Search for light long-lived neutral particles from Higgs boson decays via vector-boson-fusion production from $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

The ATLAS collaboration
Eur.Phys.J.C 84 (2024) 719, 2024.

Abstract (data abstract)
A search is reported for long-lived dark photons with masses between 0.1 and 15 GeV, from exotic decays of Higgs bosons produced via vector-boson-fusion. Events that contain displaced collimated Standard Model fermions reconstructed in the calorimeter or muon spectrometer are probed to search for long-lived dark photon candidates that then decay into collimated jets of leptons or light hadrons. This search uses the full LHC Run 2 (2015-2018) data sample collected in proton-proton collisions at $\sqrt{s}$=13 TeV, corresponding to an integrated luminosity of 139 fb$^{-1}$. Dominant backgrounds from Standard Model processes and non-collision sources are estimated by using data-driven techniques. The observed event yields in the signal regions are consistent with the expected background. Upper limits on the Higgs boson to dark photon branching fraction are reported as a function of the mean dark photon proper decay length, or as a function of the dark-photon mass and kinetic mixing parameter that quantifies the coupling between the Standard Model and potential dark sector. These limits are also combined with previous ATLAS results obtained in the gluon-gluon fusion and WH production modes. A branching fraction above 10% is excluded at 95% CL for a Higgs boson decaying into two dark photons for dark-photon mean proper decay lengths between 173 and 1296 mm and mass of 10 GeV.

  • Figure 5a

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    Observed 95% CL upper limits on B(H→ 2γd+X) for different γd masses and a 125 GeV Higgs boson, as a function of...

  • Figure 5b

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    Observed 95% CL upper limits on B(H→ 2γd+X) for different γd masses and a 125 GeV Higgs boson, as a function of...

  • Figure 5c

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    Observed 95% CL upper limits on B(H→ 2γd+X) for different γd masses and a 125 GeV Higgs boson, as a function of...

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    Observed 95% CL upper limits on B(H→ 2γd+X) for different γd masses and a 125 GeV Higgs boson, as a function of...

  • Figure 6a

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    Observed 95% CL upper limits on B(H→ 2γd+X) for a γd mass of 100 MeV, as a function of the dark-photon mean...

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    Observed 95% CL upper limits on B(H→ 2γd+X) for a γd mass of 10 GeV, as a function of the dark-photon mean...

  • Auxiliary figure 3a

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    Acceptance times efficiency extrapolated as a function of cτγd for the μDPJ channel (SRμ), obtained for the different FRVZ MC...

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    Acceptance times efficiency extrapolated as a function of cτγd for the low ETmiss caloDPJ channel (SRcL), obtained for the different...

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    Acceptance times efficiency extrapolated as a function of cτγd for the high ETmiss caloDPJ channel (SRcH), obtained for the different...

  • Auxiliary figure 4a

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    Observed (solid line) and expected (dashed line) 95% CL upper limits on B(H→ 2γd+X) for FRVZ processes with a 125 GeV Higgs...

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    Observed (solid line) and expected (dashed line) 95% CL upper limits on B(H→ 2γd+X) for FRVZ processes with a 125 GeV Higgs...

  • Auxiliary figure 4c

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    Observed (solid line) and expected (dashed line) 95% CL upper limits on B(H→ 2γd+X) for FRVZ processes with a 125 GeV Higgs...

  • Auxiliary figure 4d

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    Observed (solid line) and expected (dashed line) 95% CL upper limits on B(H→ 2γd+X) for FRVZ processes with a 125 GeV Higgs...

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    Observed (solid line) and expected (dashed line) 95% CL upper limits on B(H→ 2γd+X) for FRVZ processes with a 125 GeV Higgs...

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    Observed (solid line) and expected (dashed line) 95% CL upper limits on B(H→ 2γd+X) for FRVZ processes with a 125 GeV Higgs...

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    Observed (solid line) and expected (dashed line) 95% CL upper limits on B(H→ 2γd+X) for FRVZ processes with a 125 GeV Higgs...

  • Auxiliary figure 6a

    Data from auxiliary figure 6a

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    Observed 95% CL upper limits on B(H→ 2γd+X) for different γd masses and a 125 GeV Higgs boson, as a function of...

  • Auxiliary figure 6b

    Data from auxiliary figure 6b

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    Observed 95% CL upper limits on B(H→ 2γd+X) for different γd masses and a 125 GeV Higgs boson, as a function of...

  • Auxiliary figure 6c

    Data from auxiliary figure 6c

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    Observed 95% CL upper limits on B(H→ 2γd+X) for different γd masses and a 125 GeV Higgs boson, as a function of...

  • Auxiliary figure 6d

    Data from auxiliary figure 6d

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    Observed 95% CL upper limits on B(H→ 2γd+X) for different γd masses and a 125 GeV Higgs boson, as a function of...

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