Equal-energy two-photon decay of a moving particle
= Equal-energy two-photon decay of a moving particle
For a parent moving at $\beta c$ and decaying into two <photons> of equal laboratory energies, <momentum conservation> gives <photon> directions symmetric about the parent direction with $\cos\theta=\beta$. The opening <angle> is $2\arccos\beta$. In the parent <rest frame> the <photons> are opposite and perpendicular to the boost direction.