Tau single-tag and double-tag normalization
= Tau single-tag and double-tag normalization
For $N$ tau-pair events and a tag mode with <branching fraction> $B$, the tagged-hemisphere count is $S=2NB\epsilon$ and the double-tag event count is $D=NB^2\epsilon_{ii}$. Eliminating $B$ gives $N=S^2\epsilon_{ii}/(4D\epsilon^2)$. Efficiency correlations matter: $\epsilon_{ii}$ need not equal $\epsilon^2$. An inclusive branching-fraction fit must include unlisted decay categories.