[Rivet] Support for explicit ghosts?

[James Monk]

Hi everyone,

I am trying to run trimmed jets with active area subtraction in Rivet.  Apparently explicit ghosts are needed by fastjet to do this because it needs the ghosts to persist long enough to calculate the areas of the sub jets.  On the other hand, this appears to trip up Rivet’s FastJets projection when it attempts to match the jet’s constituents with the list of particles that were input to the projection, specifically on line 163 of FastJets.cc.  This happens because the jet’s constituents includes all the ghosts, which the projection knows nothing about, so it can’t find them in the _particles map.

Is this known, or am I trying to do things wrong?  I am having to use an uncached version of the FastJet projection because I am feeding it a modified list of input particles after applying some pile-up mitigation, but I don’t think that affects things.

PseudoJet has a method called is_pure_ghost, so I think the solution is for Rivet to use that to ignore any constituent that is a pure ghost - this method returns true if all the constituents of a jet are ghosts, but I presume it works on the ghosts themselves.

cheers,

James