QPMDISPXSec.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 <sstream>

#include <TMath.h>
#include <TH1D.h>

#include "Framework/Algorithm/AlgConfigPool.h"
#include "Framework/Conventions/Units.h"
#include "Physics/DeepInelastic/XSection/DISStructureFuncModelI.h"
#include "Physics/XSectionIntegration/XSecIntegratorI.h"
#include "Framework/Conventions/GBuild.h"
#include "Framework/Conventions/Constants.h"
#include "Framework/Conventions/RefFrame.h"
#include "Framework/Conventions/KineVar.h"
#include "Framework/Conventions/Units.h"
#include "Framework/Messenger/Messenger.h"
#include "Physics/DeepInelastic/XSection/QPMDISPXSec.h"
#include "Framework/ParticleData/PDGCodes.h"
#include "Framework/ParticleData/PDGUtils.h"
#include "Framework/Utils/RunOpt.h"
#include "Framework/Numerical/MathUtils.h"
#include "Framework/Utils/KineUtils.h"
#include "Framework/Utils/Range1.h"
#include "Framework/Utils/KineUtils.h"
#include "Framework/Utils/Cache.h"
#include "Framework/Utils/CacheBranchFx.h"

using std::ostringstream;

using namespace genie;
using namespace genie::constants;
//using namespace genie::units;

//____________________________________________________________________________
QPMDISPXSec::QPMDISPXSec() :
XSecAlgorithmI("genie::QPMDISPXSec")
{
  fInInitPhase = true;
}
//____________________________________________________________________________
QPMDISPXSec::QPMDISPXSec(string config) :
XSecAlgorithmI("genie::QPMDISPXSec", config)
{
  fInInitPhase = true;
}
//____________________________________________________________________________
QPMDISPXSec::~QPMDISPXSec()
{

}
//____________________________________________________________________________
double QPMDISPXSec::XSec(
     const Interaction * interaction, KinePhaseSpace_t kps) const
{
  if(! this -> ValidProcess    (interaction) ) return 0.;
  if(! this -> ValidKinematics (interaction) ) return 0.;

  // Get kinematical & init-state parameters
  const Kinematics &   kinematics = interaction -> Kine();
  const InitialState & init_state = interaction -> InitState();
  const ProcessInfo &  proc_info  = interaction -> ProcInfo();

  double E     = init_state.ProbeE(kRfHitNucRest);
  double ml    = interaction->FSPrimLepton()->Mass();
  double Mnuc  = init_state.Tgt().HitNucMass();
  double x     = kinematics.x();
  double y     = kinematics.y();

  double E2    = E    * E;
  double ml2   = ml   * ml;
  double ml4   = ml2  * ml2;
  double Mnuc2 = Mnuc * Mnuc;

#ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
  LOG("DISPXSec", pDEBUG)
   << "Computing d2xsec/dxdy @ E = " << E << ", x = " << x << ", y = " << y;
#endif

  // One of the xsec terms changes sign for antineutrinos @ DIS/CC

  bool is_nubar_cc = pdg::IsAntiNeutrino(init_state.ProbePdg()) &&
                     proc_info.IsWeakCC();
  int sign = (is_nubar_cc) ? -1 : 1;

  // Calculate the DIS structure functions
  fDISSF.Calculate(interaction);

#ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
  LOG("DISPXSec", pDEBUG) << fDISSF;
#endif

  //
  // Compute the differential cross section
  //

  double g2 = kGF2;
  // For EM interaction replace  G_{Fermi} with :
  // a_{em} * pi / ( sqrt(2) * sin^2(theta_weinberg) * Mass_{W}^2 }
  // See C.Quigg, Gauge Theories of the Strong, Weak and E/M Interactions,
  // ISBN 0-8053-6021-2, p.112 (6.3.57)
  // Also, take int account that the photon propagator is 1/p^2 but the
  // W propagator is 1/(p^2-Mass_{W}^2), so weight the EM case with
  // Mass_{W}^4 / q^4
  // So, overall:
  // G_{Fermi}^2 --> a_{em}^2 * pi^2 / (2 * sin^4(theta_weinberg) * q^{4})
  //
  double Q2 = utils::kinematics::XYtoQ2(E,Mnuc,x,y);
  double Q4 = Q2*Q2;
  if(proc_info.IsEM()) {
    g2 = kAem2 * kPi2 / (2.0 * fSin48w * Q4);
  }
  if (proc_info.IsWeakCC()) {
    g2 = kGF2 * kMw2 * kMw2 / TMath::Power((Q2 + kMw2), 2);
  } else if (proc_info.IsWeakNC()) {
    g2 = kGF2 * kMz2 * kMz2 / TMath::Power((Q2 + kMz2), 2);
  }
  double front_factor = (g2*Mnuc*E) / kPi;

  // Build all dxsec/dxdy terms
  double term1 = y * ( x*y + ml2/(2*E*Mnuc) );
  double term2 = 1 - y - Mnuc*x*y/(2*E) - ml2/(4*E2);
  double term3 = sign * (x*y*(1-y/2) - y*ml2/(4*Mnuc*E));
  double term4 = x*y*ml2/(2*Mnuc*E) + ml4/(4*Mnuc2*E2);
  double term5 = -1.*ml2/(2*Mnuc*E);

#ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
  LOG("DISPXSec", pDEBUG)
    << "\nd2xsec/dxdy ~ (" << term1 << ")*F1+(" << term2 << ")*F2+("
                  << term3 << ")*F3+(" << term4 << ")*F4+(" << term5 << ")*F5";
#endif

  term1 *= fDISSF.F1();
  term2 *= fDISSF.F2();
  term3 *= fDISSF.F3();
  term4 *= fDISSF.F4();
  term5 *= fDISSF.F5();

  double xsec = front_factor * (term1 + term2 + term3 + term4 + term5);
  xsec = TMath::Max(xsec,0.);

#ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
  LOG("DISPXSec", pINFO)
        << "d2xsec/dxdy[FreeN] (E= " << E
                      << ", x= " << x << ", y= " << y << ") = " << xsec;
#endif

   // The algorithm computes d^2xsec/dxdy
  // Check whether variable tranformation is needed
  if(kps!=kPSxyfE) {
    double J = utils::kinematics::Jacobian(interaction,kPSxyfE,kps);
    xsec *= J;
  }

  // If requested return the free nucleon xsec even for input nuclear tgt
  if( interaction->TestBit(kIAssumeFreeNucleon) ) return xsec;

  // Compute nuclear cross section (simple scaling here, corrections must
  // have been included in the structure functions)
  const Target & target = init_state.Tgt();
  int nucpdgc = target.HitNucPdg();
  int NNucl = (pdg::IsProton(nucpdgc)) ? target.Z() : target.N();
  xsec *= NNucl;

  // Apply scaling / if required to reach well known asymmptotic value
  xsec *= fScale;

  // Subtract the inclusive charm production cross section
  interaction->ExclTagPtr()->SetCharm();
  double xsec_charm = fCharmProdModel->XSec(interaction,kps);
  interaction->ExclTagPtr()->UnsetCharm();
#ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
  LOG("DISPXSec", pINFO)
       << "Subtracting charm piece: " << xsec_charm << " / out of " << xsec;
#endif
  xsec = TMath::Max(0., xsec-xsec_charm);
  return xsec;
}
//____________________________________________________________________________
double QPMDISPXSec::Integral(const Interaction * interaction) const
{
  double xsec = fXSecIntegrator->Integrate(this,interaction);
  return xsec;
}
//____________________________________________________________________________
bool QPMDISPXSec::ValidProcess(const Interaction * interaction) const
{
  if(interaction->TestBit(kISkipProcessChk)) return true;

  const ProcessInfo & proc_info  = interaction->ProcInfo();
  if(!proc_info.IsDeepInelastic()) return false;

  const InitialState & init_state = interaction -> InitState();
  int probe_pdg = init_state.ProbePdg();
  if(!pdg::IsLepton(probe_pdg)) return false;

  if(! init_state.Tgt().HitNucIsSet()) return false;

  int hitnuc_pdg = init_state.Tgt().HitNucPdg();
  if(!pdg::IsNeutronOrProton(hitnuc_pdg)) return false;

  return true;
}
//____________________________________________________________________________
void QPMDISPXSec::Configure(const Registry & config)
{
  Algorithm::Configure(config);
  this->LoadConfig();
}
//____________________________________________________________________________
void QPMDISPXSec::Configure(string config)
{
  Algorithm::Configure(config);

  Registry r( "QPMDISPXSec_specific", false ) ;

  RgKey xdefkey = "XSecModel@genie::EventGenerator/DIS-CC-CHARM";
  RgKey local_key = "CharmXSec" ;
  r.Set( local_key, AlgConfigPool::Instance() -> GlobalParameterList() -> GetAlg(xdefkey) ) ;

  Algorithm::Configure(r) ;

  this->LoadConfig();
}
//____________________________________________________________________________
void QPMDISPXSec::LoadConfig(void)
{
  // Access global defaults to use in case of missing parameters

  fDISSFModel = 0;
  fDISSFModel =
     dynamic_cast<const DISStructureFuncModelI *> (this->SubAlg("SFAlg"));
  assert(fDISSFModel);

  fDISSF.SetModel(fDISSFModel); // <-- attach algorithm

  // Cross section scaling factor
  GetParam( "DIS-XSecScale", fScale ) ;

  // sin^4(theta_weinberg)
  double thw  ;
  GetParam( "WeinbergAngle", thw ) ;
  fSin48w = TMath::Power( TMath::Sin(thw), 4 );


  // Since this method would be called every time the current algorithm is
  // reconfigured at run-time, remove all the data cached by this algorithm
  // since they depend on the previous configuration

  if(!fInInitPhase) {
     Cache * cache = Cache::Instance();
     string keysubstr = this->Id().Key() + "/DIS-RES-Join";
     cache->RmMatchedCacheBranches(keysubstr);
  }
  fInInitPhase = false;

  //-- load the differential cross section integrator
  fXSecIntegrator =
      dynamic_cast<const XSecIntegratorI *> (this->SubAlg("XSec-Integrator"));
  assert(fXSecIntegrator);

  // Load the charm production cross section model
  RgKey local_key = "CharmXSec" ;
  RgAlg xalg;
  GetParam( local_key, xalg ) ;
  LOG("DISXSec", pDEBUG)
     << "Loading the cross section model: " << xalg;

  fCharmProdModel = dynamic_cast<const XSecAlgorithmI *> ( this -> SubAlg(local_key) ) ;
  assert(fCharmProdModel);
}
//____________________________________________________________________________