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Search for exotic decays of the Higgs boson into long-lived particles in $pp$ collisions at $\sqrt{s} = 13$ TeV using displaced vertices in the ATLAS inner detector

The ATLAS collaboration
2021.

Abstract (data abstract)
CERN-LHC. A novel search for exotic decays of the Higgs boson into pairs of long-lived neutral particles, each decaying into a bottom quark pair, is performed using 139 fb$^{-1}$ of $\sqrt{s} = 13$ TeV proton--proton collision data collected with the ATLAS detector at the LHC. Events consistent with the production of a Higgs boson in association with a leptonically decaying $Z$ boson are analysed. Long-lived particle (LLP) decays are reconstructed from inner-detector tracks as displaced vertices with high mass and track multiplicity relative to Standard Model processes. The analysis selection requires the presence of at least two displaced vertices, effectively suppressing Standard Model backgrounds. The residual background contribution is estimated using a data-driven technique. No excess over Standard Model predictions is observed, and upper limits are set on the branching ratio of the Higgs boson to LLPs. Branching ratios above $10\%$ are excluded at $95\%$ confidence level for LLP mean proper lifetimes $c\tau$ as small as 4 mm and as large as 102 mm. For LLP masses below 40 GeV, these results represent the most stringent constraint in this lifetime regime.

  • Table 1

    Data from Auxillary Figure 2A

    10.17182/hepdata.106655.v1/t1

    95% CL exclusion limits on $\mathcal{B}(H\rightarrow aa \rightarrow b\bar{b}b\bar{b})$ for $m_a = 16$ GeV.

  • Table 2

    Data from Auxillary Figure 2B

    10.17182/hepdata.106655.v1/t2

    95% CL exclusion limits on $\mathcal{B}(H\rightarrow aa \rightarrow b\bar{b}b\bar{b})$ for $m_a = 25$ GeV.

  • Table 3

    Data from Auxillary Figure 2C

    10.17182/hepdata.106655.v1/t3

    95% CL exclusion limits on $\mathcal{B}(H\rightarrow aa \rightarrow b\bar{b}b\bar{b})$ for $m_a = 35$ GeV.

  • Table 4

    Data from Auxillary Figure 2D

    10.17182/hepdata.106655.v1/t4

    95% CL exclusion limits on $\mathcal{B}(H\rightarrow aa \rightarrow b\bar{b}b\bar{b})$ for $m_a = 45$ GeV.

  • Table 5

    Data from Auxillary Figure 2E

    10.17182/hepdata.106655.v1/t5

    95% CL exclusion limits on $\mathcal{B}(H\rightarrow aa \rightarrow b\bar{b}b\bar{b})$ for $m_a = 55$ GeV.

  • Table 6

    Data from Auxillary Figure 1

    10.17182/hepdata.106655.v1/t6

    The fraction of $a$ boson decays matched to reconstructed displaced vertices passing all vertex selections in signal MC.

  • Table 7

    Data from Auxillary Figure 7

    10.17182/hepdata.106655.v1/t7

    The extrapolated signal selection efficiency as a function of $c\tau_{a}$.

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