[Rivet] Finding GenParticles without a production vertex

[Kiran Daniel Joshi]

Dear Rivet developers,

I'm trying to get access to the GenVertex::position() of the constituents of jets, but I'm finding that going through Jet::particles() -> Particle::genParticle() provides a GenParticle which has no production vertex.
However when going through event::genEvent() and using the HepMC::GenEvent::particle_const_iterator's I get an equivalent GenParticle, but also with the production vertex information.

I've attached a basic analysis which should hopefully describe the issue more clearly.
The output I get from the analysis is:

Rivet.Analysis.TEST_GENPARTICLE: INFO  GenParticle from Jet::particles() :
GenParticle: 10575 ID:22 (P,E)=-0.0322852,-0.00788659,0.0434229,0.0546816 Stat:1 PV:0 EV:0 Pol:(0,0) F:0

Rivet.Analysis.TEST_GENPARTICLE: INFO  GenParticle directly from GenEvent:
GenParticle: 10575 ID:22 (P,E)=-0.0322852,-0.00788659,0.0434229,0.0546816 Stat:1 PV:-137 EV:0 Pol:(0,0) F:0

Where the production vertex (PV) is only filled in the latter case.

Do you have any idea why this might be happening?

(I realise that I'm maybe trying to do something that Rivet wasn't designed for, but nonetheless I thought it should be possible?)

Thanks for your help,
Kiran

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