[Rivet] MC_HJETS and MC_HINC using ZFinder

[Frank Siegert]

>> I think Julia has a point, namely that additionally to the mass range
>> we can specify a mass target, which means that only the pair closest
>> to the target is being kept. At least in the Higgs analyses this
>> should be changed:
>> - to 0 such that all possible pairs are kept for the user to decide, or
>> - to 125 such that the correct pair is kept
>>
>> Maybe we want to change this to 0 in general? I just don't know
>> whether there are any analyses that rely on it being 91 at the moment,
>> but we could simply set it explicitly to 91 in all existing analyses
>> using the ZFinder such as to remain backward compatible.
>
> This would be a possibility, but it *is* a ZFinder. If we think that
> selecting the Z candidate closest to the known Z mass is reasonable in
> all the existing analyses using ZFinder then I think we should keep it
> there.
>
> Seems to me that the main point is to change the range to one centred on
> 125*GeV in these MC_H* analyses, and to also explicitly set the mass
> target either to 125 or to 0 in them. This use of ZFinder is the
> exception, rather than a reason to change the default, IMHO.

One could also argue that a good default for the ZFinder is to return
all allowed combinations within the given mass range. So the user
would then decide how to pick one and discard the other, or (more
likely) completely discard the rare events where there are two Z's. I
would think that the latter is something more commonly (and easily)
implemented in experimental analyses?

Cheers,
Frank