= Wolfenstein parametrization
{c}
{title2=$\lambda,\ A,\ \rho,\ \eta$}
The Wolfenstein parametrization expands the three-generation CKM matrix in its small $1$-$2$ mixing parameter $\lambda=s_{12}$, defining $s_{23}=A\lambda^2$ and $s_{13}e^{i\delta}=A\lambda^3(\rho+i\eta)$. To cubic order its rows are $(1-\lambda^2/2,\lambda,A\lambda^3(\rho-i\eta))$, $(-\lambda,1-\lambda^2/2,A\lambda^2)$, and $(A\lambda^3(1-\rho-i\eta),-A\lambda^2,1)$. Higher orders restore exact unitarity. Rephasing-invariant barred parameters are defined from ratios of CKM entries rather than this truncated expansion.
Back to article page
