Forward-backward asymmetry ($A_{\mathrm{FB}}=({\sigma }_F-{\sigma }_B)/({\sigma }_F+{\sigma }_B)$)

The normalized difference of forward and backward cross sections relative to a specified incoming-particle axis. For $d\sigma /dc=K[(A+B)(1+c^2)+2(A-B)c]$ with $c=\cos \theta$, integration gives ${\sigma }_F-{\sigma }_B=2K(A-B)$ and ${\sigma }_F+{\sigma }_B=8K(A+B)/3$, hence $A_{\mathrm{FB}}=3(A-B)/(4(A+B))$. The pole forward-backward asymmetry for charged leptons is its specialized Z boson result.