| $<2 \times 10^{-5}$ |
95 |
1 |
|
ATLS |
| $<2 \times 10^{-6}$ |
95 |
2 |
|
ATLS |
| $<1 \times 10^{-9}$ |
90 |
3 |
|
T2K |
| $<5 \times 10^{-6}$ |
90 |
4, 5 |
|
PIEN |
| $<1 \times 10^{-5}$ |
90 |
5 |
|
PIEN |
| $<3 \times 10^{-7}$ |
90 |
6 |
|
NA62 |
| $<3 \times 10^{-6}$ |
90 |
6 |
|
NA62 |
| $<1 \times 10^{-8}$ |
90 |
6 |
|
B949 |
| $<2.0 \times 10^{-8}$ |
95 |
7 |
|
KARM |
| $<8 \times 10^{-8}$ |
90 |
8 |
|
CCFR |
| $<6 \times 10^{-8}$ |
90 |
9 |
|
CCFR |
| $<3 \times 10^{-5}$ |
95 |
10 |
|
DLPH |
| $<2 \times 10^{-5}$ |
95 |
11 |
|
DLPH |
| $<3 \times 10^{-5}$ |
90 |
12 |
|
CHM2 |
| $<3 \times 10^{-8}$ |
|
13, 14 |
|
CNTR |
| $<2 \times 10^{-9}$ |
|
14, 15 |
|
CNTR |
| $<1 \times 10^{-7}$ |
90 |
16 |
|
CHRM |
| $<1 \times 10^{-7}$ |
90 |
17 |
|
BEBC |
| • • • We do not use the following data for averages, fits, limits, etc. • • • |
|
|
18 |
|
BELL |
|
1
Limit from prompt lepton number violating trilepton search.
|
|
2
Limit from displaced lepton violating or conserving trilepton searches.
|
|
3
${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ decay through ${{\mathit U}}_{ {{\mathit \mu}} {{\mathit x}} }$. ABE 2019B also considers bounds on $\vert {{\mathit U}}_{ {{\mathit \ell}} {{\mathit x}} }{{\mathit U}}_{ {{\mathit \ell}^{\,'}} {{\mathit x}} }\vert $ for combinations of lepton flavors in the ${{\mathit \nu}_{{x}}}$ decay final state.
|
|
4
Limit requires muon kinetic energy $>$ 1.2 MeV.
|
|
5
Search for ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ .
|
|
6
Search for ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ .
|
|
7
DAUM 2000 quotes a branching ratio bound B( ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ ) $<$ $6.0 \times 10^{-10}$ at 95$\%$ CL.
|
|
8
${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit X}}$ .
|
|
9
${{\mathit D}_{{s}}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit X}}$ .
|
|
10
Search for prompt ${{\mathit \nu}_{{x}}}$ decay signatures.
|
|
11
Search for displaced ${{\mathit \nu}_{{x}}}$ decay signatures.
|
|
12
Search for Heavy Neutral Leptons produced by neutral current muon neutrino interactions, with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \nu}_{{\mu}}}$ .
|
|
13
${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ decay through ${{\mathit U}}_{ {{\mathit \mu}} {{\mathit x}} }$ and ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $<$ ${\mathit m}_{{{\mathit \mu}}}$ + ${\mathit m}_{{{\mathit \pi}}}$.
|
|
14
BERNARDI 1988 also considers bounds on $\vert {{\mathit U}}_{ {{\mathit e}} {{\mathit x}} }{{\mathit U}}_{ {{\mathit \mu}} {{\mathit x}} }\vert $.
|
|
15
${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{-}}{{\mathit \pi}^{+}}$ .
|
|
16
${{\mathit D}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{-}}{{\mathit \ell}^{+}}{{\mathit \nu}_{{{{\mathit \ell}}}}}$ .
|
|
17
${{\mathit D}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{-}}{{\mathit \ell}^{+}}{{\mathit \nu}_{{{{\mathit \ell}}}}}$ or ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{-}}{{\mathit \pi}^{+}}$ .
|
|
18
PARK 2016 quotes an approximate limit B( ${{\mathit B}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ ) $<$ $3 \times 10^{-6}$ in the mass range ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ $0.2 - 1.4$ GeV.
|
