Computes the MEC differential cross section. Is a concrete implementation of the XSecAlgorithmI interface.
. More...

#include <EmpiricalMECPXSec2015.h>

Inheritance diagram for genie::EmpiricalMECPXSec2015:

Collaboration diagram for genie::EmpiricalMECPXSec2015:

Public Member Functions
	EmpiricalMECPXSec2015 ()

	EmpiricalMECPXSec2015 (string config)

virtual	~EmpiricalMECPXSec2015 ()

double	XSec (const Interaction *i, KinePhaseSpace_t k) const
	Compute the cross section for the input interaction. More...

double	Integral (const Interaction *i) const

bool	ValidProcess (const Interaction *i) const
	Can this cross section algorithm handle the input process? More...

void	Configure (const Registry &config)

void	Configure (string param_set)

Public Member Functions inherited from genie::XSecAlgorithmI
virtual	~XSecAlgorithmI ()

virtual bool	ValidKinematics (const Interaction *i) const
	Is the input kinematical point a physically allowed one? More...

Public Member Functions inherited from genie::Algorithm
virtual	~Algorithm ()

virtual void	FindConfig (void)

virtual const Registry &	GetConfig (void) const

Registry *	GetOwnedConfig (void)

virtual const AlgId &	Id (void) const
	Get algorithm ID. More...

virtual AlgStatus_t	GetStatus (void) const
	Get algorithm status. More...

virtual bool	AllowReconfig (void) const

virtual AlgCmp_t	Compare (const Algorithm *alg) const
	Compare with input algorithm. More...

virtual void	SetId (const AlgId &id)
	Set algorithm ID. More...

virtual void	SetId (string name, string config)

const Algorithm *	SubAlg (const RgKey &registry_key) const

void	AdoptConfig (void)

void	AdoptSubstructure (void)

virtual void	Print (ostream &stream) const
	Print algorithm info. More...

Private Member Functions
void	LoadConfig (void)

Private Attributes
double	fMq2d
	toy model param: `mass' in dipole (Q2 - dependence) form factor (GeV) More...

double	fMass
	toy model param: peak of W distribution (GeV) More...

double	fWidth
	toy model param: width of W distribution (GeV) More...

double	fMECAPower
	power of A relative to carbon More...

double	fFracPN_NC
	toy model param: fraction of nucleon pairs that are pn, not nn or pp More...

double	fFracPN_CC
	toy model param: fraction of nucleon pairs that are pn, not nn or pp More...

double	fFracPN_EM
	toy model param: fraction of nucleon pairs that are pn, not nn or pp More...

double	fFracCCQE
	empirical model param: MEC cross section is taken to be this fraction of CCQE cross section More...

double	fFracNCQE
	empirical model param: MEC cross section is taken to be this fraction of NCQE cross section More...

double	fFracEMQE
	empirical model param: MEC cross section is taken to be this fraction of Rosenbluth xs More...

const XSecAlgorithmI *	fXSecAlgCCQE
	cross section algorithm for CCQE More...

const XSecAlgorithmI *	fXSecAlgNCQE
	cross section algorithm for NCQE More...

const XSecAlgorithmI *	fXSecAlgEMQE
	cross section algorithm for EMQE More...

const XSecIntegratorI *	fXSecIntegrator
	Integrator used for reweighting. More...

bool	fIntegrateForReweighting

Additional Inherited Members
Static Public Member Functions inherited from genie::Algorithm
static string	BuildParamVectKey (const std::string &comm_name, unsigned int i)

static string	BuildParamVectSizeKey (const std::string &comm_name)

static string	BuildParamMatKey (const std::string &comm_name, unsigned int i, unsigned int j)

static string	BuildParamMatRowSizeKey (const std::string &comm_name)

static string	BuildParamMatColSizeKey (const std::string &comm_name)

Protected Member Functions inherited from genie::XSecAlgorithmI
	XSecAlgorithmI ()

	XSecAlgorithmI (string name)

	XSecAlgorithmI (string name, string config)

Protected Member Functions inherited from genie::Algorithm
	Algorithm ()

	Algorithm (string name)

	Algorithm (string name, string config)

void	Initialize (void)

void	DeleteConfig (void)

void	DeleteSubstructure (void)

Registry *	ExtractLocalConfig (const Registry &in) const

Registry *	ExtractLowerConfig (const Registry &in, const string &alg_key) const
	Split an incoming configuration Registry into a block valid for the sub-algo identified by alg_key. More...

template<class T >
bool	GetParam (const RgKey &name, T &p, bool is_top_call=true) const

template<class T >
bool	GetParamDef (const RgKey &name, T &p, const T &def) const

template<class T >
int	GetParamVect (const std::string &comm_name, std::vector< T > &v, bool is_top_call=true) const
	Handle to load vectors of parameters. More...

int	GetParamVectKeys (const std::string &comm_name, std::vector< RgKey > &k, bool is_top_call=true) const

template<class T >
int	GetParamMat (const std::string &comm_name, TMatrixT< T > &mat, bool is_top_call=true) const
	Handle to load matrix of parameters. More...

template<class T >
int	GetParamMatSym (const std::string &comm_name, TMatrixTSym< T > &mat, bool is_top_call=true) const

int	GetParamMatKeys (const std::string &comm_name, std::vector< RgKey > &k, bool is_top_call=true) const

int	AddTopRegistry (Registry *rp, bool owns=true)
	add registry with top priority, also update ownership More...

int	AddLowRegistry (Registry *rp, bool owns=true)
	add registry with lowest priority, also update ownership More...

int	MergeTopRegistry (const Registry &r)

int	AddTopRegisties (const vector< Registry * > &rs, bool owns=false)
	Add registries with top priority, also udated Ownerships. More...

Protected Attributes inherited from genie::Algorithm
bool	fAllowReconfig

bool	fOwnsSubstruc
	true if it owns its substructure (sub-algs,...) More...

AlgId	fID
	algorithm name and configuration set More...

vector< Registry * >	fConfVect

vector< bool >	fOwnerships
	ownership for every registry in fConfVect More...

AlgStatus_t	fStatus
	algorithm execution status More...

AlgMap *	fOwnedSubAlgMp
	local pool for owned sub-algs (taken out of the factory pool) More...

Detailed Description

Computes the MEC differential cross section. Is a concrete implementation of the XSecAlgorithmI interface.
.

Author: Costas Andreopoulos <c.andreopoulos cern.ch> University of Liverpool

Steve Dytman <dytman+ pitt.edu> Pittsburgh University

Created:: May 05, 2009

License:: Copyright (c) 2003-2024, The GENIE Collaboration For the full text of the license visit http://copyright.genie-mc.org

Definition at line 30 of file EmpiricalMECPXSec2015.h.

Constructor & Destructor Documentation

EmpiricalMECPXSec2015::EmpiricalMECPXSec2015 ( )

Definition at line 34 of file EmpiricalMECPXSec2015.cxx.

                                              :
 XSecAlgorithmI("genie::EmpiricalMECPXSec2015")
 {
 
 }

EmpiricalMECPXSec2015::EmpiricalMECPXSec2015 ( string config )

Definition at line 40 of file EmpiricalMECPXSec2015.cxx.

                                                           :
 XSecAlgorithmI("genie::EmpiricalMECPXSec2015", config)
 {
 
 }

EmpiricalMECPXSec2015::~EmpiricalMECPXSec2015 ( )

virtual

Definition at line 46 of file EmpiricalMECPXSec2015.cxx.

 {
 
 }

Member Function Documentation

void EmpiricalMECPXSec2015::Configure ( const Registry & config )

virtual

Configure the algorithm with an external registry The registry is merged with the top level registry if it is owned, Otherwise a copy of it is added with the highest priority

Reimplemented from genie::Algorithm.

Definition at line 353 of file EmpiricalMECPXSec2015.cxx.

References genie::Algorithm::Configure(), and LoadConfig().

 {
   Algorithm::Configure(config);
   this->LoadConfig();
 }

void EmpiricalMECPXSec2015::Configure ( string config )

virtual

Configure the algorithm from the AlgoConfigPool based on param_set string given in input An algorithm contains a vector of registries coming from different xml configuration files, which are loaded according a very precise prioriy This methods will load a number registries in order of priority: 1) "Tunable" parameter set from CommonParametes. This is loaded with the highest prioriry and it is designed to be used for tuning procedure Usage not expected from the user. 2) For every string defined in "CommonParame" the corresponding parameter set will be loaded from CommonParameter.xml 3) parameter set specified by the config string and defined in the xml file of the algorithm 4) if config is not "Default" also the Default parameter set from the same xml file will be loaded Effectively this avoids the repetion of a parameter when it is not changed in the requested configuration

Reimplemented from genie::Algorithm.

Definition at line 359 of file EmpiricalMECPXSec2015.cxx.

References genie::Algorithm::Configure(), genie::AlgConfigPool::Instance(), LoadConfig(), and genie::Registry::Set().

 {
   Algorithm::Configure(config);
 
   Registry* algos = AlgConfigPool::Instance() -> GlobalParameterList() ;
   string global_key_head = "XSecModel@genie::EventGenerator/" ;
   string local_key_head = "XSecModel-" ;
 
   Registry r( "EmpiricalMECPXSec2015_specific", false ) ;
   r.Set( local_key_head + "QEL-NC", algos -> GetAlg( global_key_head + "QEL-NC") ) ;
   r.Set( local_key_head + "QEL-CC", algos -> GetAlg( global_key_head + "QEL-CC") ) ;
   r.Set( local_key_head + "QEL-EM", algos -> GetAlg( global_key_head + "QEL-EM") ) ;
 
   Algorithm::Configure(r) ;
 
   this->LoadConfig();
 }

double EmpiricalMECPXSec2015::Integral ( const Interaction * i ) const

virtual

Integrate the model over the kinematic phase space available to the input interaction (kinematical cuts can be included)

Implements genie::XSecAlgorithmI.

Definition at line 203 of file EmpiricalMECPXSec2015.cxx.

References genie::Target::A(), genie::units::A, fFracCCQE, fFracEMQE, fFracNCQE, fFracPN_CC, fFracPN_EM, fFracPN_NC, fIntegrateForReweighting, fMECAPower, fXSecAlgCCQE, fXSecAlgEMQE, fXSecAlgNCQE, fXSecIntegrator, genie::Target::HitNucPdg(), genie::Interaction::InitState(), genie::XSecAlgorithmI::Integral(), genie::XSecIntegratorI::Integrate(), genie::pdg::IsAntiNeutrino(), genie::ProcessInfo::IsEM(), genie::pdg::IsNeutrino(), genie::ProcessInfo::IsWeakCC(), genie::ProcessInfo::IsWeakNC(), genie::kPdgNeutron, genie::kPdgProton, genie::kRfLab, genie::Target::Pdg(), genie::InitialState::ProbeE(), genie::InitialState::ProbePdg(), genie::Interaction::ProcInfo(), genie::Interaction::QELCC(), genie::Interaction::QELEM(), genie::Interaction::QELNC(), genie::InitialState::Tgt(), and genie::Target::Z().

 {
   // Normally the empirical MEC splines are computed as a fraction of the CCQE
   // ones. In cases where we want to integrate the differential cross section
   // directly (e.g., for reweighting via the XSecShape_CCMEC dial), do that
   // instead.
   if ( fIntegrateForReweighting ) {
     return fXSecIntegrator->Integrate( this, interaction );
   }
 
 // Calculate the CCMEC cross section as a fraction of the CCQE cross section
 // for the given nuclear target at the given energy.
 // Alternative strategy is to calculate the MEC cross section as the difference
 // of CCQE cross section for two different M_A values (eg ~1.3 GeV and ~1.0 GeV)
 // Include hit-object combinatorial factor? Would yield different A-dependence
 // for MEC and QE.
 //
 
   bool iscc = interaction->ProcInfo().IsWeakCC();
   bool isnc = interaction->ProcInfo().IsWeakNC();
   bool isem = interaction->ProcInfo().IsEM();
 
   int    nupdg  = interaction->InitState().ProbePdg();
   int    tgtpdg = interaction->InitState().Tgt().Pdg();
   double E      = interaction->InitState().ProbeE(kRfLab);
   int nucleon_cluster_pdg = interaction->InitState().Tgt().HitNucPdg();
   double Z=interaction->InitState().Tgt().Z();
   double A=interaction->InitState().Tgt().A();
   double N=A-Z;
 
   if(iscc) {
 
      int nucpdg = 0;
      // neutrino CC: calculate the CCQE cross section resetting the
      // hit nucleon cluster to neutron
      if(pdg::IsNeutrino(nupdg)) {
          nucpdg = kPdgNeutron;
      }
      // anti-neutrino CC: calculate the CCQE cross section resetting the
      // hit nucleon cluster to proton
      else
      if(pdg::IsAntiNeutrino(nupdg)) {
          nucpdg = kPdgProton;
      }
      else {
          exit(1);
      }
 
      // Create a tmp QE process
      Interaction * in = Interaction::QELCC(tgtpdg,nucpdg,nupdg,E);
 
      // Calculate cross section for the QE process
      double xsec = fXSecAlgCCQE->Integral(in);
 
     // Add A dependence which is not known from theory
      double fFracADep = 1.;
      if(A>=12) fFracADep = TMath::Power((N/6.),fMECAPower-1.);
 
      // Use tunable fraction
      // FFracCCQE is fraction of QE going to MEC
      // fFracCCQE_cluster is fraction of MEC going to each NN pair
      //     double fFracCCQE = fFracCCQElo;
 
      double fFracCCQE_cluster=0.;
      if(pdg::IsNeutrino(nupdg) && nucleon_cluster_pdg==2000000201) fFracCCQE_cluster= fFracPN_CC;  //n+p
      if(pdg::IsNeutrino(nupdg) && nucleon_cluster_pdg==2000000200) fFracCCQE_cluster= 1.0-fFracPN_CC;  //n+n
      if(pdg::IsAntiNeutrino(nupdg) && nucleon_cluster_pdg==2000000201) fFracCCQE_cluster= fFracPN_CC;   //n+p
      if(pdg::IsAntiNeutrino(nupdg) && nucleon_cluster_pdg==2000000202) fFracCCQE_cluster= 1.0-fFracPN_CC;   //p+p
 
 
      xsec *= fFracCCQE*fFracCCQE_cluster*fFracADep;
 
      // Use gross combinatorial factor (number of 2-nucleon targets over number
      // of 1-nucleon targets) : (A-1)/2
      //     double combfact = (in->InitState().Tgt().A()-1)/2.;
      //     xsec *= combfact;
 
      delete in;
      return xsec;
   }
 
   else if(isnc) {
     int nucpdg = kPdgProton;
     // Create a tmp QE process
     Interaction * inp = Interaction::QELNC(tgtpdg,nucpdg,nupdg,E);
     nucpdg = kPdgNeutron;
     // Create a tmp QE process
     Interaction * inn = Interaction::QELNC(tgtpdg,nucpdg,nupdg,E);
 
     // Calculate cross section for the QE process - avg of p and n - best for isoscalar nuclei
     double xsec = (Z*fXSecAlgNCQE->Integral(inp) + N*fXSecAlgNCQE->Integral(inn))/A;
 
     // Add A dependence which is not known from theory
     double fFracADep = 1.;
     if(A>=12) fFracADep = TMath::Power((A/12.),fMECAPower-1.);
 
     // Use tunable fraction
     // FFracNCQE is fraction of QE going to MEC
     // fFracNCQE_cluster is fraction of MEC going to each NN pair
     double fFracNCQE_cluster=0.;
     if(nucleon_cluster_pdg==2000000200) fFracNCQE_cluster= 0.5*(1-fFracPN_NC);  //n+n
     if(nucleon_cluster_pdg==2000000201) fFracNCQE_cluster= fFracPN_NC;  //n+p
     if(nucleon_cluster_pdg==2000000202) fFracNCQE_cluster= 0.5*(1-fFracPN_NC);  //p+p
     xsec *= fFracNCQE*fFracNCQE_cluster*fFracADep;
     delete inn;
     delete inp;
     return xsec;
   }
 
   else if(isem) {
     int nucpdg = kPdgProton;
     // Create a tmp QE process
     Interaction * inp = Interaction::QELEM(tgtpdg,nucpdg,nupdg,E);
     nucpdg = kPdgNeutron;
     // Create a tmp QE process
     Interaction * inn = Interaction::QELEM(tgtpdg,nucpdg,nupdg,E);
 
     // Calculate cross section for the QE process - avg of p and n - best for isoscalar nuclei
     double xsec = (Z*fXSecAlgEMQE->Integral(inp) + N*fXSecAlgEMQE->Integral(inn))/A;
 
      // Add A dependence which is not known from theory, data wants high A suppression
     double fFracADep = 1.;
     if(A>=12) fFracADep = TMath::Power((A/12.),fMECAPower-1.);
 
     // Use tunable fraction
     // FFracEMQE is fraction of QE going to MEC
     // fFracEMQE_cluster is fraction of MEC going to each NN pair
     double fFracEMQE_cluster=0.;
     if(nucleon_cluster_pdg==2000000200) fFracEMQE_cluster= 0.5*(1-fFracPN_EM);  //n+n
     if(nucleon_cluster_pdg==2000000201) fFracEMQE_cluster= fFracPN_EM;  //n+p
     if(nucleon_cluster_pdg==2000000202) fFracEMQE_cluster= 0.5*(1-fFracPN_EM);  //p+p
     xsec *= fFracEMQE*fFracEMQE_cluster*fFracADep;
     delete inn;
     delete inp;
     return xsec;
   }
 
   return 0;
 }

void EmpiricalMECPXSec2015::LoadConfig ( void )

private

Definition at line 377 of file EmpiricalMECPXSec2015.cxx.

References genie::AlgFactory::AdoptAlgorithm(), fFracCCQE, fFracEMQE, fFracNCQE, fFracPN_CC, fFracPN_EM, fFracPN_NC, fIntegrateForReweighting, fMass, fMECAPower, fMq2d, fWidth, fXSecAlgCCQE, fXSecAlgEMQE, fXSecAlgNCQE, fXSecIntegrator, genie::Algorithm::GetParam(), genie::Algorithm::GetParamDef(), genie::AlgFactory::Instance(), and genie::Algorithm::SubAlg().

Referenced by Configure().

 {
   fXSecAlgCCQE = 0;
   fXSecAlgNCQE = 0;
   fXSecAlgEMQE = 0;
 
   GetParam( "EmpiricalMEC-Mq2d", fMq2d ) ;
   GetParam( "EmpiricalMEC-Mass", fMass ) ;
   GetParam( "EmpiricalMEC-Width", fWidth ) ;
   GetParam( "EmpiricalMEC-APower", fMECAPower ) ;
 
   GetParam( "EmpiricalMEC-FracPN_NC", fFracPN_NC ) ;
   GetParam( "EmpiricalMEC-FracPN_CC", fFracPN_CC ) ;
   GetParam( "EmpiricalMEC-FracPN_EM", fFracPN_EM ) ;
 
   GetParam( "EmpiricalMEC-FracCCQE", fFracCCQE ) ;
   GetParam( "EmpiricalMEC-FracNCQE", fFracNCQE ) ;
   GetParam( "EmpiricalMEC-FracEMQE", fFracEMQE ) ;
 
   string key_head = "XSecModel-" ;
 
   fXSecAlgNCQE =
      dynamic_cast<const XSecAlgorithmI *> ( this -> SubAlg( key_head + "QEL-NC" ) ) ;
   assert(fXSecAlgNCQE);
 
   fXSecAlgCCQE =
      dynamic_cast<const XSecAlgorithmI *> ( this -> SubAlg( key_head + "QEL-CC" ) ) ;
   assert(fXSecAlgCCQE);
 
   fXSecAlgEMQE =
      dynamic_cast<const XSecAlgorithmI *> ( this -> SubAlg( key_head + "QEL-EM" ) ) ;
   assert(fXSecAlgEMQE);
 
   // Get the "fast" configuration of MECXSec. This will be used when integrating
   // the total cross section for reweighting purposes.
   genie::AlgFactory* algf = genie::AlgFactory::Instance();
   fXSecIntegrator = dynamic_cast<const XSecIntegratorI*>( algf->AdoptAlgorithm(
     "genie::MECXSec", "Fast") );
   assert( fXSecIntegrator );
 
   fIntegrateForReweighting = false;
   GetParamDef( "IntegrateForReweighting", fIntegrateForReweighting, false );
 }

bool EmpiricalMECPXSec2015::ValidProcess ( const Interaction * i ) const

virtual

Can this cross section algorithm handle the input process?

Implements genie::XSecAlgorithmI.

Definition at line 343 of file EmpiricalMECPXSec2015.cxx.

References genie::ProcessInfo::IsMEC(), genie::kISkipProcessChk, and genie::Interaction::ProcInfo().

 {
   if(interaction->TestBit(kISkipProcessChk)) return true;
 
   const ProcessInfo &  proc_info  = interaction->ProcInfo();
   if(!proc_info.IsMEC()) return false;
 
   return true;
 }

double EmpiricalMECPXSec2015::XSec	(	const Interaction *	i,
		KinePhaseSpace_t	k
	)		const

virtual

Compute the cross section for the input interaction.

Implements genie::XSecAlgorithmI.

Definition at line 51 of file EmpiricalMECPXSec2015.cxx.

References genie::units::A, genie::KinePhaseSpace::AsString(), genie::PDGLibrary::Find(), fMass, fMq2d, genie::Interaction::FSPrimLepton(), fWidth, genie::Kinematics::GetKV(), genie::Target::HitNucP4(), genie::Target::HitNucPdg(), genie::utils::kinematics::InelQ2Lim_W(), genie::utils::kinematics::electromagnetic::InelQ2Lim_W(), genie::utils::kinematics::InelWLim(), genie::utils::kinematics::electromagnetic::InelWLim(), genie::Interaction::InitState(), genie::PDGLibrary::Instance(), genie::ProcessInfo::IsEM(), genie::ProcessInfo::IsWeakCC(), genie::ProcessInfo::IsWeakNC(), genie::utils::mec::J(), genie::utils::kinematics::Jacobian(), genie::constants::kAem2, genie::Interaction::Kine(), genie::Interaction::KinePtr(), genie::kKVctl, genie::kKVTl, genie::controls::kMinQ2Limit, genie::kPSTlctl, genie::kPSWQ2fE, genie::kRfHitNucRest, genie::kRfLab, LOG, genie::utils::res::Mass(), genie::Range1D_t::max, pDEBUG, genie::InitialState::Probe(), genie::InitialState::ProbeE(), genie::Interaction::ProcInfo(), genie::Kinematics::Q2(), genie::utils::kinematics::Q2(), genie::Kinematics::SetQ2(), genie::Kinematics::SetW(), genie::InitialState::Tgt(), genie::Kinematics::W(), genie::utils::kinematics::W(), and genie::utils::kinematics::WQ2toXY().

 {
 
   // If we've been asked for the kPSTlctl phase space, get W and Q^2 from those
   // variables. You actually need the lepton phi set in order to do the
   // conversion (see the "important note" in src/Framework/Utils/KineUtils.cxx
   // about the kPSTlctl --> kPSWQ2fE Jacobian) when Fermi motion is properly
   // taken into account. For now, I neglect Fermi motion as a stopgap solution.
   // - S. Gardiner, 29 July 2020
   if ( kps == kPSTlctl ) {
 
     // {Tl, ctl} --> {W, Q2}
 
     // Probe properties (mass, energy, momentum)
     const InitialState& init_state = interaction->InitState();
     double mv = init_state.Probe()->Mass();
     double Ev = init_state.ProbeE( kRfLab );
     double pv = std::sqrt( std::max(0., Ev*Ev - mv*mv) );
 
     // Invariant mass of the initial hit nucleon
     const TLorentzVector& hit_nuc_P4 = init_state.Tgt().HitNucP4();
     double M = hit_nuc_P4.M();
 
     // Outgoing lepton mass
     double ml = interaction->FSPrimLepton()->Mass();
 
     // Lab-frame lepton kinetic energy and scattering cosine
     double Tl = interaction->Kine().GetKV( kKVTl );
     double ctl = interaction->Kine().GetKV( kKVctl );
 
     // Q^2 from Tl and ctl
     double El = Tl + ml;
     double pl = std::sqrt( Tl*Tl + 2.*ml*Tl );
     double Q2 = -mv*mv - ml*ml + 2.*Ev*El - 2.*pv*pl*ctl;
 
     // Energy transfer
     double omega = Ev - El;
 
     double W = std::sqrt( std::max(0., M*M - Q2 + 2.*omega*M) );
 
     interaction->KinePtr()->SetW( W );
     interaction->KinePtr()->SetQ2( Q2 );
   }
 
 
 // meson exchange current contribution depends a lot on QE model.
 // This is an empirical model in development, not used in default event generation.
 
 //  if(! this -> ValidProcess    (interaction) ) return 0.;
 //  if(! this -> ValidKinematics (interaction) ) return 0.;
   bool iscc = interaction->ProcInfo().IsWeakCC();
   bool isnc = interaction->ProcInfo().IsWeakNC();
   bool isem = interaction->ProcInfo().IsEM();
 
   const Kinematics &   kinematics = interaction -> Kine();
   double W  = kinematics.W();
   double Q2 = kinematics.Q2();
   //LOG("MEC", pINFO) << "W, Q2 trial= " << W << "  " << Q2 ;
 
   //
   // Do a check whether W,Q2 is allowed. Return 0 otherwise.
   //
   double Ev = interaction->InitState().ProbeE(kRfHitNucRest);  // kRfLab
   int nucleon_cluster_pdg = interaction->InitState().Tgt().HitNucPdg();
   double M2n = PDGLibrary::Instance()->Find(nucleon_cluster_pdg)-> Mass(); // nucleon cluster mass
   double M2n2 = M2n*M2n;
   double ml  = interaction->FSPrimLepton()->Mass();
   Range1D_t Wlim = isem ? genie::utils::kinematics::electromagnetic::InelWLim(Ev, ml, M2n) : genie::utils::kinematics::InelWLim(Ev, M2n, ml);
 
   //LOG("MEC", pINFO) << "Ev, ml, M2n = " << Ev << "  " << ml << "  " << M2n;
   //LOG("MEC", pINFO) << "Wlim= " << Wlim.min << "  " <<Wlim.max ;
   if(W < Wlim.min || W > Wlim.max)
     {double xsec = 0.;
       return xsec;
     }
   //use proper Q2 limit from Controls.h
   Range1D_t Q2lim = isem ? genie::utils::kinematics::electromagnetic::InelQ2Lim_W(Ev, ml, M2n, W) : genie::utils::kinematics::InelQ2Lim_W (Ev, M2n, ml, W, kMinQ2Limit);
 
   //LOG("MEC", pINFO) << "Q2lim= " << Q2lim.min << "  " <<Q2lim.max ;
   if(Q2 < Q2lim.min || Q2 > Q2lim.max)
     {double xsec = 0.;
       return xsec;
     }
 
   //get x and y
   double x = 0.;
   double y = 0.;
   genie::utils::kinematics::WQ2toXY(Ev,M2n,W,Q2,x,y);
   //  LOG("MEC", pINFO) << "x = " << x << ", y = " << y;
   // double Tmu = (1.-y)*Ev;  // UNUSED - comment to quiet compiler warnings
 
   // Calculate d^2xsec/dWdQ2 - first form factor which is common to both
   double Wdep  = TMath::Gaus(W, fMass, fWidth);
   double Q2dep = Q2*TMath::Power((1+Q2/fMq2d),-8.);
   //  double nudep = TMath::Power(Tmu,2.5);
   //  LOG("MEC", pINFO) << "Tmu = " << Tmu << ", nudep = " << nudep;
   double FF2  = Wdep * Q2dep;// * nudep;
   //LOG("MEC", pINFO) << "form factor = " << FF2 << ", Q2 = " << Q2 << ", W = " << W;
 
 // using formulas in Bodek and Budd for (e,e') inclusive cross section
   double xsec = 1.;
   if(isem)  {
       // Calculate scattering angle
   //
   // Q^2 = 4 * E^2 * sin^2 (theta/2) / ( 1 + 2 * (E/M) * sin^2(theta/2) ) =>
   // sin^2 (theta/2) = MQ^2 / (4ME^2 - 2EQ^2)
 
     double E = Ev;
     double E2 = E*E;
     double sin2_halftheta = M2n*Q2 / (4*M2n*E2 - 2*E*Q2);
     //    double sin4_halftheta = TMath::Power(sin2_halftheta, 2.);
     double cos2_halftheta = 1.-sin2_halftheta;
     //    double cos_halftheta  = TMath::Sqrt(cos2_halftheta);
     double tan2_halftheta = sin2_halftheta/cos2_halftheta;
     double Q4 = Q2*Q2;
 
   // Calculate tau and the virtual photon polarization (epsilon)
   double tau     = Q2/(4*M2n2);
   //  double epsilon = 1. / (1. + 2.*(tau/x))*tan2_halftheta); //different than RosenbluthPXSec.cxx
 
   // Calculate the scattered lepton energy
   double Ep  = E / (1. + 2.*(E/M2n)*sin2_halftheta);
   double Ep2 = Ep*Ep;
 
   //calculate cross section - d2sig/dOmega dE for purely transverse process
   xsec = 4*kAem2*Ep2*cos2_halftheta/Q4 * FF2 * (tau/(1+tau) +2*tau*tan2_halftheta);
     }
   // use BB formula which seems to be same as Llewlyn-Smith
   // note B term is only difference between nu and antinu, so both same here
   else if(isnc||iscc){
     double tau     = Q2/(4*M2n2);
     double tau2 = tau*tau;
     double smufac = 4*M2n*Ev - Q2 - ml*ml;
     double A = (ml*ml+Q2)/M2n2 * (tau*(1+tau) - tau2*(1-tau)+4*tau2)/TMath::Power(1+tau,2.) * FF2;
     double C = tau/4/(1+tau) * FF2;
     xsec = A + smufac*smufac*C;   // CC or NC case - Llewelyn-Smith for transverse vector process.
   }
   // Check whether variable tranformation is needed
   if ( kps!=kPSWQ2fE && xsec != 0. ) {
     double J = utils::kinematics::Jacobian(interaction,kPSWQ2fE,kps);
 #ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
     LOG("MEC", pDEBUG)
      << "Jacobian for transformation to: "
                   << KinePhaseSpace::AsString(kps) << ", J = " << J;
 #endif
     xsec *= J;
   }
 
   return xsec;
 }