= Neutrino neutral-to-charged current ratio
{title2=$R_\nu=\sigma_{\rm NC}^{\nu N}/\sigma_{\rm CC}^{\nu N}$}
For an isoscalar valence target and <massless particle>[massless] leading-order scattering, $R_\nu=G_L^2+G_R^2/3$, where $G_{L/R}^2=(g_{L/R}^u)^2+(g_{L/R}^d)^2$. The factor $1/3$ is $\int_0^1(1-y)^2dy$. With Standard Model <quark> couplings and $w=\sin^2\theta_W$, this becomes $1/2-w+20w^2/27$. Sea <quarks> and threshold, nuclear and <Quantum chromodynamics>[QCD] corrections matter beyond this limit.
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