Since the 4-momentum must be conserved, there is no angular dependence in a 2-body decay in the CM frame. But If you are asking yourself what is the phase-space of such process, you should take a look at equation 4.72 of the book I mentioned in the comments:

$$\Gamma(M\to 1 + 2)=\dfrac{|\vec{p_1}|}{32 \pi^2 M^2} \int \mathrm{d}\Omega |\mathcal{M}|^2=\dfrac{|\vec{p_1}|}{8 \pi M^2}|\mathcal{M}|^2,$$

where $\mathcal{M}$ is the amplitude of the process, $M$ is the mass of the initial particle and $|\vec{p_1}|=|\vec{p_2}|$ is the final 3-momentum of one of the particles.

This post imported from StackExchange Physics at 2014-04-14 17:03 (UCT), posted by SE-user JSchwinger