[Rivet] Truth jets and Rivet

[Karl Gellerstedt]

Hi Andy and Chris,

Thank you very much for your detailed answers! I’ll dig into the Rivet details right away.

Cheers,
Karl

> On 25 Jan 2017, at 19:43, Christian Gutschow <chris.g at cern.ch> wrote:
> 
> Hi,
> 
> just to add:
> 
>>> Do you know if pile-up jets are included in the xAOD truth jet
>>> collections, (AntiKt4TruthJets/TruthWZJets)?
>> 
>> I should know this, but my mind has gone fuzzy and I can't remember how much is retained. My suspicion is that they are not there, and that a dedicated collection for truth pile-up jets is used: pile-up is simulated in separate simulation jobs and combined at the digitization stage. Zach Marshall or John Chapman would know, I'm sure. Try asking on the PMG mailing list?
>> 
>> Also, the truth pile-up jet info is heavily thinned before xAOD, so at most you'd get the truth-jet filters but no particle constituent info. Note that truth-jet clustering is done independently for the signal event and each pile-up event, so it's perfectly possible for signal and pile-up jets to completely overlap without "taking bites" out of each other.
> 
> There is no pileup in the truth collections and no pileup jets in these truth jet collections either.
> 
>> 
>>> I’ve also had a look at Rivet (a really impressive work!), and do you
>>> know what setup to use for the FastJet projection, to get jets
>>> similar to the “AntiKtTruthWZJets”?
>> 
>> Good question. I think the W/Z jets can't be exactly replicated in Rivet because they explicitly look for a W or Z parent: we avoid that. But I think you would get a very similar answer if you configured normal akT jets with the correct radius and pT threshold, and also configure the DressedLeptons projection to find prompt electrons and muons: then veto any jets where they overlap. Maybe with a narrower veto radius than the jet radius.
>> 
>> Off the top of my head, something like this would work:
>> 
>> // Init
>> FinalState photons(Cuts::abspid == PID::PHOTON);
>> PromptFinalState leptons(Cuts::abspid == PID::ELECTRON || Cuts::abspid == PID::MUON);
>> declare(DressedLeptons(leptons, photons, Cuts::pT > 15*GeV), "Leptons");
>> 
>> // Analyze
>> const Particles leptons = apply<FinalState>(event, "Leptons").particles();
>> Jets jets = apply<FinalState>(event, "Jets").jets(Cuts::pT > 20*GeV);
>> for (const Particle& l : leptons)
>>  ifilter_reject(jets, deltaRLess(l, 0.3));
>> 
>> There are other ways that could also work, such as passing the FastJets projection a VetoedFinalState for clustering, where the veto is on anything selected by the DressedLeptons projection. Maybe that would be closer to the WZJets definition.
> 
> I think you have to be a little bit careful what version you’re comparing because the xAOD TruthWZJet collection used to exclude neutrinos (until about six months ago if I remember correctly). 
> 
> I played around with this some time ago and remember the 2nd option with the VetoedFinalState being indeed closer to the TruthWZJets collection.
> 
> Cheers,
> Chris
> 
> 
>  —
> 
>  Dr. Christian Gütschow
> 
>  Department of Physics and Astronomy
>  University College London
>  Gower Street
>  London WC1E 6BT
> 
>  > D10 Physics Building
>  > +44 (0)20 7679 3775
>  > chris.g at cern.ch <mailto:chris.g at cern.ch>
> 
> 
> 

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