Blast from the past II: Constraints on heavy neutral leptons from the BEBC WA66 beam dump experiment

Abstract

We revisit the search for heavy neutral leptons with the Big European Bubble Chamber in the 1982 proton beam dump experiment at CERN, focussing on those heavier than the kaon and mixing only with the tau neutrino, as these are far less constrained than their counterparts with smaller mass or other mixings. Recasting the previous search in terms of this model and including additional production and decay channels yields the strongest bounds to date, up to the tau mass. This applies also to our updated bounds on the mixing of heavy neutral leptons with the electron neutrino.

Search for Heavy Neutral Leptons in $tau$-lepton decays with the $BABAR$ detector.

“…In 2021 the ArgoNeuT experiment 24 also published limits in this region, the BABAR result improves on those limits. In a recent publication Barouki et al 25 showed even tighter bounds. In addition, a recent recasting of the CHARM data, which utilizes data from the electron and muon searches to indirectly constrain the tau sector, has also improved constraints in the same region 26 .…”

Feebly-interacting particles: FIPs 2020 workshop report

“…The dashed seesaw line is given by |U α | 2 = ∆m 2 atm /m N corresponding to the naive seesaw scaling and should be considered only as indicative. [1432] and BEBC (recasted) [1764]; ArgoNeut [1781]; BaBar [1612]; DELPHI [1788]; T2K [1786] Coloured curves are projections from: HIKE-dump [1392], SHiP [1402], DarkQuest [1257], Belle II [1782], DUNE [1172], FASER2 [1416]; CODEX-b [1030], and MATHUSLA200 [1441]. The BBN bounds are from [1686].…”

“…Such models have open parameter space where the heavy neutral leptons (HNL) mix only with a single flavour of active neutrinos [1763]. We have carried out work studying the currently least constrained possibility of mixing between HNLs and the tau neutrino [1764]. In this simple model, an HNL N has a mass m N and mixes with the ν τ with a strength given by U τ N .…”

“…Legend: filled gray areas are bounds coming from interpretation of old data sets or astrophysical data; filled coloured areas are bounds set by experimental collaborations; Solid coloured lines are projections based on existing data sets; Dashed coloured lines are projections based on full Monte Carlo simulations; Dotted coloured lines are projections based on toy Monte Carlo simulations. Filled areas are existing bounds from: CHARM (recasted)[1432] and BEBC (recasted)[1764]; ArgoNeut[1781]; BaBar[1612]; DELPHI[1788]; T2K[1786] Coloured curves are projections from: HIKE-dump[1392], SHiP[1402], DarkQuest[1257], Belle II[1782], DUNE[1172], FASER2 [1416]; CODEX-b[1030], and MATHUSLA200[1441]. The BBN bounds are from[1686].…”

Heavy neutral leptons at beam dump experiments of future lepton colliders

“…The gray shaded regions are the leading existing constraints from PIENU [78,79], PS191 [13, (although these constraints have recently been reanalyzed and found to be weaker; see [80] for more details), NA62 [81], CHARM [82], BEBC [83,84], Belle [43], DEL-PHI [85], and ATLAS [86] for electron-mixed HNLs; E949 [87], PS191 [13,14], T2K [16,17], NuTeV [88], CHARM [89], Belle [43], DELPHI [85], and ATLAS [86] for muon-mixed HNLS; and NOMAD [15], CHARM [12,15,90], BEBC [84], ArgoNeuT [20], and DELPHI [85] for τ -mixed HNLs. The shaded blue regions at small mixing angles are additional constraints from Big Bang nucleosynthesis (BBN) studies [91,92].…”