Limits on heavy neutral lepton mixing parameters

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

INSPIRE   PDGID:
S077A00
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
$<5 \times 10^{-7}$ 95 1
AAD
2023AO
 ATLS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}\sim{}3 - 15$ GeV, ${{\mathit p}}{{\mathit p}}$ at 13 TeV
$<3 \times 10^{-4}$ 90 2
AGNES
2023A
 DS50 ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $7 - 35$ keV
$<3 \times 10^{-8}$ 90 3
BAROUKI
2022
RVUE Near ${\mathit m}_{{{\mathit D}_{{{s}}}}}–{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<1 \times 10^{-6}$ 95 4
TUMASYAN
2022AD
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}\sim{}8 - 14$ GeV, ${{\mathit p}}{{\mathit p}}$ at 13 TeV
$<2 \times 10^{-4}$ 95 5
FRIEDRICH
2021
Near ${\mathit m}_{\mathrm {{}^{7}\mathrm {Be}}}−$ ${\mathit m}_{\mathrm {{}^{7}\mathrm {Li}}}$ kin. thres.
$<1 \times 10^{-9}$ 90 6
CORTINA-GIL
2020
NA62 ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $150 - 400$ MeV
$<2 \times 10^{-5}$ 95 7
AAD
2019F
 ATLS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $15 - 40$ GeV
$<1 \times 10^{-9}$ 90 8
ABE
2019B
 T2K Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<1 \times 10^{-4}$ 90 9
ABLIKIM
2019AL
 BES3 ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $0.3 - 0.7$ GeV
$<2 \times 10^{-7}$ 90 10
BRYMAN
2019
RVUE ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}\sim{}$ 55 MeV
$<1 \times 10^{-8}$ 90 11
AGUILAR-AREVA..
2018A
 PIEN ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $60 - 120$ MeV
$<3 \times 10^{-7}$ 90 12
CORTINA-GIL
2018
NA62 ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $200 - 400$ MeV
$<1 \times 10^{-6}$ 90 13
PARK
2016
BELL ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 1.4 GeV
$<3 \times 10^{-5}$ 90 14
LIVENTSEV
2013
BELL Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $2 - 2.5$ GeV
$<3 \times 10^{-5}$ 95 15
ABREU
1997I
 DLPH ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $6 - 50$ GeV
$<2 \times 10^{-5}$ 95 16
ABREU
1997I
 DLPH Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 3.5 GeV
$<1 \times 10^{-5}$ 90 17
BARANOV
1993
Near ${\mathit m}_{{{\mathit \pi}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<2 \times 10^{-7}$ 90 17
BARANOV
1993
Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<1 \times 10^{-7}$ 18, 19
BERNARDI
1988
CNTR Near ${\mathit m}_{{{\mathit \pi}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<2 \times 10^{-9}$ 20, 19
BERNARDI
1988
CNTR Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<1 \times 10^{-7}$ 90 21
DORENBOSCH
1986
CHRM Near ${\mathit m}_{{{\mathit D}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<1 \times 10^{-7}$ 90 22
COOPER-SARKAR
1985
BEBC Near ${\mathit m}_{{{\mathit D}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
1  AAD 2023AO search for ${{\mathit W}}$ $\rightarrow$ ${{\mathit \nu}_{{{x}}}}{{\mathit e}}$, for both Majorana and Dirac HNL scenarios. Also consider scenarios involving multiflavor mixing, with correspondingly weaker limits.
2  Search for ionization signals in an LArTPC. Assumes the candidate particle is 100$\%$ of dark matter.
3  Reanalysis of BEBC results (cf. COOPER-SARKAR 1985) to update searches for ${{\mathit D}_{{{s}}}^{\pm}}$ $\rightarrow$ ${{\mathit \nu}_{{{x}}}}{{\mathit e}^{\pm}}$ using a corrected formula for the HNL decay probabilities, additional production channels, and an improved fit for the charm meson distributions. Assumes a Majorana HNL.
4  TUMASYAN 2022AD search for ${{\mathit W}}$ $\rightarrow$ ${{\mathit e}}{{\mathit \nu}_{{{x}}}}$, ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}}{{\mathit \mu}}{{\mathit \nu}_{{{\mu}}}}$ and set limits for Dirac and Majorana Heavy Neutral Leptons. The data correspond to an integrated luminosity of 138 fb${}^{-1}$.
5  Search in electron capture decay ${}^{7}\mathrm {Be}$ $\rightarrow$ ${}^{7}\mathrm {Li}$ ${{\mathit \nu}_{{{x}}}}$. Kinematic threshold is $\sim{}$850 keV.
6  Search for ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$. Assumes lifetime of ${{\mathit \nu}_{{{x}}}}$ $>$ 50 ns.
7  Limit from prompt lepton number violating trilepton search.
8  ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ decay through ${{\mathit U}}_{{{\mathit e}} {{\mathit x}}}$. 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.
9  Searches for a Majorana Heavy Neutral Lepton producing a ${{\mathit \pi}^{-}}{{\mathit e}^{+}}$ resonance in the same sign dilepton decay ${{\mathit D}}$ $\rightarrow$ ${{\mathit K}}{{\mathit \pi}^{-}}{{\mathit e}^{+}}{{\mathit e}^{+}}$.
10  BRYMAN 2019 sets best limits $\vert U_{ex}\vert ^2$ $<$ $1 \times 10^{-4} - 2 \times 10^{-7}$ in the mass range ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}\sim{}2 - 55$ MeV, respectively, using the precision branching ratio measurement in AGUILAR-AREVALO 2015. See also BRYMAN 2019A.
11  Search for ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$.
12  Search for ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$.
13  PARK 2016 quotes an approximate limit B( ${{\mathit B}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$) $<$ $3 \times 10^{-6}$ in the mass range ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $0.2 - 1.4$ GeV.
14  Search for ${{\mathit B}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$.
15  Search for prompt ${{\mathit \nu}_{{{x}}}}$ decay signatures.
16  Search for displaced ${{\mathit \nu}_{{{x}}}}$ decay signatures.
17  Searches for ${{\mathit K}}$ or ${{\mathit \pi}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \nu}_{{{e}}}}$ using a beam dump experiment at the 70 GeV Serpukhov proton synchrotron. BARANOV 1993 also considers limits for $\vert {{\mathit U}}_{{{\mathit e}} {{\mathit x}}}{{\mathit U}}_{{{\mathit \mu}} {{\mathit x}}}\vert $ from ${{\mathit K}}$ or ${{\mathit \pi}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{{x}}}}$, ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \nu}_{{{e}}}}$.
18  ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ decay through ${{\mathit U}}_{{{\mathit e}} {{\mathit x}}}$.
19  BERNARDI 1988 also considers bounds on $\vert {{\mathit U}}_{{{\mathit e}} {{\mathit x}}}{{\mathit U}}_{{{\mathit \mu}} {{\mathit x}}}\vert $.
20  ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ decay through ${{\mathit U}}_{{{\mathit e}} {{\mathit x}}}$.
21  ${{\mathit D}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\mathit \ell}^{+}}{{\mathit \nu}_{{{{{\mathit \ell}}}}}}$.
22  ${{\mathit D}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\mathit \ell}^{+}}{{\mathit \nu}_{{{{{\mathit \ell}}}}}}$ or ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\mathit \pi}^{+}}$.
References