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:
Γ(M→1+2)=|→p1|32π2M2∫dΩ|M|2=|→p1|8πM2|M|2,
where M is the amplitude of the process, M is the mass of the initial particle and |→p1|=|→p2| 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