pdgLive

Heavy Neutral Lepton MASS LIMITS

INSPIRE JSON (beta) PDGID:

Limits apply only to heavy lepton type given in comment at right of data Listings.

See the “Quark and Lepton Compositeness, Searches for” Listings for limits on radiatively decaying excited neutral leptons, $\mathit i.e.$ ${{\mathit \nu}^{*}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit \gamma}}$.

VALUE (GeV)

CL%

DOCUMENT ID

TECN

COMMENT

$\bf{>101.3}$

95

L3

Dirac coupling to ${{\mathit e}}$

$\bf{>101.5}$

95

L3

Dirac coupling to ${{\mathit \mu}}$

$\bf{>90.3}$

95

L3

Dirac coupling to ${{\mathit \tau}}$

$\bf{>89.5}$

95

L3

Majorana coupling to ${{\mathit e}}$

$\bf{>90.7}$

95

L3

Majorana coupling to ${{\mathit \mu}}$

$\bf{>80.5}$

95

L3

Majorana coupling to ${{\mathit \tau}}$

• • We do not use the following data for averages, fits, limits, etc. • •

$>76.0$

95

OPAL

Majorana, coupling to ${{\mathit e}}$

$>88.0$

95

OPAL

Dirac, coupling to ${{\mathit e}}$

$>76.0$

95

OPAL

Majorana, coupling to ${{\mathit \mu}}$

$>88.1$

95

OPAL

Dirac, coupling to ${{\mathit \mu}}$

$>53.8$

95

OPAL

Majorana, coupling to ${{\mathit \tau}}$

$>71.1$

95

OPAL

Dirac, coupling to ${{\mathit \tau}}$

$>76.5$

95

DLPH

Dirac coupling to ${{\mathit e}}$

$>79.5$

95

DLPH

Dirac coupling to ${{\mathit \mu}}$

$>60.5$

95

DLPH

Dirac coupling to ${{\mathit \tau}}$

$>63$

95

ALEP

Dirac

$>54.3$

95

ALEP

Majorana

¹	BUSKULIC 1996S requires the decay length of the heavy lepton to be $<1~$cm, limiting the square of the mixing angle $\vert \mathit U_{{{\mathit \ell}} {{\mathit j}}}\vert ^2$ to $10^{-10}$.

²	BUSKULIC 1996S limit for mixing with ${{\mathit \tau}}$. Mass is $>63.6$ GeV for mixing with ${{\mathit e}}$ or ${{\mathit \mu}}$.

³	BUSKULIC 1996S limit for mixing with ${{\mathit \tau}}$. Mass is $>55.2$ GeV for mixing with ${{\mathit e}}$ or ${{\mathit \mu}}$.

Except where otherwise noted, content of the 2025 Review of Particle Physics is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license. The publication of the Review of Particle Physics is supported by US DOE, MEXT (Japan), INFN (Italy) and CERN. Individual collaborators receive support for their PDG activities from their respective institutes or funding agencies. © 2025. See LBNL disclaimers.