Particles Initial Conditions tab:
a is the separation (in units of Compton’s wavelength) between their CM’s in the x direction
b is the separation (in units of Compton’s wavelength) between their CM’s in the z direction
v1, v2 and v3 are the x, y and z components of the initial velocity of particle 1. Particle 2 moves with initial velocity -v1,-v2 and -v3.
Z1 and Z2 are the initial phases of the two CC’s in their internal motion around their CM’s.
angles theta and phi define the initial orientation of the spin of particle 1.