[Rivet] WFinder

[David Grellscheid]

Hi all,

to pick up on the discussion last week. I've implemented the absolute
minimal change in the WFinder we wanted for the quick release, before
discussing it again in the longer term:

 replace hardest neutrino with the total missing Et 4-vector

However, even this change kills all validation on the ~20 ish analyses
that use the WFinder, the signal efficiency drops massively.

I'm tempted to deprecate WFinder immediately, leave it as is for one
more release, but mark all analyses using it as UNVALIDATED.

There are also other analyses that explicitly count neutrinos without
using WFinder. Should those be UNVALIDATED, too?

Thanks,

  David