Relativistic two-body phase space
= Relativistic two-body phase space
{title2=$\frac{d\Phi_2}{d\Omega}=\frac{k}{16\pi^2\sqrt s}$}
For two outgoing particles with centre-of-mass momentum magnitude $k$ and total energy $\sqrt s$, integrating the four-momentum delta function gives $d\Phi_2/d\Omega=k/(16\pi^2\sqrt s)$. A factor $1/2!$ for identical outgoing particles is inserted when counting events over the full phase space, not into this labelled kinematic measure itself.