Limits on heavy neutral lepton mixing parameters

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

INSPIRE   JSON  (beta) 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
$<0.1$ 95 1
AAD
2024BU
 ATLS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $20 - 50$ GeV
$<6 \times 10^{-4}$ 95 2
HAYRAPETYAN
2024AB
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $20 - 60$ GeV
$<0.1$ 95 2
HAYRAPETYAN
2024AB
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}{ {}\gtrsim{} }{\mathit m}_{{{\mathit W}}}$
$<3 \times 10^{-4}$ 95 3
HAYRAPETYAN
2024S
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 2 GeV
$<0.01$ 95 4
HAYRAPETYAN
2024V
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $3 - 20$ GeV
$<1 \times 10^{-3}$ 90 5
NAYAK
2024
BELL Near ${\mathit m}_{{{\mathit \tau}}}–{\mathit m}_{{{\mathit \pi}}}$ kin. thres.
$<1 \times 10^{-5}$ 95 6
LEES
2023A
 BABR Near ${\mathit m}_{{{\mathit \tau}}}$ $−$ 3${\mathit m}_{{{\mathit \pi}}}$ kin. thres.
$<2 \times 10^{-6}$ 90 7
BAROUKI
2022
RVUE Near ${\mathit m}_{{{\mathit \tau}}}–{\mathit m}_{{{\mathit \nu}}}$ kin. thres.
$<3 \times 10^{-4}$ 90 8
ACCIARRI
2021
ARNT Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}{ {}\lesssim{} }$ 970 MeV
$<3 \times 10^{-6}$ 90 9
BOIARSKA
2021
RVUE Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $0.8 - 1.6$ GeV
$<2 \times 10^{-4}$ 90 10
ORLOFF
2002
CHRM Near ${\mathit m}_{{{\mathit D}}}−{\mathit m}_{{{\mathit \tau}}}$ kin. thres.
$<1 \times 10^{-4}$ 90 11
ORLOFF
2002
CHRM ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $200 - 250$ MeV
$<3 \times 10^{-5}$ 95 12
ABREU
1997I
 DLPH ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $6 - 50$ GeV
$<2 \times 10^{-5}$ 95 13
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. • •
14
LIVENTSEV
2023
BELL Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $0.8 - 1.2$ GeV
15
TUMASYAN
2022H
 CMS ${{\mathit p}}{{\mathit p}}$ at 13 TeV
1  AAD 2024BU search for same-sign tau pairs in semileptonic decays of top quarks via a Majorana HNL, in the HNL mass range $15 - 75$ GeV.
2  HAYRAPETYAN 2024AB search for ${{\mathit W}}$ $\rightarrow$ ${{\mathit \tau}}{{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit \tau}}{{\mathit \tau}}{{\mathit \ell}}{{\mathit \nu}_{{{{{\mathit \ell}}}}}}$ prompt decays assuming coupling to a single SM generation, between $10 - 1500$ GeV. Above ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ > ${\mathit m}_{{{\mathit W}}}$, sensitivity is greatly reduced by the required virtuality of the HNL. Results are quoted for a mass range below ${\mathit m}_{{{\mathit W}}}$ and just above ${\mathit m}_{{{\mathit W}}}$, for Majorana HNLs. Similar (weaker) limits also for Dirac HNLs are presented.
3  HAYRAPETYAN 2024S search for ${{\mathit W}}$ $\rightarrow$ ${{\mathit \tau}}{{\mathit \nu}_{{{x}}}}$ followed by ${{\mathit \nu}_{{{x}}}}$ displaced decay in flight to electromagnetic and hadronic showers in the CMS muon chamber, in the mass range ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $1 - 2$ GeV. Limits are set for both Majorana and Dirac HNLs. This long-lived particle style search results in an exclusion region in the coupling-mass plane whose upper contour is determined by an insufficiently long HNL lifetime to reach the muon chambers, and lower contour by insufficient HNL production. The intersection of these, and thus the extent of the experimental sensitivity, occurs at ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 2 GeV.
4  HAYRAPETYAN 2024V searches for ${{\mathit W}}$ $\rightarrow$ ${{\mathit \tau}}{{\mathit \nu}_{{{x}}}}$ with displaced decay ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit \tau}}{{\mathit j}}$, i.e. with one jet, over the range ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $3 - 20$ GeV. Limits are set for both Dirac and Majorana HNLs.
5  NAYAK 2024 searches for ${{\mathit \tau}}$ $\rightarrow$ ${{\mathit \pi}}{{\mathit \nu}_{{{x}}}}$ with displaced decay ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit \nu}_{{{\tau}}}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ in the Belle central drift chamber (CDC). This long-lived particle style search results in an exclusion region in the coupling-mass plane whose upper contour is determined by an insufficiently long HNL lifetime to reach the CDC, and lower contour by insufficient HNL production. Limits are set for both Dirac and Majorana HNLs.
6  Search for ${{\mathit \tau}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \nu}_{{{x}}}}$.
7  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.
8  Search for ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \nu}}$.
9  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.
10  ${{\mathit D}_{{{s}}}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ decay via ${{\mathit U}}_{{{\mathit \tau}} {{\mathit x}}}$.
11  ${{\mathit D}_{{{s}}}}$ $\rightarrow$ ${{\mathit \nu}_{{{\tau}}}}{{\mathit \tau}^{+}}$, ${{\mathit \tau}^{+}}$ $\rightarrow$ ${{\mathit \nu}_{{{x}}}}{{\mathit X}}$, with ${{\mathit \nu}_{{{x}}}}$ decay via ${{\mathit U}}_{{{\mathit \tau}} {{\mathit x}}}$.
12  Search for prompt ${{\mathit \nu}_{{{x}}}}$ decay signatures.
13  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 $.
14  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.
15  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