Limits on heavy neutral lepton mixing parameters

Limits on $\vert {{\mathit U}}_{{{\mathit \tau}} {{\mathit x}}}\vert ^2$

INSPIRE   PDGID:
S077A02
Quoted limits are either the best limit near the kinematic threshold of the experiment, or a characteristic value in the mass range of the experimental sensitivity
VALUE CL% DOCUMENT ID TECN  COMMENT
$<1 \times 10^{-5}$ 95 1
LEES
2023A
 BABR Near ${\mathit m}_{{{\mathit \tau}}}$ $−$ 3${\mathit m}_{{{\mathit \pi}}}$ kin. thres.
$<2 \times 10^{-6}$ 90 2
BAROUKI
2022
RVUE Near ${\mathit m}_{{{\mathit \tau}}}–{\mathit m}_{{{\mathit \nu}}}$ kin. thres.
$<3 \times 10^{-4}$ 90 3
ACCIARRI
2021
ARNT Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}{ {}\lesssim{} }$ 970 MeV
$<3 \times 10^{-6}$ 90 4
BOIARSKA
2021
RVUE Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $0.8 - 1.6$ GeV
$<2 \times 10^{-4}$ 90 5
ORLOFF
2002
CHRM Near ${\mathit m}_{{{\mathit D}}}−{\mathit m}_{{{\mathit \tau}}}$ kin. thres.
$<1 \times 10^{-4}$ 90 6
ORLOFF
2002
CHRM ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $200 - 250$ MeV
$<3 \times 10^{-5}$ 95 7
ABREU
1997I
 DLPH ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $6 - 50$ GeV
$<2 \times 10^{-5}$ 95 8
ABREU
1997I
 DLPH Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 3.5 GeV
• • We do not use the following data for averages, fits, limits, etc. • •
9
LIVENTSEV
2023
BELL Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $0.8 - 1.2$ GeV
10
TUMASYAN
2022H
 CMS ${{\mathit p}}{{\mathit p}}$ at 13 TeV
1  Search for ${{\mathit \tau}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \nu}_{{{x}}}}$.
2  Reanalysis of BEBC results (cf. COOPER-SARKAR 1985) to include searches for ${{\mathit D}_{{{s}}}^{\pm}}$ $\rightarrow$ ${{\mathit \nu}_{{{\tau}}}}{{\mathit \tau}^{\pm}}$, ${{\mathit \tau}^{\pm}}$ $\rightarrow$ ${{\mathit \nu}_{{{x}}}}{{\mathit \pi}^{\pm}}$, ${{\mathit \nu}_{{{x}}}}{{\mathit \rho}^{\pm}}$, or ${{\mathit \nu}_{{{x}}}}{{\mathit \nu}_{{{\tau}}}}{{\mathit \ell}^{\pm}}$ via ${{\mathit U}}_{{{\mathit \tau}} {{\mathit x}}}$. Assumes a Majorana HNL.
3  Search for ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \nu}}$.
4  Reanalysis of CHARM results (cf. ORLOFF 2002) to include searches for ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit \ell}^{+}}{{\mathit \ell}^{-}}$ decays, and including the production of HNLs from ${{\mathit \tau}}$ decays.
5  ${{\mathit D}_{{{s}}}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ decay via ${{\mathit U}}_{{{\mathit \tau}} {{\mathit x}}}$.
6  ${{\mathit D}_{{{s}}}}$ $\rightarrow$ ${{\mathit \nu}_{{{\tau}}}}{{\mathit \tau}^{+}}$, ${{\mathit \tau}^{+}}$ $\rightarrow$ ${{\mathit \nu}_{{{x}}}}{{\mathit X}}$, with ${{\mathit \nu}_{{{x}}}}$ decay via ${{\mathit U}}_{{{\mathit \tau}} {{\mathit x}}}$.
7  Search for prompt ${{\mathit \nu}_{{{x}}}}$ decay signatures.
8  Search for displaced ${{\mathit \nu}_{{{x}}}}$ decay signatures. Kinematical suppression of ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit \tau}}{{\mathit X}}$ at lower masses leads to rapid loosening of the $\vert {{\mathit U}}_{{{\mathit \tau}} {{\mathit x}}}\vert $ bound compared to that for $\vert {{\mathit U}}_{{{\mathit e}} {{\mathit x}}}\vert $ and $\vert {{\mathit U}}_{{{\mathit \mu}} {{\mathit x}}}\vert $.
9  Search for ${{\mathit \tau}}$ $\rightarrow$ ${{\mathit \pi}}{{\mathit \nu}_{{{x}}}}$ , ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit \pi}}{{\mathit e}}$ or ${{\mathit \pi}}{{\mathit \mu}}$ in the range $0.2 - 1.6$ GeV. LIVENTSEV 2023 reports results for the sum $\Sigma _{{{\mathit \ell}}={{\mathit e}},{{\mathit \mu}},{{\mathit \tau}}}\vert {{\mathit U}}_{{{\mathit \ell}} {{\mathit x}}}\vert ^2$ in a model-dependent context, but which may be roughly reinterpreted as a limit $\vert {{\mathit U}}_{{{\mathit e}} {{\mathit x}}}{{\mathit U}}_{{{\mathit \tau}} {{\mathit x}}}\vert ^2$ + $\vert {{\mathit U}}_{{{\mathit \mu}} {{\mathit x}}}{{\mathit U}}_{{{\mathit \tau}} {{\mathit x}}}\vert ^2$ ${ {}\lesssim{} }$ $5 \times 10^{-9}$ in either Majorana or Dirac HNL scenarios.
10  TUMASYAN 2022H sets limits on an approximately mass-degenerate vector-like lepton SU(2) doublet coupling to the ${{\mathit \tau}}$. Some of the reported signal region distributions might be used to set limits for heavy neutral leptons coupled to the ${{\mathit \tau}}$. The data correspond to an integrated luminosity of 138 fb${}^{-1}$.
References