Limits on heavy neutral lepton mixing parameters

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

INSPIRE  
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
$<1 \times 10^{-3}$ 95 1
AAIJ
2021AA
 LHCB ${\mathit m}_{{{\mathit \nu}_{{x}}}}\sim{}5 - 50$ GeV, ${{\mathit p}}{{\mathit p}}$ at 7, 8 TeV
$<2 \times 10^{-4}$ 95 2
AAIJ
2021AA
 LHCB ${\mathit m}_{{{\mathit \nu}_{{x}}}}\sim{}5 - 50$ GeV, ${{\mathit p}}{{\mathit p}}$ at 7, 8 TeV
$<5 \times 10^{-9}$ 90 3, 4
CORTINA-GIL
2021
NA62 Near ${\mathit m}_{{{\mathit K}}}–{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
$<1 \times 10^{-7}$ 90 5
ABRATENKO
2020
MBNE Near ${\mathit m}_{{{\mathit K}}}–{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
$<0.02$ 90 6
PRIM
2020
BELL ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ 1 GeV
$<2 \times 10^{-5}$ 95 7
AAD
2019F
 ATLS ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ $10 - 50$ GeV
$<2 \times 10^{-6}$ 95 8
AAD
2019F
 ATLS ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ 10 GeV
$<1 \times 10^{-9}$ 90 9
ABE
2019B
 T2K Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
$<5 \times 10^{-6}$ 90 10, 11
AGUILAR-AREVA..
2019B
 PIEN ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ $16 - 30$ MeV
$<1 \times 10^{-5}$ 90 11
AGUILAR-AREVA..
2019B
 PIEN Near ${\mathit m}_{{{\mathit \pi}}}−{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
$<3 \times 10^{-7}$ 90 3
CORTINA-GIL
2018
NA62 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ $250 - 350$ MeV
$<3 \times 10^{-6}$ 90 3
LAZZERONI
2017A
 NA62 Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
$<0.05$ 90 12
PARK
2016
BELL ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ 1.4 GeV
$<1 \times 10^{-8}$ 90 3
ARTAMONOV
2015A
 B949 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ $200 - 300$ MeV
$<3 \times 10^{-5}$ 90 13
LIVENTSEV
2013
BELL Near ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ $2 - 2.5$ GeV
$<2.0 \times 10^{-8}$ 95 14
DAUM
2000
KARM ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ = 33.905 MeV
$<8 \times 10^{-8}$ 90 15
VAITAITIS
1999
CCFR Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
$<6 \times 10^{-8}$ 90 16
VAITAITIS
1999
CCFR Near ${\mathit m}_{{{\mathit D}_{{s}}}}−{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
$<3 \times 10^{-5}$ 95 17
ABREU
1997I
 DLPH ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ $6 - 50$ GeV
$<2 \times 10^{-5}$ 95 18
ABREU
1997I
 DLPH Near ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ 3.5 GeV
$<3 \times 10^{-5}$ 90 19
VILAIN
1995C
 CHM2 Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
$<3 \times 10^{-8}$ 20, 21
BERNARDI
1988
CNTR Near ${\mathit m}_{{{\mathit \mu}}}+{\mathit m}_{{{\mathit \pi}}}$ kin. thres.
$<2 \times 10^{-9}$ 21, 22
BERNARDI
1988
CNTR Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
$<1 \times 10^{-7}$ 90 23
DORENBOSCH
1986
CHRM Near ${\mathit m}_{{{\mathit D}}}−{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
$<1 \times 10^{-7}$ 90 24
COOPER-SARKAR
1985
BEBC Near ${\mathit m}_{{{\mathit D}}}−{\mathit m}_{{{\mathit \mu}}}$ kin. thres.
1  Limit from prompt lepton number conserving ${{\mathit W}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit \mu}}{{\mathit j}}$ search.
2  Limit from prompt lepton number violating ${{\mathit W}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit \mu}}{{\mathit j}}$ search .
3  Search for ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ .
4  Assumes a lifetime exceeding 50 ns, and searches over ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ range $200 - 384$ MeV.
5  ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{-}}{{\mathit \pi}^{+}}$ , in the mass range ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ $260 - 385$ MeV. ABRATENKO 2020 also considers ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \pi}^{-}}$ for the case of Majorana HNL.
6  Search for ${{\mathit B}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ in the mass range ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $\sim{}$ $0 - 1.5$ GeV .
7  Limit from prompt lepton number violating trilepton search.
8  Limit from displaced lepton violating or conserving trilepton searches.
9  ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , 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.
10  Limit requires muon kinetic energy $>$ 1.2 MeV.
11  Search for ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ .
12  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.
13  Search for ${{\mathit B}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ .
14  DAUM 2000 quotes a branching ratio bound B( ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ ) $<$ $6.0 \times 10^{-10}$ at 95$\%$ CL.
15  ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit X}}$ .
16  ${{\mathit D}_{{s}}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit X}}$ .
17  Search for prompt ${{\mathit \nu}_{{x}}}$ decay signatures.
18  Search for displaced ${{\mathit \nu}_{{x}}}$ decay signatures.
19  Search for Heavy Neutral Leptons produced by neutral current muon neutrino interactions, with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}{{\mathit \nu}_{{\mu}}}$ .
20  ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ decay through ${{\mathit U}}$ $_{ {{\mathit \mu}} {{\mathit x}} }$ and ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $<$ ${\mathit m}_{{{\mathit \mu}}}$ + ${\mathit m}_{{{\mathit \pi}}}$.
21  BERNARDI 1988 also considers bounds on $\vert {{\mathit U}}$ $_{ {{\mathit e}} {{\mathit x}} }{{\mathit U}}$ $_{ {{\mathit \mu}} {{\mathit x}} }\vert $.
22  ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{-}}{{\mathit \pi}^{+}}$ .
23  ${{\mathit D}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{-}}{{\mathit \ell}^{+}}{{\mathit \nu}_{{{{\mathit \ell}}}}}$ .
24  ${{\mathit D}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{x}}}$ , with ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{-}}{{\mathit \ell}^{+}}{{\mathit \nu}_{{{{\mathit \ell}}}}}$ or ${{\mathit \nu}_{{x}}}$ $\rightarrow$ ${{\mathit \mu}^{-}}{{\mathit \pi}^{+}}$ .
References:
AAIJ 2021AA
EPJ C81 248 Search for heavy neutral leptons in $W^+\to\mu^{+}\mu^{\pm}\text{jet}$ decays
CORTINA-GIL 2021
PL B816 136259 Search for $K^+$ decays to a muon and invisible particles
ABRATENKO 2020
PR D101 052001 Search for Heavy Neutral Leptons Decaying into Muon-Pion Pairs in the MicroBooNE Detector
PRIM 2020
PR D101 032007 Search for $B^+ \to \mu^+\, \nu_\mu$ and $B^+ \to \mu^+\, N$ with inclusive tagging
AAD 2019F
JHEP 1910 265 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
ABE 2019B
PR D100 052006 Search for heavy neutrinos with the T2K near detector ND280
AGUILAR-AREVALO 2019B
PL B798 134980 Search for heavy neutrinos in $\pi \to \mu\nu$ decay
CORTINA-GIL 2018
PL B778 137 Search for heavy neutral lepton production in $K^+$ decays
LAZZERONI 2017A
PL B772 712 Search for Heavy Neutrinos in ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{\mu}}}$ Decays
PARK 2016
PR D94 012003 Search for a Massive Invisible Particle ${{\mathit X}^{0}}$ in ${{\mathit B}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit X}^{0}}$ and ${{\mathit B}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit X}^{0}}$ Decays
ARTAMONOV 2015A
PR D91 052001 Search for Heavy Neutrinos in ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{H}}}$ Decays
LIVENTSEV 2013
PR D87 071102 Search for Heavy Neutrinos at Belle
Also
PR D95 099903 (errat.) Erratum to LIVENTSEV 2013 : Search for Heavy Neutrinos at Belle
DAUM 2000
PRL 85 1815 The KARMEN Time Anomaly: Search for a Neutral Particle of Mass 33.9 MeV in Pion Decay
VAITAITIS 1999
PRL 83 4943 Search for Neutral Heavy Leptons in a High Energy Neutrino Beam
ABREU 1997I
ZPHY C74 57 Search for Neutral Heavy Leptons Produced in ${{\mathit Z}}$ Decays
Also
ZPHY C75 580 (errat.) Erratum: ABREU 1997I Search for Neutral Heavy Leptons Produced in ${{\mathit Z}}$ Decays
VILAIN 1995C
PL B351 387 Search for Heavy Isosinglet Neutrinos
Also
PL B343 453 Search for Heavy Isosinglet Neutrinos
BERNARDI 1988
PL B203 332 Further Limit on Heavy Neutrino Coupling
DORENBOSCH 1986
PL 166B 473 A Search for Decays of Heavy Neutrinos in the Mass Range of 0.5 $−$ 2.8 GeV
COOPER-SARKAR 1985
PL 160B 207 Search for Heavy Neutrino Decays in the BEBC Beam Dump Experiment