AMNuGammaGenerator.cxx

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//____________________________________________________________________________
/*
 Copyright (c) 2003-2020, The GENIE Collaboration
 For the full text of the license visit http://copyright.genie-mc.org

 Costas Andreopoulos <constantinos.andreopoulos \at cern.ch>
 University of Liverpool & STFC Rutherford Appleton Laboratory 
*/
//____________________________________________________________________________

#include <TMath.h>

#include "Framework/Conventions/Constants.h"
#include "Framework/GHEP/GHepStatus.h"
#include "Framework/GHEP/GHepParticle.h"
#include "Framework/GHEP/GHepRecord.h"
#include "Framework/Messenger/Messenger.h"
#include "Physics/AnomalyMediatedNuGamma/EventGen/AMNuGammaGenerator.h"
#include "Framework/Numerical/RandomGen.h"
#include "Framework/ParticleData/PDGCodes.h"
#include "Framework/ParticleData/PDGUtils.h"
#include "Framework/ParticleData/PDGLibrary.h"

using namespace genie;
using namespace genie::constants;

//___________________________________________________________________________
AMNuGammaGenerator::AMNuGammaGenerator() :
EventRecordVisitorI("genie::AMNuGammaGenerator")
{

}
//___________________________________________________________________________
AMNuGammaGenerator::AMNuGammaGenerator(string config) :
EventRecordVisitorI("genie::AMNuGammaGenerator", config)
{

}
//___________________________________________________________________________
AMNuGammaGenerator::~AMNuGammaGenerator()
{

}
//___________________________________________________________________________
void AMNuGammaGenerator::ProcessEventRecord(GHepRecord * evrec) const
{
  this->AddPhoton(evrec);
  this->AddFinalStateNeutrino(evrec);
  this->AddRecoilNucleon(evrec);
//this->AddTargetRemnant(evrec);
}
//___________________________________________________________________________
void AMNuGammaGenerator::AddPhoton(GHepRecord * evrec) const
{
// Adding the final state photon
//
  LOG("AMNuGammaGenerator", pINFO) << "Adding final state photon";

  RandomGen * rnd = RandomGen::Instance();

  // Get boost vector for transforms between LAB <-> NRF (nucleon rest frame)
  GHepParticle * nuc = evrec->HitNucleon();
  const TLorentzVector & p4nuc_lab = *(nuc->P4());
  TVector3 beta = p4nuc_lab.BoostVector();

  // Get the neutrino 4-momentum at the LAB
  GHepParticle * nu = evrec->Probe();
  const TLorentzVector & p4v_lab = *(nu->P4());

  // Get the neutrino 4-momentum at the NRF
  TLorentzVector p4v_nrf = p4v_lab;
  p4v_nrf.Boost(-1.*beta);

  // Generate the photon cos(theta) with respect to the neutrino direction
  // (at NRF) and a uniform azimuthal angle phi
  double costheta_gamma = -1.0 + 2.0 * rnd->RndKine().Rndm();
  double phi_gamma      =  2.0 * kPi * rnd->RndKine().Rndm();

  // Generate the fraction of the neutrino energy taken by the photon
  double efrac_gamma =  rnd->RndKine().Rndm();

  // Calculate the photon energy at the NRF
  double Ev_nrf = p4v_nrf.Energy();
  double Egamma_nrf = Ev_nrf * efrac_gamma;

  // Calculate the photon momentum components at a rotated NRF (NRF')
  // where z is along the neutrino direction
  double sintheta_gamma = TMath::Sqrt(1-TMath::Power(costheta_gamma,2));
  double pgamma_nrf_p = Egamma_nrf * costheta_gamma; // p(//)
  double pgamma_nrf_t = Egamma_nrf * sintheta_gamma; // p(-|)
  double px = pgamma_nrf_t * TMath::Sin(phi_gamma);
  double py = pgamma_nrf_t * TMath::Cos(phi_gamma);
  double pz = pgamma_nrf_p;

  // Take a unit vector along the neutrino direction @ the NRF
  TVector3 unit_nudir = p4v_nrf.Vect().Unit();

  // Rotate the photon momentum vector from NRF' -> NRF
  TVector3 p3gamma_nrf(px,py,pz);
  p3gamma_nrf.RotateUz(unit_nudir);

  // Get the photon 4-momentum back at the LAB
  TLorentzVector p4gamma_lab(p3gamma_nrf, Egamma_nrf);
  p4gamma_lab.Boost(beta);

  // Add the photon at the event record
  const TLorentzVector & vtx = *(nu->X4());
  GHepParticle p(kPdgGamma,kIStStableFinalState,0,-1,-1,-1,p4gamma_lab,vtx);
  evrec->AddParticle(p);
}
//___________________________________________________________________________
void AMNuGammaGenerator::AddFinalStateNeutrino(GHepRecord * evrec) const
{
// Adding the final state neutrino
// Just use 4-momentum conservation (init_neutrino = photon + final_neutrino)

  LOG("AMNuGammaGenerator", pINFO) << "Adding final state neutrino";

  GHepParticle * nu    = evrec->Probe();                       // incoming v
  GHepParticle * gamma = evrec->Particle(nu->FirstDaughter()); // gamma
  assert(nu);
  assert(gamma);

  const TLorentzVector & vtx = *(nu->X4()); // vtx

  const TLorentzVector & p4nu_lab    = *(nu->P4());
  const TLorentzVector & p4gamma_lab = *(gamma->P4());
  TLorentzVector p4_lab = p4nu_lab - p4gamma_lab;

  GHepParticle p(nu->Pdg(), kIStStableFinalState, 0,-1,-1,-1, p4_lab, vtx);
  evrec->AddParticle(p);
}
//___________________________________________________________________________
void AMNuGammaGenerator::AddRecoilNucleon(GHepRecord * evrec) const
{
// Adding the recoil nucleon.
// Recoil is negligible at the H3 model. However, for nuclear targets, the
// hit nucleon was off-the-mass-shell (bound). Doing some magic here to bring
// it back on-the-mass-shell so that it can be INTRANUKE'ed and appear in
// the final state. The nucleon will keep its original (Fermi) 3-momentum but
// take some energy back from the remnant nucleus. No such tweaking takes
// place for free nucleon targets.

  LOG("AMNuGammaGenerator", pINFO) << "Adding recoil nucleon";

  // Get the interaction target
  GHepParticle * tgt_nucleus = evrec->TargetNucleus();
  bool is_nuclear_target = (tgt_nucleus!=0);

  // Get the hit nucleon
  GHepParticle * hitnuc = evrec->HitNucleon();
  assert(hitnuc);

  // Get the hit nucleon pdg code (= recoil nucleon pdg code)
  int pdgc = hitnuc->Pdg();

  // Get the hit nucleon 4-momentum (LAB)
  const TLorentzVector & p4n = *(hitnuc->P4());
  TLorentzVector p4(p4n);

  // Tweak the 4-momentum to bring the recoil nucleon on-the-mass-shell
  // (for nuclear targets only)
  if (is_nuclear_target) {
    double p = p4.Vect().Mag();
    double m = PDGLibrary::Instance()->Find(pdgc)->Mass();
    double E = TMath::Sqrt(m*m+p*p);
    p4.SetE(E);
  }

  // Get the vtx position
  GHepParticle * neutrino  = evrec->Probe();
  const TLorentzVector & vtx = *(neutrino->X4());

  // Add the recoil nucleon at the event record
  GHepStatus_t ist = (is_nuclear_target) ?
                      kIStHadronInTheNucleus : kIStStableFinalState;
  int mom = evrec->HitNucleonPosition();

  LOG("AMNuGammaGenerator", pINFO)
                  << "Adding recoil baryon [pdgc = " << pdgc << "]";

  GHepParticle p(pdgc, ist, mom,-1,-1,-1, p4, vtx);
//  double w = hitnuc->RemovalEnergy();
///  p.SetRemovalEnergy(w);
  evrec->AddParticle(p);
}
//___________________________________________________________________________
void AMNuGammaGenerator::AddTargetRemnant(GHepRecord * evrec) const
{
// Add the remnant nuclear target at the GHEP record

  LOG("AMNuGammaGenerator", pINFO) << "Adding final state nucleus";

  // Skip for non nuclear targets
  GHepParticle * nucleus = evrec->TargetNucleus();
  if (!nucleus) {
    LOG("AMNuGammaGenerator", pDEBUG)
     << "No nucleus in the initial state - no remnant nucleus to add in the f/s";
    return;
  }

  // Compute A,Z for final state nucleus & get its PDG code and its mass
  //GHepParticle * nucleon = evrec->HitNucleon();

  GHepParticle * hit_nucleon = evrec->HitNucleon(); // hit
  GHepParticle * rec_nucleon = evrec->Particle(hit_nucleon->FirstDaughter()); // recoil

  assert(rec_nucleon);
  int  npdgc = rec_nucleon->Pdg();
  bool is_p  = pdg::IsProton(npdgc);
  int A = nucleus->A();
  int Z = nucleus->Z();
  if (is_p) Z--;
  A--;
  int ipdgc = pdg::IonPdgCode(A, Z);
  TParticlePDG * remnant = PDGLibrary::Instance()->Find(ipdgc);
  if(!remnant) {
      LOG("AMNuGammaGenerator", pFATAL)
          << "No particle with [A = " << A << ", Z = " << Z
                            << ", pdgc = " << ipdgc << "] in PDGLibrary!";
      assert(remnant);
  }

  // Figure out the remnant 4-momentum
  double Mf  = remnant->Mass();
  double Mf2 = TMath::Power(Mf,2);
  double px  = -1.* rec_nucleon->Px();
  double py  = -1.* rec_nucleon->Py();
  double pz  = -1.* rec_nucleon->Pz();
  double E   = TMath::Sqrt(Mf2 + rec_nucleon->P4()->Vect().Mag2());
  E += (hit_nucleon->P4()->E() - rec_nucleon->P4()->E());

  //-- Add the nucleus to the event record
  LOG("AMNuGammaGenerator", pINFO)
       << "Adding nucleus [A = " << A << ", Z = " << Z
                                           << ", pdgc = " << ipdgc << "]";
  int mom = evrec->TargetNucleusPosition();
  evrec->AddParticle(
           ipdgc,kIStStableFinalState, mom,-1,-1,-1, px,py,pz,E, 0,0,0,0);
}
//___________________________________________________________________________