# Searches for Decays of Massive ${{\boldsymbol \nu}}$ INSPIRE search

Limits on $\vert \mathit U_{{{\mathit e}}\mathit x}\vert ^2$ as function of ${\mathit m}_{{{\mathit \nu}_{{x}}}}$
VALUE CL% DOCUMENT ID TECN  COMMENT
• • • We do not use the following data for averages, fits, limits, etc. • • •
$<1.6 \times 10^{-4}$ 90 1
 2003 A
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ = 4 MeV
$<4.5 \times 10^{-5}$ 90 1
 2003 A
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ = 7 MeV
$<3.8 \times 10^{-5}$ 90 1
 2003 A
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ = 10 MeV
$<1.5 \times 10^{-3}$ 95
 2001
L3 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=80 GeV
$<0.02$ 95
 2001
L3 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=175 GeV
$<0.3$ 95
 2001
L3 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=200 GeV
$<4 \times 10^{-3}$ 95
 1999 K
L3 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=80 GeV
$<0.05$ 95
 1999 K
L3 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$= 175 GeV
$<2 \times 10^{-5}$ 95 2
 1997 I
DLPH ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=6 GeV
$<3 \times 10^{-5}$ 95 2
 1997 I
DLPH ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=50 GeV
$<1.8 \times 10^{-3}$ 90 3
 1995
MWPC ${\mathit m}_{{{\mathit \nu}_{{h}}}}$ = $1.5$ MeV
$<2.5 \times 10^{-4}$ 90 3
 1995
MWPC ${\mathit m}_{{{\mathit \nu}_{{h}}}}$ = 4 MeV
$<4.2 \times 10^{-3}$ 90 3
 1995
MWPC ${\mathit m}_{{{\mathit \nu}_{{h}}}}$ = 9 MeV
$<1 \times 10^{-5}$ 90 4
 1993
${\mathit m}_{{{\mathit \nu}_{{x}}}}$=100 MeV
$<1 \times 10^{-6}$ 90 4
 1993
${\mathit m}_{{{\mathit \nu}_{{x}}}}$= 200 MeV
$<3 \times 10^{-7}$ 90 4
 1993
${\mathit m}_{{{\mathit \nu}_{{x}}}}$= 300 MeV
$<2 \times 10^{-7}$ 90 4
 1993
${\mathit m}_{{{\mathit \nu}_{{x}}}}$=400 MeV
$<6.2 \times 10^{-8}$ 95
 1990 S
L3 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=20 GeV
$<5.1 \times 10^{-10}$ 95
 1990 S
L3 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=40 GeV
$\text{all values ruled out}$ 95 5
 1990
MRK2 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$ $<$ $19.6$ GeV
$<1 \times 10^{-10}$ 95 5
 1990
MRK2 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$= $22$ GeV
$<1 \times 10^{-11}$ 95 5
 1990
MRK2 ${\mathit m}_{{{\mathit \nu}_{{x}}}}$= $41$ GeV
$\text{all values ruled out}$ 95
 1990 F
ALEP ${\mathit m}_{{{\mathit \nu}_{{x}}}}$= $25.0-42.7$ GeV
$<1 \times 10^{-13}$ 95
 1990 F
ALEP ${\mathit m}_{{{\mathit \nu}_{{x}}}}$= $42.7-45.7$ GeV
$<5 \times 10^{-3}$ 90
 1988
HRS ${\mathit m}_{{{\mathit \nu}_{{x}}}}=1.8$ GeV
$<2 \times 10^{-5}$ 90
 1988
HRS ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=4 GeV
$<3 \times 10^{-6}$ 90
 1988
HRS ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=6 GeV
$<1.2 \times 10^{-7}$ 90
 1988
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=100 MeV
$<1 \times 10^{-8}$ 90
 1988
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=200 MeV
$<2.4 \times 10^{-9}$ 90
 1988
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=300 MeV
$<2.1 \times 10^{-9}$ 90
 1988
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=400 MeV
$<0.02$ 68 6
 1987
${\mathit m}_{{{\mathit \nu}_{{x}}}}=1.5$ MeV
$<8 \times 10^{-4}$ 68 6
 1987
${\mathit m}_{{{\mathit \nu}_{{x}}}}=4.0$ MeV
$<8 \times 10^{-3}$ 90
 1986
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=400 MeV
$<8 \times 10^{-5}$ 90
 1986
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}=1.7$ GeV
$<8 \times 10^{-8}$ 90
 1986
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=100 MeV
$<4 \times 10^{-8}$ 90
 1986
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=200 MeV
$<6 \times 10^{-9}$ 90
 1986
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=400 MeV
$<3 \times 10^{-5}$ 90
 1986
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=150 MeV
$<1 \times 10^{-6}$ 90
 1986
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=500 MeV
$<1 \times 10^{-7}$ 90
 1986
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}=1.6$ GeV
$<7 \times 10^{-7}$ 90 7
 1985
HLBC ${\mathit m}_{{{\mathit \nu}_{{x}}}}=0.4$ GeV
$<8 \times 10^{-8}$ 90 7
 1985
HLBC ${\mathit m}_{{{\mathit \nu}_{{x}}}}=1.5$ GeV
$<0.01$ 90 8
 1983 B
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=10 MeV
$<1 \times 10^{-5}$ 90 8
 1983 B
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=110 MeV
$<6 \times 10^{-7}$ 90 8
 1983 B
CNTR ${\mathit m}_{{{\mathit \nu}_{{x}}}}$=410 MeV
$<1 \times 10^{-5}$ 90
 1983
${\mathit m}_{{{\mathit \nu}_{{x}}}}$=160 MeV
$<1 \times 10^{-6}$ 90
 1983
${\mathit m}_{{{\mathit \nu}_{{x}}}}$=480 MeV
1  BACK 2003A searched for heavy neutrinos emitted from ${}^{8}\mathrm {B}$ decay in the Sun using the decay ${{\mathit \nu}_{{h}}}$ $\rightarrow$ ${{\mathit \nu}_{{e}}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ in the Counting Test Facility (the prototype of the Borexino detector) and obtained limits on heavy neutrino admixture for the ${{\mathit \nu}_{{h}}}$ mass range $1.1 - 12$ MeV.
2  ABREU 1997I long-lived ${{\mathit \nu}_{{x}}}$ analysis. Short-lived analysis extends limit to lower masses with decreasing sensitivity except at $3.5$ GeV, where the limit is the same as at 6 GeV.
3  HAGNER 1995 obtain limits on heavy neutrino admixture from the decay ${{\mathit \nu}_{{h}}}$ $\rightarrow$ ${{\mathit \nu}_{{e}}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ at a nuclear reactor for the ${{\mathit \nu}_{{h}}}$ mass range $2 - 9$ MeV.
4  BARANOV 1993 is a search for neutrino decays into ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \nu}_{{e}}}$ using a beam dump experiment at the 70 GeV Serpukhov proton synchrotron. The limits are not as good as those achieved earlier by BERGSMA 1983 and BERNARDI 1986 , BERNARDI 1988 .
5  BURCHAT 1990 includes the analyses reported in JUNG 1990 , ABRAMS 1989C, and WENDT 1987 .
6  OBERAUER 1987 bounds from search for ${{\mathit \nu}}$ $\rightarrow$ ${{\mathit \nu}^{\,'}}{{\mathit e}}{{\mathit e}}$ decay mode using reactor (anti)neutrinos.
7  COOPER-SARKAR 1985 also give limits based on model-dependent assumptions for ${{\mathit \nu}_{{\tau}}}$ flux. We do not list these. Note that for this bound to be nontrivial, $\mathit x$ is not equal to 3, i.e. ${{\mathit \nu}_{{x}}}$ cannot be the dominant mass eigenstate in ${{\mathit \nu}_{{\tau}}}$ since ${\mathit m}_{{{\mathit \nu}_{{3}}}}$ $<$70 MeV (ALBRECHT 1985I). Also, of course, $\mathit x$ is not equal to 1 or 2, so a fourth generation would be required for this bound to be nontrivial.
8  BERGSMA 1983B also quote limits on $\vert \mathit U_{{{\mathit e}}3}\vert {}^{2}$ where the index 3 refers to the mass eigenstate dominantly coupled to the ${{\mathit \tau}}$. Those limits were based on assumptions about the ${{\mathit D}_{{s}}}$ mass and ${{\mathit D}_{{s}}}$ $\rightarrow$ ${{\mathit \tau}}{{\mathit \nu}_{{\tau}}}$ branching ratio which are no longer valid. See COOPER-SARKAR 1985 .
References:
 BACK 2003A
JETPL 78 261 New Experimental Limits on Heavy Neutrino Mixing in ${}^{8}\mathrm {B}$ Decay Obtained with the Borexino Counting Test Facility
 ACHARD 2001
PL B517 67 Search for Heavy Isosinglet Neutrino in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilation at LEP
 ACCIARRI 1999K
PL B461 397 Search for Heavy Isosinglet Neutrinos in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilation at 130 $<$ $\sqrt {s }$ $<$ 189 GeV
 ABREU 1997I
ZPHY C74 57 Search for Neutral Heavy Leptons Produced in ${{\mathit Z}}$ Decays
 HAGNER 1995
PR D52 1343 Experimental Search for the Neutrino Decay ${{\mathit \nu}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ and Limits on Neutrino Mixing
 BARANOV 1993
PL B302 336 Search for Heavy Neutrinos at the IHEP-JINR Neutrino Detector
PL B251 321 A Search for Heavy Charged and Neutral Leptons from ${{\mathit Z}^{0}}$ Decays
 BURCHAT 1990
PR D41 3542 A Search for Decays of the ${{\mathit Z}^{0}}$ to Unstable Neutral Leptons with Mass between 2.5 and 22 GeV
 DECAMP 1990F
PL B236 511 A Search for New Quarks and Leptons from ${{\mathit Z}^{0}}$ Decay
 AKERLOF 1988
PR D37 577 Experimental Limits on Massive Neutrinos from ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilation at 29 GeV
 BERNARDI 1988
PL B203 332 Further Limit on Heavy Neutrino Coupling
 OBERAUER 1987
PL B198 113 Experimental Limits on the Decay of Reactor Neutrinos
ZPHY C31 21 Mass and Lifetime Limits on New Longlived Particles in 300 ${\mathrm {GeV/}}\mathit c$ ${{\mathit \pi}^{-}}$ Interactions
PL 166B 473 A Search for Decays of Heavy Neutrinos in the Mass Range of 0.5 $−$ 2.8 GeV
PL 122B 465 Experimental Study of the Reaction ${{\mathit \nu}_{{\mu}}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \mu}^{-}}{{\mathit \nu}_{{e}}}$