[Rivet] FinalState, FastJets

Andy Buckley andy.buckley at ed.ac.uk
Thu Apr 19 18:45:09 BST 2012

On 19/04/2012 14:04, Andrea Neusiedl wrote:
> Hi,
> I would be greatful for your help. I have some specific Rivet questions
> that is why I chosen this forum.
> First of all, I would like to know if it possible to create different
> "jet collections" in Rivet at run time.
> I would like to have antikt R=0.4 and R=0.6 and differently defined jets
> in context of UseInvisibles.

Hi Andrea,

Yes, you can have multiple different jet projections with different algs 
and parameters: just register (addProjection(...)) each FastJets 
projection with a different name.

> Furthermore,
> I would like to know the definition of
> const FinalState fs(-2.5,2.5);
> addProjection(fs,"OpenFS");
> and
> const FinalState fs(-2.5,2.5);
> addProjection(fs,"FS");
> because in version 1.4.0 I receive the output that in case of "FS"
> projection neutrinos are vetoed. Is this the default?

Hmm, the first one worries me a bit, because we internally use the name 
"OpenFS" to define an internal base final state projection with no phase 
space cuts. I fear that you might be overwriting that, and then the rest 
of the FSes would be messed up. I should check that this isn't possible...

> At last, UseInvisibles would tell FastJet to include neutrinos and
> muons, right?

Yes, that's right. It's a bit of a hack and we should rework that 
interface, because of course there turned out to be various experimental 
exceptions to the initial design that invisible particles would be 
excluded from jets. Muons are of course visible, so if you want jets 
without muons included then you'd need to use a special muon-vetoed 
VetoedFinalState as the input to the jet algorithm. Again, if we can 
find a neat way to set up the interface that suits all the use-cases, we 

Best wishes,

Dr Andy Buckley, SUPA Advanced Research Fellow
Particle Physics Expt Group, University of Edinburgh

The University of Edinburgh is a charitable body, registered in
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