10.17182/hepdata.111057.v1/t6

    Model-independent per-channel efficiencies calculated in the fiducial volume of the High Mass channel for the $4e$ final state.

  • Low and High Mass Acceptance, $aa / ss \to 4\mu$

    Data from Figure 11b

    10.17182/hepdata.111057.v1/t7

    Model-dependent per-channel fiducial region acceptances for the $H\to aa\to 4\mu$ process. The regions of 2 GeV to 4.4 GeV, and...

  • High Mass Acceptance, $Z_dZ_d \to 4\mu$

    Data from Figure 11b

    10.17182/hepdata.111057.v1/t8

    Model-dependent per-channel fiducial region acceptances for the $H\to Z_dZ_d\to 4\ell$ process. The regions of 2 GeV to 4.4 GeV, and...

  • High Mass Acceptance, $Z_dZ_d \to 2e2\mu$

    Data from Figure 11b

    10.17182/hepdata.111057.v1/t9

    Model-dependent per-channel fiducial region acceptances for the $H\to Z_dZ_d\to 2e2\mu$ process.

  • High Mass Acceptance, $Z_dZ_d \to 4e$

    Data from Figure 11b

    10.17182/hepdata.111057.v1/t10

    Model-dependent per-channel fiducial region acceptances for the $H\to Z_dZ_d\to 4e$ process.

  • Fiducial $H\to XX \to 4\mu$ limits

    Data from Figure 12a

    10.17182/hepdata.111057.v1/t11

    Upper limits at 95% CL on fiducial cross-sections for the $H\rightarrow XX \rightarrow 4\mu$ process. The step change at $m_X$...

  • Fiducial $H\to XX \to 4e$ limits

    Data from Figure 12b

    10.17182/hepdata.111057.v1/t12

    Upper limits at 95% CL on fiducial cross-sections for the $H\rightarrow XX \rightarrow 4e$ process.

  • Fiducial $H\to XX \to 2e2\mu$ limits

    Data from Figure 12c

    10.17182/hepdata.111057.v1/t13

    Upper limits at 95% CL on fiducial cross-sections for the $H\rightarrow XX \rightarrow 2e2\mu$ process.

  • $gg \to H\to Z_dZ_d\to 4\ell$ limits

    Data from Figure 13

    10.17182/hepdata.111057.v1/t14

    Observed and expected upper limits at 95% CL for the cross section of the $H\to Z_dZ_d\to 4\ell$ process, assuming SM...

  • $gg \to H\to Z_dZ_d\to 4\mu$ limits

    Data from Figure 14a

    10.17182/hepdata.111057.v1/t15

    Observed and expected upper limits at 95% CL for the cross sections of the $H\to Z_dZ_d\to 4\mu$ processes, assuming SM...

  • $gg \to H\to aa \to 4\mu$ limits

    Data from Figure 14b

    10.17182/hepdata.111057.v1/t16

    Observed and expected upper limits at 95% CL for the cross sections of the $H\to aa\to 4\mu$ processes, assuming SM...

  • ZX Efficiency; $4\mu, 2e2\mu$ final states

    Data from Figure 15a

    10.17182/hepdata.111057.v1/t17

    Model-independent efficiencies for the $H\to ZX$ process for the $4\mu$ and $2e2\mu$ final states combined calculated in the $ZX$ fiducial...

  • ZX Efficiency; $4\mu, 2e2\mu, 2\mu2e, 4e$ final states

    Data from Figure 15a

    10.17182/hepdata.111057.v1/t18

    Model-independent efficiencies for the $H\to ZX$ process for the $4\mu$, $2e2\mu$, $2\mu 2e$, and $4e$ final states combined calculated in...

  • ZX Efficiency; $2\mu2e, 4e$ final states

    Data from Figure 15a

    10.17182/hepdata.111057.v1/t19

    Model-independent efficiencies for the $H\to ZX$ process for the $2\mu 2e$, and $4e$ final states combined calculated in the $ZX$...

  • ZX Acceptance; $4\mu, 2e2\mu$ final states

    Data from Figure 15b

    10.17182/hepdata.111057.v1/t20

    Model-dependent per-channel fiducial region acceptances for the $H\to ZZ_d\to 4\ell$ process for the $4\mu$, and $2e2\mu$ final states.

  • ZX Acceptance; $4\mu, 2e2\mu, 2\mu2e, 4e$ final states

    Data from Figure 15b

    10.17182/hepdata.111057.v1/t21

    Model-dependent per-channel fiducial region acceptances for the $H\to ZZ_d\to 4\ell$ process for the $4\mu$, $2e2\mu$, $2\mu 2e$, and $4e$ final...

  • ZX Acceptance; $2\mu2e, 4e$ final states

    Data from Figure 15b

    10.17182/hepdata.111057.v1/t22

    Model-dependent per-channel fiducial region acceptances for the $H\to ZZ_d\to 4\ell$ process for the $2\mu 2e$, and $4e$ final states.

  • Fiducial $H\to ZX \to 2\ell2e$ limits

    Data from Figure 16, $ZX \to 2\ell2e$ channel

    10.17182/hepdata.111057.v1/t23

    Per-channel upper limit at 95% CL on the fiducial cross-section for the $H\rightarrow ZX \to 2\ell2e$ process.

  • Fiducial $H\to ZX \to 2\ell2\mu$ limits

    Data from Figure 16, $ZX \to 2\ell2\mu$ channel

    10.17182/hepdata.111057.v1/t24

    Per-channel upper limit at 95% CL on the fiducial cross-section for the $H\rightarrow ZX \to 2\ell2\mu$ process.

  • $gg \to H\to ZZ_d \to 4\ell$ limits

    Data from Figure 17a

    10.17182/hepdata.111057.v1/t25

    Observed and expected upper limits at 95% CL for the cross sections of the $H\to ZZ_d\to 4\ell$ process, assuming SM...

  • $gg \to H\to Za \to 4\mu$ limits

    Data from Figure 17b

    10.17182/hepdata.111057.v1/t26

    Observed and expected upper limits at 95% CL for the cross sections of the $H\to Za\to 2\ell2\mu$ process, assuming SM...

  • Limits on the $H \to Z_dZ_d$ branching ratio

    Data from Figure 18a

    10.17182/hepdata.111057.v1/t27

    95% CL upper limits on the cross section times the model-dependent branching ratio divided by the SM Higgs boson production...

  • Limits on the $H \to aa$ branching ratio

    Data from Figure 18b

    10.17182/hepdata.111057.v1/t28

    95% CL upper limits on the cross section times the model-dependent branching ratio divided by the SM Higgs boson production...

  • Limits on the effective Higgs mixing parameter

    Data from Figure 19

    10.17182/hepdata.111057.v1/t29

    Upper limit at 95% CL on the effective Higgs mixing parameter $\kappa^\prime=\kappa \, m_H^2 / |m_H^2-m_S^2|$. The regions of 2...

  • Limits on the kinematic mixing parameter

    Data from Figure 20a

    10.17182/hepdata.111057.v1/t30

    Upper limit at 95% CL on the $Z_d$ kinetic mixing parameter $\epsilon$, assuming the SM Higgs boson production cross section.

  • Limits on the mass mixing parameter

    Data from Figure 20b

    10.17182/hepdata.111057.v1/t31

    Upper limit at 95% CL on the $Z$-$Z_d$ mass mixing parameter $\delta^2 \times \textrm{BR}(Z_d\to \ell\ell)$, assuming the SM Higgs boson...

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