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

[Frank Siegert]

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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