Relativistic Differential Cross-section

[math]d\sigma=\frac{1}{F}|\mathcal{M}|^2 dQ[/math]

dQ is the invariant Lorentz phase space factor and F is the flux of incoming particles

[math]dQ=(2π)^4\delta^4(p_1 + p_2 − p_1^' − p_2^')\frac{d^3p_1^'}{(2π)^32E_1^'}\frac{d^3p_2^'}{{(2π)^32E_2^'}[/math]

[math]\frac{d\sigma}{d\Omega}=\frac{1}{64\pi^2 s} \frac{\mathbf p_f}{\mathbf p_i}|\mathcal {M}|^2[/math]