Differential scattering cross-section ($d\sigma /d\Omega$)

The differential scattering cross-section is the effective incident area scattered per unit solid angle. It is defined by the ratio of the outgoing particle rate through $d\Omega$ to the incident flux.

For an azimuthally symmetric classical scattering map from impact parameter $b$ to scattering angle $\theta$,When several impact parameters produce the same angle, their nonnegative contributions are summed.

Ifthen the ratio of scattered radial probability current through $r^{2}d\Omega$ to the incident probability flux is