Improve handling of phase-space generation for cases of decays having e+e- pair to make RareLbToLll model.
- Improve handling of phase-space generation for cases of decays having e+e- pair to make RareLbToLll model useable.
- Some code modernization of RareLbToLll to make things const where they are constant and pass const references instead of raw pointers in most places.
Test Plan: Tested locally that nothing changes for Lz mu mu final state. In case of Lb --> Lz e+ e-, without this change model is effectively unuseable as maximum probability gets too high and accept-reject fails to find working configuration in 1000 trials. After change code can generate 1M events without any issue and gives expected q2 distribution. I'm not adding test as I will do this directly to new framework.
Reviewers: tlatham, jback
Reviewed By: tlatham, jback
Differential Revision: https://phab.hepforge.org/D84