Necessary angles for Wigner rotations

[KaiHabermann]

Right now the wigner_angles method of the LorentzTrafo class will return the three angles needed to rotate in the rest frame, before the boost. They are named phi_rf, theta_rf, psi_rf. Here only theta_rf is used in analyses. Maybe it would make sense to return only theta_rf.

This can be seen in the tests agains DPD for the roations between the different final state particle frames and the helicity angles

[mmikhasenko]

One would see that need of all three angles, once consider 4 body decays. You might want to add a test for it.

I think even for 3 body the angles phi_rf, and psi_rfcome non-zero, if the initial configuration is not aligned for zx plane. To be checked.

[KaiHabermann]

Okay. I will alter it, so that all three angles are returned. Maybe even as a named tuple. Then it is a little clearer for people which is which

[mmikhasenko]

Either fine, the angles do not have clear standard name. usually, phi, theta, psi, or phi, theta, gamma, or alpha, beta, gamma.

[KaiHabermann]

Cool. I will go named then. I prefer thus and as long as we clearly document the naming scheme it should make using the application easier