[Rivet] gen parton matching for jets

[Raghav Kunnawalkam Elayavalli]

Dear Rivet experts

I have a simple question regarding gen parton matching using HepMC::GenParticle in a foreach loop as shown below:

HepMC::GenParticle* truthParton=NULL;
 double truthDelR(0);
 foreach (const HepMC::GenParticle& p, particles(event.genEvent())) {
   if((p->pdg_id() != 21) and (abs(p->pdg_id()) > 6)) continue;
   const double delR = jets.front().delta_R(fastjet::PseudoJet(p->momentum().px(),
p->momentum().py(),
p->momentum().pz(),
p->momentum().e()));
   if(truthParton==NULL){
     truthDelR = delR;
     truthParton = p;
   }
   else if(delR < 0.6 && truthParton->momentum().perp() < p->momentum().perp()){
     //if(null) assign truthParton, updateDelR
     truthDelR = delR;
     truthParton = p;
   }
 }
 _h_TruthDeltaR->fill(truthDelR,weight);

 MC_GENSTUDY_JETCHARGE.cc:256:33: error: cannot initialize a variable of type 'HepMC::GenParticle *' with an lvalue of type 'const HepMC::GenParticle *const'
          foreach (HepMC::GenParticle* p, particles(event.genEvent())) {
                                       ^
/Users/raghav/WORK/RIVET/local/include/boost/foreach.hpp:1107:14: note: expanded from macro 'BOOST_FOREACH'
        for (VAR = BOOST_FOREACH_DEREF(COL); !BOOST_FOREACH_ID(_foreach_continue); BOOST_FOREACH_ID(_foreach_continue) = true)
             ^

Is there a simpler way to do this? it seems like there might be. thanks!

Cheers
Raghav

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