[Rivet] Question concering PromptFinalState projection

[Christian Gutschow]

Hi,

the Rivet routines work perfectly fine with the Herwig shower (!) — it’s just Fortran Herwig that doesn’t comply with the HepMC standard, for which the routines might not work. All the more reason to move to the modern incarnations of Herwig...

Cheers,
Chris

On 25 Jan 2017, at 17:31, Dominic Hirschbuehl <dhirsch at mail.cern.ch<mailto:dhirsch at mail.cern.ch>> wrote:

Hi Andy,

thanks a lot for the quick answer.
It is indeed Fortran Herwig and I ran over a MC12 sample. Maybe the
rewriter was not used for this sample.

However, does this mean, that we need to put some disclaimer to our
Rivet routines, that they don't work for the Herwig shower, since
everybody outside ATLAS won't have the rewriter, right?

Cheers
 Dominic

On Wed, Jan 25, 2017 at 05:24:21PM +0000, Andy Buckley wrote:
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
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 Dr. Christian Gütschow

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