LEPTONS
 INSPIRE search

${{\boldsymbol \tau}}$ $J$ = $1/2$ 

${{\mathit \tau}}$ 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, $\mathit J = 3/2$.
See related reviews:
${{\mathit \tau}}$ Branching Fractions
${{\mathit \tau}}$-Lepton Decay Parameters
${{\mathit \tau}}$ MASS   $1776.86 \pm0.12$ MeV 
(${\mathit m}_{{{\mathit \tau}^{+}}}–{\mathit m}_{{{\mathit \tau}^{-}}})/\mathit m_{{\mathrm {average}}}$   $<2.8 \times 10^{-4}$   CL=90.0%
${{\mathit \tau}}$ 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=90.0%
${{\boldsymbol \tau}}$ MAGNETIC MOMENT ANOMALY
${{\mathit \mu}_{{\tau}}}/({{\mathit e}}\hbar{}/2{{\mathit m}_{{\tau}}})−$1 = (${{\mathit g}_{{\tau}}}−$2)/2   $\text{>-0.052 and <0.013}$   CL=95.0%
${{\mathit \tau}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit K}_S^0}$ ${{\mathit \nu}_{{\tau}}}$ (RATE DIFFERENCE) $/$ (RATE SUM)   $-0.0036 \pm0.0025$  
${{\mathit \tau}^{+}}$ 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.
    constrained fit information