Search for heavy neutral leptons in decays of $W$ bosons produced in 13 TeV $pp$ collisions using prompt and displaced signatures with the ATLAS detector

The ATLAS collaboration
JHEP 1910 (2019) 265, 2019.

Abstract (data abstract)
The problems of neutrino masses, matter–antimatter asymmetry, and dark matter could be successfully addressed by postulating right-handed neutrinos with Majorana masses below the electroweak scale. In this work, leptonic decays of W bosons extracted from 32.9 fb$^{−1}$ to 36.1 fb$^{-1}$ of 13 TeV proton–proton collisions at the LHC are used to search for heavy neutral leptons (HNLs) that are produced through mixing with muon or electron neutrinos. The search is conducted using the ATLAS detector in both prompt and displaced leptonic decay signatures. The prompt signature requires three leptons produced at the interaction point (either µµe or eeµ) with a veto on same-flavour opposite-charge topologies. The displaced signature comprises a prompt muon from the W boson decay and the requirement of a dilepton vertex (either $\mu\mu$ or $\mu e$) displaced in the transverse plane by 4–300 mm from the interaction point. The search sets constraints on the HNL mixing to muon and electron neutrinos for HNL masses in the range 4.5–50 GeV.

  • Table 1

    Fig 2

    10.17182/hepdata.91136.v1/t1

    Displaced HNL event selection efficiency as a function of mean proper decay length for HNL mass 5, 7.5, 10 and...

  • Table 2

    Fig 2

    10.17182/hepdata.91136.v1/t2

    Prompt HNL event selection efficiency as a function of mean proper decay length for HNL mass 10 GeV.

  • Table 3

    Fig 6(a)

    10.17182/hepdata.91136.v1/t3

    Displaced HNL search observed 95% confidence level exclusion contour in $|U_{\mu}|^2$ as a function of HNL mass (LNC case).

  • Table 4

    Fig 6(a)

    10.17182/hepdata.91136.v1/t4

    Displaced HNL search observed 95% confidence level exclusion contour in $|U_{\mu}|^2$ as a function of HNL mass (LNV case).

  • Table 5

    Fig 6(b)

    10.17182/hepdata.91136.v1/t5

    Prompt HNL search observed and expected 95% confidence level exclusion upper limits in $|U_{e}|^2$ as a function of HNL mass.

  • Table 6

    Fig 6(a)

    10.17182/hepdata.91136.v1/t6

    Prompt HNL search observed and expected 95% confidence level exclusion upper limits in $|U_{\mu}|^2$ as a function of HNL mass.

  • Table 7

    Fig 6(a)

    10.17182/hepdata.91136.v1/t7

    Displaced HNL search expected 95% confidence level exclusion contour in $|U_{\mu}|^2$ as a function of HNL mass (LNC case).

  • Table 8

    Fig 6(a)

    10.17182/hepdata.91136.v1/t8

    Displaced HNL search expected 95% confidence level exclusion contour in $|U_{\mu}|^2$ as a function of HNL mass (LNV case).

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