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

Abstract

Search for heavy neutral leptons in decays of W bosons produced in 13 TeV p p collisions using prompt and displaced signatures with the ATLAS detectorThe ATLAS CollaborationThe 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 µµ or µe) 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.

Exotic lepton-flavor violating Higgs decays

“…[97][98][99], others are focused on displaced ee or µµ signatures, e.g. [100,101], and others target fairly specific signatures [102]. Recasting these studies is beyond the scope of this work, but we note that scalars with an lfv decay in these models can easily be displaced and are not optimally constrained by existing searches.…”

Neutrinoless double beta decay versus other probes of heavy sterile neutrinos

“…For a given mixing, m N must lie in a specific range in order to avoid N decaying promptly or outside the detector. The best projected limit is |V eN | 2 , |V µN | 2 10 −9 for m N ≈ 30 GeV [56].…”

“…CMS broadened the search to the LNC channel with a sensitivity to displaced decays. The analyses impose the limits |V eN | 2 , |V µN | 2 < 10 −5 − 10 −4 over the mass range 5 GeV < m N < 50 GeV [56,57]. ATLAS and CMS have also conducted searches for the LNV same-sign dilepton + jets channel, W ± → ± N, N → ± jj [58,59].…”

“…13 the constraints from a variety of experiments on the m N − |V µN | 2 and m N − |V τ N | 2 parameter spaces (above and below respectively). Upper limits on the muon-sterile mixing strength have been placed above m N ∼ 1 MeV by PSI [215], PIENU [216], KEK [217,218], PS191 [95], measurements of the muon decay spectrum [219], Super-Kamiokande [220], E949 [221], NA62 [222], T2K [97], Micro-BooNE [223], a variety of LNV meson decays [39,82,102,103], NuTeV [224], BEBC [225], FMMF [226], NA3 [92], CHARM [94], LHCb [227], Belle [91], ATLAS [56], CMS [57], L3 [63], DELPHI [65] and electroweak precision data [134,135,137,138]. In the light regime, i.e.…”

A model for lepton flavor violating non-standard neutrino interactions

“…In the literature, strong bounds on the mixing of sterile neutrinos with mass heavier than 500 MeV with active neutrinos have also been reported from NuTeV [12], WA66 [13], CHARM II [14], BELLE [15], Higgs decay [16], NA62 [17], L3 [18], DELPHI [19] and ATLAS+CMS [20]. Ref.…”