Stable Neutral Heavy Lepton MASS LIMITS

Note that LEP results in combination with REUSSER 1991 exclude a fourth stable neutrino with $\mathit m<$ 2400 GeV.

Mass $\boldsymbol m$ INSPIRE search

VALUE (GeV) CL% DOCUMENT ID TECN  COMMENT
$\bf{>45.0}$ 95
ABREU
1992B
DLPH Dirac
$\bf{>39.5}$ 95
ABREU
1992B
DLPH Majorana
$>44.1$ 95
ALEXANDER
1991F
OPAL Dirac
$>37.2$ 95
ALEXANDER
1991F
OPAL Majorana
$\text{none 3 - 100}$ 90
SATO
1991
KAM2 Kamiokande II
$>42.8$ 95 1
ADEVA
1990S
L3 Dirac
$>34.8$ 95 1
ADEVA
1990S
L3 Majorana
$>42.7$ 95
DECAMP
1990F
ALEP Dirac
1  ADEVA 1990S limits for the heavy neutrino apply if the mixing with the charged leptons satisfies $\vert \mathit U_{1\mathit j}\vert ^2$ $+$ $\vert \mathit U_{2\mathit j}\vert ^2$ $+$ $\vert \mathit U_{3\mathit j}\vert ^2$ $>$ $6.2 \times 10^{-8}$ at ${\mathit m}_{{{\mathit L}^{0}}}$ = 20 GeV and $>~5.1 \times 10^{-10}$ for ${\mathit m}_{{{\mathit L}^{0}}}$ = 40 GeV.
  References:
ABREU 1992B
PL B274 230 Searches for Heavy Neutrinos from ${{\mathit Z}^{0}}$ Decays
ALEXANDER 1991F
ZPHY C52 175 Measurement of the ${{\mathit Z}^{0}}$ Line Shape Parameters and the Electroweak Couplings of Charged Leptons
SATO 1991
PR D44 2220 Mass Limits for Dark Matter Particles Derived from High Energy Neutrinos from the Sun
ADEVA 1990S
PL B251 321 A Search for Heavy Charged and Neutral Leptons from ${{\mathit Z}^{0}}$ Decays
DECAMP 1990F
PL B236 511 A Search for New Quarks and Leptons from ${{\mathit Z}^{0}}$ Decay