[Rivet] Question concering PromptFinalState projection

[Andy Buckley]

Hi Dominic,

Is this *Fortran* Herwig?

Indeed it uses non-standard status codes, so Rivet's algorithms will 
break. But in ATLAS we added a Herwig status rewriter, to make it 
compliant -- is that not being used in your sample?

The restriction to look at status 2 only (because status 1 can't be an 
ancestor) is maybe a bit extreme: we could also allow status codes > 10 
to be used (the MC range if I remember correctly). But then we wouldn't 
know what sort of generator-dependence we'd be introducing: for example 
Herwig++ uses status 11 for everything that isn't 1, 2, or 4 so we could 
end up walking up precisely the sort of unphysical debug trees that the 
code is trying to avoid...

Short answer: the generator needs to be compliant with the HepMC status 
scheme. But I thought we had already modified FHerwig in that way.

Andy


On 25/01/17 16:55, Dominic Hirschbuehl wrote:
> Dear all,
>
> I have a question concerning the PromptFinalState projection.
> I did a study on acceptences of lep+jets ttbar events, where I found an
> unexpected differences between Powheg+Pythia6 and Powheg+Herwig samples.
> The differences occured already on the level of the lepton acceptance,
> which includes a dilepton veto.
>
> After some investigation I have the suspicion, that leptons from hadron
> decays are counted as prompt leptons.
>
> Looking to the actual implementation of isPrompt I found this line of code:
> if (ancestor->status() != 2) continue; // no non-standard statuses or
> beams to be used in decision making
>
> Is there a reason to restrict the status codes to 2?
> If I print out all ancestors of a "prompt lepton" from a Herwig showered event
> I get:
>
>     pdg = 2212 status = 101 0 1
>     pdg = 2212 status = 102 0 1
>     pdg = 21 status = 121 1 0
>     pdg = 21 status = 122 1 0
>     pdg = 6 status = 123 1 0
>     pdg = 6 status = 143 1 0
>     pdg = 6 status = 3 1 0
>     pdg = 6 status = 155 1 0
>     pdg = 24 status = 123 0 0
>     pdg = 24 status = 3 0 0
>     pdg = 24 status = 155 0 0
>     pdg = 4 status = 124 1 0
>     pdg = 4 status = 144 1 0
>     pdg = 4 status = 2 1 0
>     pdg = 21 status = 2 1 0
>     pdg = 4 status = 158 1 0
>     pdg = -2 status = 158 1 0
>     pdg = 91 status = 183 0 0
>     pdg = 411 status = 197 0 1
>
> which would indicate that the identified lepton actually comes fomr a
> hadron.
>
> Do I miss something?
>
> Thanks in advance
>   Dominic
>
>
>
>
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-- 
Dr Andy Buckley, Lecturer / Royal Society University Research Fellow
Particle Physics Expt Group, University of Glasgow