LEPTONS INSPIRE   JSON PDGID:
S035

${{\mathit \tau}}$

$J$ = $1/2$ 
${{\mathit \tau}}$ discovery paper was PERL 1975. ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ cross-section threshold behavior and magnitude are consistent with pointlike spin-${}^{}1/2{}^{}$ Dirac particle. BRANDELIK 1978 ruled out pointlike spin-0 or spin-1 particle. FELDMAN 1978 ruled out $\mathit J = 3/2$. KIRKBY 1979 also ruled out $\mathit J$=integer, $\mathit J = 3/2$.
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${{\mathit \tau}}$ MASS $1776.93$ $\pm0.09$ MeV 
 
(${\mathit m}_{{{\mathit \tau}^{+}}}-{\mathit m}_{{{\mathit \tau}^{-}}})/\mathit m_{{\mathrm {average}}}$ $<2.8$ $\times 10^{-4}$   CL=90%
 
${{\mathit \tau}}$ MEAN LIFE ($2.903$ $\pm0.005$) $ \times 10^{-13}$ s 
 
$({\mathit \tau}_{{{\mathit \tau}^{+}}}-{\mathit \tau}_{{{\mathit \tau}^{-}}})/{\mathit \tau}_{\mathrm {average}}$ $< 7.0$ $\times 10^{-3}$   CL=90%
 
▸  ${{\mathit \tau}}$ MAGNETIC MOMENT ANOMALY
▸  ${{\mathit \tau}}$ ELECTRIC DIPOLE MOMENT ($\mathit d_{{{\mathit \tau}}}$)
▸  ${{\mathit \tau}}$ WEAK DIPOLE MOMENT ($\mathit d{}^{\mathit w}_{{{\mathit \tau}}}$)
▸  ${{\mathit \tau}}$ WEAK ANOMALOUS MAGNETIC DIPOLE MOMENT ($\alpha {}^{\mathit w}_{{{\mathit \tau}}}$)
▸  ($\Gamma\mathrm {({{\mathit \tau}^{+}})}$ $−$ $\Gamma\mathrm {({{\mathit \tau}^{-}})}$) / ($\Gamma\mathrm {({{\mathit \tau}^{+}})}$ + $\Gamma\mathrm {({{\mathit \tau}^{-}})}$)
▸  ${{\mathit \tau}}$-DECAY PARAMETERS
${{\mathit \tau}^{+}}$ modes are charge conjugates of the modes below. ``${{\mathit h}^{\pm}}$'' stands for ${{\mathit \pi}^{\pm}}$ or ${{\mathit K}^{\pm}}$. ``${{\mathit \ell}}$'' stands for ${{\mathit e}}$ or ${{\mathit \mu}}$. ``Neutrals'' stands for ${{\mathit \gamma}}$'s and/or ${{\mathit \pi}^{0}}$'s.
Mode  
Fraction ($\Gamma_i$ / $\Gamma$) Scale Factor/
Conf. Level		 P(MeV/c)  
▸  Modes with one charged particle
▸  Modes with ${{\mathit K}^{0}}$'s
▸  Modes with three charged particles
▸  Modes with five charged particles
▸  Miscellaneous other allowed modes
▸  $\mathit L$ means lepton number Lepton Family number ($\mathit LF$), Lepton number ($\mathit L$), violation ($\mathit e.g.$ ${{\mathit \tau}^{-}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \pi}^{-}}{{\mathit \pi}^{-}}$). or Baryon number ($\mathit B$) violating modes Following common usage, $\mathit LF$ means lepton family violation $\mathit and~not$ lepton number violation ($\mathit e.g.$ ${{\mathit \tau}^{-}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$). $\mathit B$ means baryon number violation.
[1] Basis mode for the ${{\mathit \tau}}$.
[2] See the Particle Listings below for the energy limits used in this measurement.
Constrained Fit information