Averaging over neutrino species, the invisible ${{\mathit Z}}$ decay width determines the effective neutrino coupling $\mathit g{}^{{{\mathit \nu}_{{{{\mathit \ell}}}}}}$. For $\mathit g{}^{{{\mathit \nu}_{{e}}}}$ and $\mathit g{}^{{{\mathit \nu}_{{\mu}}}}$, ${{\mathit \nu}_{{e}}}{{\mathit e}}$ and ${{\mathit \nu}_{{\mu}}}{{\mathit e}}$ scattering results are combined with $\mathit g{}^{{{\mathit e}}}_{\mathit A}$ and $\mathit g{}^{{{\mathit e}}}_{\mathit V}$ measurements at the ${{\mathit Z}}$ mass to obtain $\mathit g{}^{{{\mathit \nu}_{{e}}}}$ and $\mathit g{}^{{{\mathit \nu}_{{\mu}}}}$ following NOVIKOV 1993C.
From ${{\mathit \nu}_{{\mu}}}{{\mathit e}}$ and ${{\mathit \nu}_{{e}}}{{\mathit e}}$ scattering
1VILAIN 1994 derive this value from their value of $\mathit g{}^{{{\mathit \nu}_{{\mu}}}}$ and their ratio $\mathit g{}^{{{\mathit \nu}_{{e}}}}/\mathit g{}^{{{\mathit \nu}_{{\mu}}}}$ = $1.05$ ${}^{+0.15}_{-0.18}$.
References:
VILAIN
1994
PL B320 203
Flavour Universality of Neutrino Couplings with the ${{\mathit Z}^{0}}$
