Limits on heavy neutral lepton mixing parameters

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

INSPIRE   JSON  (beta) 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
$<0.1$ 95 1
AAD
2024AW
 ATLS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 1 TeV
$<3 \times 10^{-4}$ 95 2
AAD
2024BU
 ATLS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $20 - 50$ GeV
$<4 \times 10^{-6}$ 95 3
HAYRAPETYAN
2024AB
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $20 - 60$ GeV
$<1 \times 10^{-3}$ 95 3
HAYRAPETYAN
2024AB
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}{ {}\gtrsim{} }$ ${\mathit m}_{{{\mathit W}}}$
$<1 \times 10^{-5}$ 95 4
HAYRAPETYAN
2024S
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 2.5 GeV
$<1 \times 10^{-6}$ 95 5
HAYRAPETYAN
2024V
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 10 GeV
$<5 \times 10^{-7}$ 95 6
AAD
2023AO
 ATLS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}\sim{}3 - 15$ GeV, ${{\mathit p}}{{\mathit p}}$ at 13 TeV
$<3 \times 10^{-4}$ 90 7
AGNES
2023A
 DS50 ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $7 - 35$ keV
$<3 \times 10^{-8}$ 90 8
BAROUKI
2022
RVUE Near ${\mathit m}_{{{\mathit D}_{{{s}}}}}–{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<1 \times 10^{-6}$ 95 9
TUMASYAN
2022AD
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}\sim{}8 - 14$ GeV, ${{\mathit p}}{{\mathit p}}$ at 13 TeV
$<2 \times 10^{-4}$ 95 10
FRIEDRICH
2021
Near ${\mathit m}_{\mathrm {{}^{7}\mathrm {Be}}}−$ ${\mathit m}_{\mathrm {{}^{7}\mathrm {Li}}}$ kin. thres.
$<1 \times 10^{-9}$ 90 11
CORTINA-GIL
2020
NA62 ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $150 - 400$ MeV
$<2 \times 10^{-5}$ 95 12
AAD
2019F
 ATLS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $15 - 40$ GeV
$<1 \times 10^{-9}$ 90 13
ABE
2019B
 T2K Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<1 \times 10^{-4}$ 90 14
ABLIKIM
2019AL
 BES3 ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $0.3 - 0.7$ GeV
$<2 \times 10^{-7}$ 90 15
BRYMAN
2019
RVUE ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}\sim{}$ 55 MeV
$<1 \times 10^{-8}$ 90 16
AGUILAR-AREVA..
2018A
 PIEN ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $60 - 120$ MeV
$<3 \times 10^{-7}$ 90 17
CORTINA-GIL
2018
NA62 ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $200 - 400$ MeV
$<1 \times 10^{-6}$ 90 18
PARK
2016
BELL ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 1.4 GeV
$<3 \times 10^{-5}$ 90 19
LIVENTSEV
2013
BELL Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $2 - 2.5$ GeV
$<3 \times 10^{-5}$ 95 20
ABREU
1997I
 DLPH ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $6 - 50$ GeV
$<2 \times 10^{-5}$ 95 21
ABREU
1997I
 DLPH Near ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 3.5 GeV
$<1 \times 10^{-5}$ 90 22
BARANOV
1993
Near ${\mathit m}_{{{\mathit \pi}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<2 \times 10^{-7}$ 90 22
BARANOV
1993
Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<1 \times 10^{-7}$ 23, 24
BERNARDI
1988
CNTR Near ${\mathit m}_{{{\mathit \pi}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<2 \times 10^{-9}$ 25, 24
BERNARDI
1988
CNTR Near ${\mathit m}_{{{\mathit K}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<1 \times 10^{-7}$ 90 26
DORENBOSCH
1986
CHRM Near ${\mathit m}_{{{\mathit D}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
$<1 \times 10^{-7}$ 90 27
COOPER-SARKAR
1985
BEBC Near ${\mathit m}_{{{\mathit D}}}−{\mathit m}_{{{\mathit e}}}$ kin. thres.
• • We do not use the following data for averages, fits, limits, etc. • •
$<2 \times 10^{-5}$ 95 28
SIRUNYAN
2018K
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $20 - 60$ GeV
$<0.01$ 95 28
SIRUNYAN
2018K
 CMS ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}{ {}\gtrsim{} }$ ${\mathit m}_{{{\mathit W}}}$
1  AAD 2024AW search for scattering of same-sign boson pairs into same-sign electron pairs, mediated by a virtual Majorana HNL, in the HNL mass range 50 GeV to 20 TeV. Limits are also set for $\vert V_{{{\mathit e}} {{\mathit x}}}$ V${}^{*}_{{{\mathit \mu}} {{\mathit x}}}\vert $.
2  AAD 2024BU search for same-sign electron pairs in semileptonic decays of top quarks via a Majorana HNL, in the HNL mass range $15 - 75$ GeV.
3  HAYRAPETYAN 2024AB search for ${{\mathit W}}$ $\rightarrow$ ${{\mathit e}}{{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}}{{\mathit e}}{{\mathit \ell}}{{\mathit \nu}_{{{{{\mathit \ell}}}}}}$ 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.
4  HAYRAPETYAN 2024S search for ${{\mathit W}}$ $\rightarrow$ ${{\mathit e}}{{\mathit \nu}_{{{x}}}}$ followed by ${{\mathit \nu}_{{{x}}}}$ displaced decay in flight to electromagnetic and hadronic showers in the CMS muon chamber, in the mass range ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $1 - 3$ 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 ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ 3 GeV.
5  HAYRAPETYAN 2024V searches for ${{\mathit W}}$ $\rightarrow$ ${{\mathit e}}{{\mathit \nu}_{{{x}}}}$ with displaced decay ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}}{{\mathit j}}$, i.e. with one jet, over the range ${\mathit m}_{{{\mathit \nu}_{{{x}}}}}$ $\sim{}$ $2 - 20$ GeV. Limits are set for both Dirac and Majorana HNLs.
6  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.
7  Search for ionization signals in an LArTPC. Assumes the candidate particle is 100$\%$ of dark matter.
8  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.
9  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${}^{-1}$.
10  Search in electron capture decay ${}^{7}\mathrm {Be}$ $\rightarrow$ ${}^{7}\mathrm {Li}$ ${{\mathit \nu}_{{{x}}}}$. Kinematic threshold is $\sim{}$850 keV.
11  Search for ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$. Assumes lifetime of ${{\mathit \nu}_{{{x}}}}$ $>$ 50 ns.
12  Limit from prompt lepton number violating trilepton search.
13  ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, 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.
14  Searches for a Majorana Heavy Neutral Lepton producing a ${{\mathit \pi}^{-}}{{\mathit e}^{+}}$ resonance in the same sign dilepton decay ${{\mathit D}}$ $\rightarrow$ ${{\mathit K}}{{\mathit \pi}^{-}}{{\mathit e}^{+}}{{\mathit e}^{+}}$.
15  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.
16  Search for ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$.
17  Search for ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$.
18  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.
19  Search for ${{\mathit B}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$.
20  Search for prompt ${{\mathit \nu}_{{{x}}}}$ decay signatures.
21  Search for displaced ${{\mathit \nu}_{{{x}}}}$ decay signatures.
22  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 ${{\mathit \pi}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{{x}}}}$, ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \nu}_{{{e}}}}$.
23  ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ decay through ${{\mathit U}}_{{{\mathit e}} {{\mathit x}}}$.
24  BERNARDI 1988 also considers bounds on $\vert {{\mathit U}}_{{{\mathit e}} {{\mathit x}}}{{\mathit U}}_{{{\mathit \mu}} {{\mathit x}}}\vert $.
25  ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ decay through ${{\mathit U}}_{{{\mathit e}} {{\mathit x}}}$.
26  ${{\mathit D}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\mathit \ell}^{+}}{{\mathit \nu}_{{{{{\mathit \ell}}}}}}$.
27  ${{\mathit D}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}_{{{x}}}}$, with ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\mathit \ell}^{+}}{{\mathit \nu}_{{{{{\mathit \ell}}}}}}$ or ${{\mathit \nu}_{{{x}}}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\mathit \pi}^{+}}$.
28  Superseded by HAYRAPETYAN 2024AB.
References