Search for short- and long-lived axion-like particles in Haa4γ decays with the ATLAS experiment at the LHC

The ATLAS collaboration
Eur.Phys.J.C 84 (2024) 742, 2024.

Abstract (data abstract)
A search for anomalous Higgs boson decays into two axion-like particles (ALPs) using the full Run~2 data set recorded by the ATLAS experiment is presented. The ALPs are assumed to decay into two photons, providing sensitivity to recently proposed models that could explain the (g2)μ discrepancy. This analysis covers an ALP mass range from 100MeV to 62GeV and ALP-photon couplings in the range 105TeV1<Caγγ/Λ<1TeV1, and therefore includes signatures with significantly displaced vertices and highly collinear photons. No significant excess of events above the Standard Model background is observed. Upper limits at 95% confidence level are placed on the branching ratio of the Higgs boson to two ALPs in the four-photon final state, and are in the range of 105 to 3×102, depending on the hypothesized ALP mass and ALP-photon coupling strength.

  • Signal cut-flow

    Data from AuxTables 1-6.

    10.17182/hepdata.144534.v1/t1

    Cut-flow and number of events in a region with 110 GeV<maa<130 GeV for selected signal samples

  • Systematic uncertainties

    Data from AuxTable 7.

    10.17182/hepdata.144534.v1/t2

    Overview of relative systematic uncertainties on the signal normalization for selected couplings and mass points in the dominant categories. All...

  • Exclusion limits for Caγγ=1

    Data from Figure 6a.

    10.17182/hepdata.144534.v1/t3

    Upper limits on B(Haa4γ) at 95% CL as a function of the axion mass and for ALP-photon coupling...

  • Exclusion limits for Caγγ=0.01

    Data from Figure 6b.

    10.17182/hepdata.144534.v1/t4

    Upper limits on B(Haa4γ) at 95% CL as a function of the axion mass and for ALP-photon coupling...

  • Exclusion limits for Caγγ=5×104

    Data from Figure 6c.

    10.17182/hepdata.144534.v1/t5

    Upper limits on B(Haa4γ) at 95% CL as a function of the axion mass and for ALP-photon coupling...

  • Exclusion limits for Caγγ=105

    Data from Figure 6d.

    10.17182/hepdata.144534.v1/t6

    Upper limits on B(Haa4γ) at 95% CL as a function of the axion mass and for ALP-photon coupling...

  • Exclusion limits for prompt analysis

    Data from Figure 8.

    10.17182/hepdata.144534.v1/t7

    Upper limits on B(H4γ) at 95% CL as a function of the signal mass hypothesis and for the assumption...

  • Tight efficiency

    Data from Auxiliary Figure 5a.

    10.17182/hepdata.144534.v1/t8

    Identification efficiency for isolated photons that pass the tight photon ID requirements in dependence of the opening angle in $\Delta...

  • Merged efficiency

    Data from Auxiliary Figure 5b.

    10.17182/hepdata.144534.v1/t9

    Efficiency for classified merged isolated photons in dependence of the opening angle in ΔR of both decay photons of...

  • 2D exclusion limits

    Data from Figure 9.

    10.17182/hepdata.144534.v1/t10

    Limits on the ALP mass and coupling to photons at 95\%~CL, assuming B(aγγ)=1, Λ=1TeV with |CaHeff|...

  • Data background comparison

    Data from Figure 5.

    10.17182/hepdata.144534.v1/t11

    The number of data and estimated background events in the signal region of the most sensitive categories..

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