Beam spectra don't work for process groups

[Frank Siegert]

Beam spectra like EPA are broken for process groups. The reason is that the beam weight is calculated at a scale Q² which is determined by the process's scale setter (cf. Phase_Space_Handler.C:298). Process groups don't have their own scale setter though, but only their contained single processes, because some of our scale setters (QCD, *METS) are flavour specific (in what they are allowed to combine in the clustering).

Before looking for a technical solution, I have a conceptual question though: Should the beam spectrum weight really be calculated at the factorisation scale, or should this be implemented completely different?

Assuming we really want it at the factorisation scale, then we could:

• Quick hack: Give Process_Group a scale setter but then the user can't use any scale setter which is flavour specific. Unfortunately our default and probably most useful one is METS.
• Proper Solution: Move the beam weight calculation into the Single_Process::Differential like we do for the ISR weight.

[Frank Siegert]

I've implemented the second solution in r14836. It needs more thorough testing before I'll mark this bug as resolved.

[Stefan Hoeche]

Milestone old deleted