AlvarezRusoCOHPiPDXSec.h

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//____________________________________________________________________________
/*!

\class    genie::alvarezruso::AlvarezRusoCOHPiPDXsec

\brief    5d differential cross section for Alvarez-Ruso Coherent Pion Production xsec

\ref

\author   Steve Dennis
          University of Warwick, Rutherford Appleton Laboratory

\created  05/12/2013

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

#include <TMath.h>
#include <Math/SMatrix.h>
#include <Math/SVector.h>
#include <Math/LorentzVector.h>

#include "Physics/Coherent/XSection/ARSampledNucleus.h"
#include "Physics/Coherent/XSection/ARConstants.h"
#include "Physics/Coherent/XSection/ARWavefunction.h"
#include "Physics/NuclearState/NuclearUtils.h"

#include <complex>

namespace genie
{
namespace alvarezruso
{

class ARWFSolution;

enum current_t{kCC, kNC};
enum flavour_t{kE, kMu, kTau};
enum nutype_t{kNu,kAntiNu};
enum formfactors_t{kNieves, kGarcia};

class AlvarezRusoCOHPiPDXSec
{
  public:

    AlvarezRusoCOHPiPDXSec(unsigned int Z_, unsigned int A_, const current_t current_,
          const flavour_t flavour_ = kE, const nutype_t nutype = kNu,
          const formfactors_t ff_ = kNieves);
    ~AlvarezRusoCOHPiPDXSec();

    // 5d cross section per nucleon
    double DXSec(const double E_nu_, const double E_l_, const double theta_l_,
           const double phi_l_, const double theta_pi_, const double phi_pi_);

    void SetDebug(bool debug)  {  debug_ = debug;  };

    ARConstants      & GetConstants(void);
    ARSampledNucleus & GetNucleus  (void);

    int GetSampling() const {
      return fSampling;
    }

    double GetPiMass() const {
      return fM_pi;
    }
    double GetLeptonMass() const {
      return fM_l;
    }

    private:
        // Fill the ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> >s based on the values from the kinematics
        void SetKinematics();

        // Fill values based on the flavour
        void SetFlavour();

        // Fill values based on the current
        void SetCurrent();

        std::complex<double> DeltaCouplingInMed(ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > delta_momentum,
             ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > pion_momentum, double density_cent);
        double PiDecayVertex(ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > pion_momentum, double mass);
        std::complex<double>  DeltaPropagatorInMed(ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > delta_momentum);
        double DeltaWidthPauliBlocked(ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > delta_momentum, double density);
        double DeltaWidthFree(ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > delta_momentum);
        std::complex<double> H(unsigned int i, unsigned int j) const;
        double DifferentialCrossSection();
        double PionMomentumCM(ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > delta_momentum);
        double PNVertexFactor(ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > momentum, double mass);
        double DeltaSelfEnergyRe(double density);
        double DeltaSelfEnergyIm(double density);
        double DeltaSelfEnergyConstant(double a, double b, double c, double E);
        std::complex<double> NucleonPropagator(ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > nucleon_momentum);

        void NuclearCurrent(ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > q, ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > pdir, ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > pcrs, ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > ppi, std::complex<double>  *jPtr);

        // Fill the wavefunctions
        void SolveWavefunctions();

        //______________________________________________________________
        // Properties

        bool debug_;
        // Nucleus
        unsigned int fZ;
        unsigned int fA;
        unsigned int fSampling;
        // Choice of current
        current_t current;
        // Choice of neutrino flavour
        flavour_t flavour;
        // Chocie of initial neutrino type
        nutype_t nutype;
        // Choice of form-factor approximation
        formfactors_t formfactors;
        // Constants
        ARConstants * fConstants;
        // Nuclear values
        ARSampledNucleus * fNucleus;
        // Wavefunction calculator
        ARWFSolution* fWfsolution;

        // Kinematics of the event
        double fE_nu;     // initial neutrino energy [GeV]
        double fE_l;      // scattered lepton energy [GeV]
        double fTheta_l;  // scattered lepton angle
        double fTheta_pi; // pion angle
        double fPhi;      // angle between lepton and pion

        double fLastE_pi;

        // Four-momenta of particles and transfers involved
        ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > fQ;    // momentum-transfer
        ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > fP_nu;    // incoming neutrino
        ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > fP_l;    // outgoing lepton/neutrino
        ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > fP_pi;    // outgoing pion
        ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > fP_n_i;    // incoming (stationary) nucleon
        ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > fP_n_o;    // outgoing nucleon
        ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > fP_direct;  // intermediary particle (Delta/nucleon) in direct diagrams
        ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > fP_cross;    // intermediary particle (Delta/nucleon) in crossed diagrams

        // Values and constants which will be used during the running
        // Get set to one of the mass values above in the constructor
        double fM_pi;      // mass of the pion
        double fM_l;       // mass of the lepton
        double fg_factor;  // Current factor. if(NC) = 1/2 G^2. if(CC) = 1/2 G^2 cos^2(theta_c)

        // Form factors for PiNDelta decay vertex
        double fF_direct_delta;
        double fF_direct_nucleon;
        double fF_cross_delta;
        double fF_cross_nucleon;

        // Wavefunction
        ARWavefunction* fUwave;
        ARWavefunction* fUwaveDr;
        ARWavefunction* fUwaveDtheta;

        std::complex<double>  fJ_hadronic[4];
};

} //namespace alvarezruso
} //namespace genie
#endif