[Rivet] undocumented behaviour in wfinder/zfinder (bug ?)

[Nicolas Morange]

Hello Frank,

I've read the new code, and it seems correct to me. Thanks !
Maybe one little thing (I don't understand fully how projections work): is it 
normal that line 124 of ZFinder.cc is commented ?

I was able to discover this bug because I'm studying Z+b, where the other 
leptons in the event play a much more important role than in Z+jets, because 
of the semi-leptonic decays. The overall effect was ~3% on the inclusive 
cross-section.

Cheers,
Nicolas


Le Mardi 2 Août 2011 12:12:06 Frank Siegert a écrit :
> Hi Nicolas,
> 
> I have revamped the implementation of [WZ]Finder to correctly exclude
> particles from the RemainingFinalState:
> 
>    http://projects.hepforge.org/rivet/trac/changeset/3268
> 
> IMO it's much easier to read now, so maybe you could take another look
> and check whether you see any remaining inconsistency. You can browse
> that revision at
> 
>    http://projects.hepforge.org/rivet/trac/browser/trunk?rev=3268
> 
> The idea now is that the WFinder and ZFinder are FinalState projections
> which have the original constituents as _theParticles and the W or Z as
> _bosons. This makes it easier to exclude the original particles from the
> remaining final state while still allowing for re-using the existing
> projections (one of which, LeptonClusters, is also much simpler now).
> 
> These changes don't seem to have a large effect, but they do have an
> effect (very small) of increasing jet multiplicity, as would be expected
> since we include more particles in the jets now:
> 
> http://fsiegert.web.cern.ch/fsiegert/tmp/wzfinder
> 
> This will be released very soon as Rivet 1.6.0.
> 
> Best,
> Frank
> 
> On 29/07/11 19:54, Nicolas Morange wrote:
> > Hi Frank,
> > 
> > Thanks for your quick answer.
> > For what I see all the other leptons are removed, for
> > LeptonClustersConstituents (which contains the particles that will
> > eventually be removed) doesn't know about pT and eta cuts. That seems
> > normal, as only the clustered leptons have to pass the cuts.
> > 
> > As a quick&dirty workaround I'm trying to merge :
> > zfinder.remainingFinalState()
> > + zfinder.getProjection<FinalState>("LeptonClusters")
> > - zfinder.constituentsFinalState()
> > which adds the composite clustered leptons to the final state.
> > that's not completely correct but that should do a decent job.
> > 
> > Cheers,
> > Nicolas
> > 
> > Le Vendredi 29 Juillet 2011 19:30:41 Frank Siegert a écrit :
> >> Hi Nicolas,
> >> 
> >> I'm afraid you are right, there is an inconsistency. It is not
> >> removing
> >> all leptons though, but "only" the ones which pass the initial lepton
> >> cuts. But that's still more than the ones used as Z, and thus wrong.
> >> 
> >> It's not obvious to me how to solve this with the current approach of
> >> chaining existing projections (LeptonClusters and InvMassFinalState in
> >> this case). I would need to be able to access the original particles
> >> which form the two LeptonClusters accepted by IMFS. So there doesn't
> >> seem to be a way around duplicating LC and IMFS into a combined
> >> projection, which might as well be the ZFinder then.
> >> 
> >> I'll think about this for an hour and if I (or anybody else on this
> >> list) haven't come up with a better solution by then, I'll start
> >> working
> >> on it.
> >> 
> >> Cheers,
> >> Frank
> >> 
> >> On 29/07/11 16:46, Andy Buckley wrote:
> >>> Hi Nicholas,
> >>> 
> >>> I'm a bit uncertain about exactly how the remainingFS works for
> >>> WFinder
> >>> and ZFinder... hopefully someone can clarify and check that there is
> >>> no
> >>> bug: Frank S, can you help?
> >>> 
> >>> We're just about to make a new Rivet release, and I just uploaded
> >>> the
> >>> release tarballs to the HepForge downloads area... but I'll wait for
> >>> confirmation that there's not a bug before making the release
> >>> official.
> >>> 
> >>> Cheers,
> >>> Andy
> >>> 
> >>> On 29/07/11 15:29, Nicolas Morange wrote:
> >>>> Hello,
> >>>> 
> >>>> I'm writing a Z+jets analysis.
> >>>> Thus I use a ZFinder whose remainingFinalState() is chained to a
> >>>> FastJet. However, the code in ZFinder
> >>>> 
> >>>> 00044 LeptonClusters leptons(fs, bareleptons, dRmax,
> >>>> 00045 clusterPhotons, excludePhotonsFromRFS,
> >>>> 00046 etaRanges, pTmin);
> >>>> 00047 addProjection(leptons, "LeptonClusters");
> >>>> 00048 InvMassFinalState imfs(leptons, std::make_pair(pid, -pid),
> >>>> m2_min,
> >>>> m2_max);
> >>>> 00049 addProjection(imfs, "IMFS");
> >>>> 00050
> >>>> 00051 VetoedFinalState remainingFS;
> >>>> 00052
> >>>> remainingFS.addVetoOnThisFinalState(leptons.constituentsFinalState
> >>>> ());
> >>>> 00053 addProjection(remainingFS, "RFS");
> >>>> 
> >>>> gives me the impression that not only the Z leptons are removed
> >>>> from
> >>>> the
> >>>> remainingFS, but also the other leptons in the event.
> >>>> Is this correct ?
> >>>> And how should I do to remove only the Z leptons (and associated
> >>>> photons) from
> >>>> the final state ?
> >>>> 
> >>>> Cheers,
> >>>> Nicolas
> >>>> _______________________________________________
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> >>>> Rivet at projects.hepforge.org
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