DISHadronicSystemGenerator.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 <RVersion.h>

#include "Framework/Algorithm/AlgConfigPool.h"
#include "Framework/Conventions/Constants.h"
#include "Framework/Conventions/Controls.h"
#include "Framework/EventGen/EVGThreadException.h"
#include "Framework/GHEP/GHepStatus.h"
#include "Framework/GHEP/GHepParticle.h"
#include "Framework/GHEP/GHepRecord.h"
#include "Framework/GHEP/GHepFlags.h"
#include "Framework/Messenger/Messenger.h"
#include "Framework/Numerical/RandomGen.h"
#include "Framework/ParticleData/PDGLibrary.h"
#include "Framework/ParticleData/PDGCodes.h"
#include "Framework/ParticleData/PDGUtils.h"
#include "Framework/Utils/PrintUtils.h"
#include "Framework/Utils/PhysUtils.h"
#include "Physics/DeepInelastic/EventGen/DISHadronicSystemGenerator.h"

using namespace genie;
using namespace genie::controls;
using namespace genie::constants;
using namespace genie::utils;

//___________________________________________________________________________
DISHadronicSystemGenerator::DISHadronicSystemGenerator() :
HadronicSystemGenerator("genie::DISHadronicSystemGenerator")
{

}
//___________________________________________________________________________
DISHadronicSystemGenerator::DISHadronicSystemGenerator(string config) :
HadronicSystemGenerator("genie::DISHadronicSystemGenerator", config)
{

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

}
//___________________________________________________________________________
void DISHadronicSystemGenerator::ProcessEventRecord(GHepRecord * evrec) const
{
// This method generates the final state hadronic system

  //-- Add an entry for the DIS Pre-Fragm. Hadronic State
  this->AddFinalHadronicSyst(evrec);

  // set W in the Event Summary
  //-- Compute the hadronic system invariant mass
  TLorentzVector p4Had = this->Hadronic4pLAB(evrec);

  Interaction * interaction = evrec->Summary();
  interaction->KinePtr()->SetW( p4Had.M() );

  //-- Add the fragmentation products
  fHadronizationModel -> ProcessEventRecord( evrec ) ;


  //-- Simulate the formation zone if not taken directly from the
  //   hadronization model
  this->SimulateFormationZone(evrec);
}
//___________________________________________________________________________
void DISHadronicSystemGenerator::SimulateFormationZone(
                                                   GHepRecord * evrec) const
{
  LOG("DISHadronicVtx", pDEBUG)
    << "Simulating formation zone for the DIS hadronic system";

  GHepParticle * nucltgt = evrec->TargetNucleus();
  if (!nucltgt) {
    LOG("DISHadronicVtx", pDEBUG)
     << "No nuclear target was found - No need to simulate formation zones";
    return;
  }
  // Compute the nuclear radius & how far away a particle is being tracked by
  // the intranuclear hadron transport
  assert(nucltgt && pdg::IsIon(nucltgt->Pdg()));
  double A = nucltgt->A();
  double R = fR0 * TMath::Power(A, 1./3.);
  R *= TMath::Max(fNR,1.); // particle is tracked much further outside the nuclear boundary as the density is non-zero

  // Decay very short living particles so that we can give the formation
  // zone to the daughters
  this->PreHadronTransportDecays(evrec);

  // Get hadronic system's 3-momentum
  GHepParticle * hadronic_system = evrec->FinalStateHadronicSystem();
  TVector3 p3hadr = hadronic_system->P4()->Vect(); // (px,py,pz)

  // Loop over GHEP and set the formation zone to the right particles
  // Limit the maximum formation zone so that particles escaping the
  // nucleus are placed right outside...

  TObjArrayIter piter(evrec);
  GHepParticle * p = 0;
  int icurr = -1;

  while( (p = (GHepParticle *) piter.Next()) )
  {
    icurr++;

    GHepStatus_t ist = p->Status();
    bool apply_formation_zone = (ist==kIStHadronInTheNucleus);

    if(!apply_formation_zone) continue;

    LOG("DISHadronicVtx", pINFO)
      << "Applying formation-zone to " << p->Name();

    double m = p->Mass();
    int pdgc = p->Pdg();
    const TLorentzVector & p4 = *(p->P4());
    double ct0=0.;
    pdg::IsNucleon(pdgc) ? ct0=fct0nucleon : ct0=fct0pion;
    double fz = phys::FormationZone(m,p4,p3hadr,ct0,fK);

    //-- Apply the formation zone step

    double step = fz;
    TVector3 dr = p->P4()->Vect().Unit();            // unit vector along its direction
 // double c  = kLightSpeed / (units::fm/units::ns); // c in fm/nsec
    dr.SetMag(step);                                 // spatial step size
 // double dt = step/c;                              // temporal step:
    double dt = 0;
    TLorentzVector dx4(dr,dt);                       // 4-vector step
    TLorentzVector x4new = *(p->X4()) + dx4;         // new position

    //-- If the formation zone was large enough that the particle is now outside
    //   the nucleus make sure that it is not placed further away from the
    //   (max distance particles tracked by intranuclear cascade) + ~2 fm
    double epsilon = 2; // fm
    double r       = x4new.Vect().Mag(); // fm
    double rmax    = R+epsilon;
    if(r > rmax) {
        LOG("DISHadronicVtx", pINFO)
          << "Particle was stepped too far away (r = " << r << " fm)";
        LOG("DISHadronicVtx", pINFO)
          << "Placing it ~2 fm away from the furthermost position tracked "
          << "by intranuclear cascades (r' = " << rmax << " fm)";
        double scale = rmax/r;
        x4new *= scale;
    }

    p->SetPosition(x4new);
  }
}
//___________________________________________________________________________
void DISHadronicSystemGenerator::Configure(const Registry & config)
{
  Algorithm::Configure(config);
  this->LoadConfig();
}
//____________________________________________________________________________
void DISHadronicSystemGenerator::Configure(string config)
{
  Algorithm::Configure(config);
  this->LoadConfig();
}
//____________________________________________________________________________
void DISHadronicSystemGenerator::LoadConfig(void)
{
  fHadronizationModel = 0;
  fPreINukeDecayer    = 0;

  //-- Get the requested hadronization model
  fHadronizationModel =
     dynamic_cast<const EventRecordVisitorI *> (this->SubAlg("Hadronizer"));
  assert(fHadronizationModel);

  //-- Handle pre-intranuke decays
  fPreINukeDecayer =
     dynamic_cast<const EventRecordVisitorI *> (this->SubAlg("PreTransportDecayer"));
  assert(fPreINukeDecayer);

  //-- Get flag to determine whether we copy all fragmentation record entries
  //   into the GHEP record or just the ones marked with kf=1
  GetParamDef( "FilterPreFragm", fFilterPreFragmEntries, false ) ;

  //-- Get parameters controlling the nuclear sizes
  GetParam( "NUCL-R0", fR0 ) ;
  GetParam( "NUCL-NR", fNR ) ;

  //-- Get parameters controlling the formation zone simulation
  GetParam( "FZONE-ct0pion", fct0pion ) ;
  GetParam( "FZONE-ct0nucleon",fct0nucleon ) ;
  GetParam( "FZONE-KPt2", fK ) ;

  LOG("DISHadronicVtx", pDEBUG) << "ct0pion     = " << fct0pion    << " fermi";
  LOG("DISHadronicVtx", pDEBUG) << "ct0nucleon  = " << fct0nucleon << " fermi";
  LOG("DISHadronicVtx", pDEBUG) << "K(pt^2) = " << fK;
}
//____________________________________________________________________________