Computes the Valencia MEC model differential cross section. Uses precomputed hadon tensor tables. Is a concrete implementation of the XSecAlgorithmI interface. More...

#include <NievesSimoVacasMECPXSec2016.h>

Inheritance diagram for genie::NievesSimoVacasMECPXSec2016:

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Collaboration diagram for genie::NievesSimoVacasMECPXSec2016:

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Public Member Functions
	NievesSimoVacasMECPXSec2016 ()

	NievesSimoVacasMECPXSec2016 (string config)

virtual	~NievesSimoVacasMECPXSec2016 ()

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 config)

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	fXSecCCScale
	external xsec scaling factor More...

double	fXSecNCScale
	external xsec scaling factor More...

const HadronTensorModelI *	fHadronTensorModel

const XSecIntegratorI *	fXSecIntegrator

const XSecScaleI *	fMECScaleAlg

const QvalueShifter *	fQvalueShifter

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 Valencia MEC model differential cross section. Uses precomputed hadon tensor tables. Is a concrete implementation of the XSecAlgorithmI interface.

Author: Code contributed by J. Schwehr, D. Cherdack, R. Gran and described in arXiv:1601.02038 and some of the refereces there-in, in particular PRD 88 (2013) 113007

Substantial code refactorizations by the core GENIE group.

Refactored in 2018 by S. Gardiner to use the new hadron tensor framework

References:: J. Nieves, I. Ruiz Simo, M.J. Vicente Vacas, Inclusive quasi-elastic neutrino reactions, PRC 83 (2011) 045501

Created:: Mar 22, 2016

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

Definition at line 41 of file NievesSimoVacasMECPXSec2016.h.

Constructor & Destructor Documentation

NievesSimoVacasMECPXSec2016::NievesSimoVacasMECPXSec2016 ( )

Definition at line 29 of file NievesSimoVacasMECPXSec2016.cxx.

                                                          :
 XSecAlgorithmI("genie::NievesSimoVacasMECPXSec2016")
 {
 
 }

NievesSimoVacasMECPXSec2016::NievesSimoVacasMECPXSec2016 ( string config )

Definition at line 35 of file NievesSimoVacasMECPXSec2016.cxx.

                                                                       :
 XSecAlgorithmI("genie::NievesSimoVacasMECPXSec2016", config)
 {
 
 }

NievesSimoVacasMECPXSec2016::~NievesSimoVacasMECPXSec2016 ( )

virtual

Definition at line 41 of file NievesSimoVacasMECPXSec2016.cxx.

 {
 
 }

Member Function Documentation

void NievesSimoVacasMECPXSec2016::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 360 of file NievesSimoVacasMECPXSec2016.cxx.

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

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

void NievesSimoVacasMECPXSec2016::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 366 of file NievesSimoVacasMECPXSec2016.cxx.

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

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

double NievesSimoVacasMECPXSec2016::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 341 of file NievesSimoVacasMECPXSec2016.cxx.

References fXSecIntegrator, and genie::XSecIntegratorI::Integrate().

 {
     double xsec = fXSecIntegrator->Integrate(this,interaction);
     return xsec;
 }

void NievesSimoVacasMECPXSec2016::LoadConfig ( void )

private

Definition at line 372 of file NievesSimoVacasMECPXSec2016.cxx.

References fHadronTensorModel, fMECScaleAlg, fQvalueShifter, fXSecCCScale, fXSecIntegrator, fXSecNCScale, genie::Algorithm::GetConfig(), genie::Algorithm::GetParam(), genie::Algorithm::Id(), LOG, pERROR, and genie::Algorithm::SubAlg().

Referenced by Configure().

 {
   bool good_config = true;
 
   // Cross section scaling factor
   GetParam( "MEC-CC-XSecScale", fXSecCCScale ) ;
   GetParam( "MEC-NC-XSecScale", fXSecNCScale ) ;
 
   fHadronTensorModel = dynamic_cast<const HadronTensorModelI *> ( this->SubAlg("HadronTensorAlg") );
   if( !fHadronTensorModel ) {
     good_config = false ;
     LOG("NievesSimoVacasMECPXSec2016", pERROR) << "The required HadronTensorAlg does not exist. AlgID is : " << SubAlg("HadronTensorAlg")->Id() ;
   }
 
   fXSecIntegrator = dynamic_cast<const XSecIntegratorI *> (this->SubAlg("NumericalIntegrationAlg"));
   if( !fXSecIntegrator ) {
     good_config = false ;
     LOG("NievesSimoVacasMECPXSec2016", pERROR) << "The required NumericalIntegrationAlg does not exist. AlgID is : " << SubAlg("NumericalIntegrationAlg")->Id();
   }
 
   // Read optional QvalueShifter:
   fQvalueShifter = nullptr;
   if( GetConfig().Exists("QvalueShifterAlg") ) {
     fQvalueShifter = dynamic_cast<const QvalueShifter *> ( this->SubAlg("QvalueShifterAlg") );
     if( !fQvalueShifter ) {
       good_config = false ;
       LOG("NievesSimoVacasMECPXSec2016", pERROR) << "The required QvalueShifterAlg does not exist. AlgID is : " << SubAlg("QvalueShifterAlg")->Id() ;
     }
   }
 
   // Read optional MECScaleVsW:
   fMECScaleAlg = nullptr;
   if( GetConfig().Exists("MECScaleAlg") ) {
     fMECScaleAlg = dynamic_cast<const XSecScaleI *> ( this->SubAlg("MECScaleAlg") );
     if( !fMECScaleAlg ) {
       good_config = false ;
       LOG("NievesSimoVacasMECPXSec2016", pERROR) << "The required MECScaleAlg cannot be casted. AlgID is : " << SubAlg("MECScaleAlg")->Id() ;
     }
   }
 
   if( ! good_config ) {
     LOG("NievesSimoVacasMECPXSec2016", pERROR) << "Configuration has failed.";
     exit(78) ;
   }
 
 }

bool NievesSimoVacasMECPXSec2016::ValidProcess ( const Interaction * i ) const

virtual

Can this cross section algorithm handle the input process?

Implements genie::XSecAlgorithmI.

Definition at line 348 of file NievesSimoVacasMECPXSec2016.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 NievesSimoVacasMECPXSec2016::XSec	(	const Interaction *	i,
		KinePhaseSpace_t	k
	)		const

virtual

Compute the cross section for the input interaction.

Todo:: Replace these hard-coded replacements with an equivalent XML configuration

Todo:: Revisit this assumption, and perhaps implement something more robust

Todo:: Shouldn't we get this from the nuclear model?

Implements genie::XSecAlgorithmI.

Definition at line 46 of file NievesSimoVacasMECPXSec2016.cxx.

References genie::KinePhaseSpace::AsString(), genie::LabFrameHadronTensorI::dSigma_dT_dCosTheta(), genie::Interaction::ExclTag(), fHadronTensorModel, fMECScaleAlg, fQvalueShifter, genie::Interaction::FSPrimLepton(), fXSecCCScale, fXSecNCScale, genie::Kinematics::GetKV(), genie::XSecScaleI::GetScaling(), genie::HadronTensorModelI::GetTensor(), genie::Target::HitNucP4(), genie::Target::HitNucPdg(), genie::Interaction::InitState(), genie::pdg::IonPdgCodeToA(), genie::pdg::IonPdgCodeToZ(), genie::ProcessInfo::IsWeakCC(), genie::ProcessInfo::IsWeakNC(), genie::utils::mec::J(), genie::utils::kinematics::Jacobian(), genie::kHT_MEC_DeltaAll, genie::kHT_MEC_Deltapn, genie::kHT_MEC_FullAll, genie::kHT_MEC_Fullpn, genie::Interaction::Kine(), genie::Interaction::KinePtr(), genie::kKVctl, genie::kKVQ0, genie::kKVQ2, genie::kKVQ3, genie::kKVTl, genie::kKVW, genie::XclsTag::KnownResonance(), genie::kPdgClusterNP, genie::kPdgTgtC12, genie::kPdgTgtCa40, genie::kPdgTgtO16, genie::kPSTlctl, genie::kPSWQ2fE, genie::kRfLab, LOG, MAXLOG, pDEBUG, genie::Target::Pdg(), genie::InitialState::Probe(), genie::InitialState::ProbeE(), genie::InitialState::ProbePdg(), genie::Interaction::ProcInfo(), pWARN, genie::HadronTensorI::q0Max(), genie::HadronTensorI::q0Min(), genie::utils::kinematics::Q2(), genie::HadronTensorI::qMagMax(), genie::HadronTensorI::qMagMin(), genie::utils::mec::Qvalue(), genie::Kinematics::SetKV(), genie::InitialState::Tgt(), and genie::utils::kinematics::W().

 {
   // If {W,Q2} have been supplied instead, compute {Tl, ctl}
   // NOTE: The expressions used here neglect Fermi motion and
   // should eventually be revisited. See the "important note"
   // in src/Framework/Utils/KineUtils.cxx about the
   // Jacobian for transforming {W,Q2} --> {Tl, ctl}.
   // - S. Gardiner, 29 July 2020
   if ( kps == kPSWQ2fE ) {
 
     double Q2 = interaction->Kine().GetKV( kKVQ2 );
     double W = interaction->Kine().GetKV( kKVW );
 
     // 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();
 
     // Get the outgoing lepton kinetic energy
     double ml = interaction->FSPrimLepton()->Mass();
     double Tl = Ev - ml - ( (W*W + Q2 - M*M) / (2.*M) );
 
     // Get the outgoing lepton scattering cosine
     double El = Tl + ml;
     double pl = std::sqrt( std::max(0., El*El - ml*ml) );
     double ctl = ( 2.*Ev*El - Q2 - mv*mv - ml*ml ) / ( 2. * pv * pl );
 
     // Set Tl, ctl in the interaction
     interaction->KinePtr()->SetKV( kKVTl, Tl );
     interaction->KinePtr()->SetKV( kKVctl, ctl );
   }
 
   // This function returns d2sigma/(dTmu dcos_mu) in GeV^(-3)
   int target_pdg = interaction->InitState().Tgt().Pdg();
 
   int A_request = pdg::IonPdgCodeToA(target_pdg);
   int Z_request = pdg::IonPdgCodeToZ(target_pdg);
 
   // To generate cross-sections for nuclei other than those with hadron
   // tensors we need to pull both the full cross-section and
   // the pn initial state fraction.
   // Non-isoscalar nuclei are beyond the original published Valencia model
   // and scale with A according to the number of pp, pn, or nn pairs
   // the probe is expected to find.
   // There is some by-hand optimization here, skipping the delta part when
   // only the total cross-section is requested.
   // Possible future models without a Delta had tensor would also use that
   // flag to call this without computing the Delta part.
 
   // Try to look up a hadron tensor in the pool that is an exact match for
   // the target nucleus. If an exact match cannot be found, decide upon a
   // suitable substitute based on the mass number A and proton number Z.
 
   int tensor_pdg = target_pdg;
 
   /// \todo Replace these hard-coded replacements with an equivalent XML
   /// configuration
   if ( ! fHadronTensorModel->GetTensor(tensor_pdg, genie::kHT_MEC_FullAll) )
   {
 
     if ( A_request == 4 && Z_request == 2 ) {
       tensor_pdg = kPdgTgtC12;
       // This is for helium 4, but use carbon tensor
       // the use of nuclear density parameterization is suspicious
       // but some users (MINERvA) need something not nothing.
       // The pn will be exactly 1/3, but pp and nn will be ~1/4
       // Because the combinatorics are different.
       // Could do lithium beryllium boron which you don't need
     }
     else if (A_request < 9) {
       // refuse to do D, T, He3, Li, and some Be, B
       // actually it would work technically, maybe except D, T
       MAXLOG("NievesSimoVacasMEC", pWARN, 10)
           << "Asked to scale to deuterium through boron "
           << target_pdg << " nope, lets not do that.";
       return 0;
     }
     else if (A_request >= 9 && A_request < 15) {
       tensor_pdg = kPdgTgtC12;
       //}
       // could explicitly put in nitrogen for air
       //else if ( A_request >= 14 && A < 15) { // AND CHANGE <=14 to <14.
       //  tensor_pdg = kPdgTgtN14;
     }
     else if (A_request >= 15 && A_request < 22) {
       tensor_pdg = kPdgTgtO16;
     }
     else if (A_request >= 22 && A_request < 33) {
       // of special interest, this gets Al27 and Si28
       tensor_pdg = 1000140280;
     }
     else if (A_request >= 33 && A_request < 50) {
       // of special interest, this gets Ar40 and Ti48
       tensor_pdg = kPdgTgtCa40;
     }
     else if (A_request >= 50 && A_request < 90) {
       // pseudoFe56, also covers many other ferrometals and Ge
       tensor_pdg = 1000280560;
     }
     else if (A_request >= 90 && A_request < 160) {
       // use Ba112 = PseudoCd.  Row5 of Periodic table useless. Ag, Xe?
       tensor_pdg = 1000561120;
     }
     else if (A_request >= 160) {
       // use Rf208 = pseudoPb
       tensor_pdg = 1001042080;
     }
     else {
       MAXLOG("NievesSimoVacasMEC", pWARN, 10)
           << "Asked to scale to a nucleus "
           << target_pdg << " which we don't know yet.";
       return 0;
     }
   }
 
   // Check that the input kinematical point is within the range
   // in which hadron tensors are known (for chosen target)
   double Ev    = interaction->InitState().ProbeE(kRfLab);
   double Tl    = interaction->Kine().GetKV(kKVTl);
   double costl = interaction->Kine().GetKV(kKVctl);
   double ml    = interaction->FSPrimLepton()->Mass();
   double Q0    = interaction->Kine().GetKV(kKVQ0);
   double Q3    = interaction->Kine().GetKV(kKVQ3);
 
   const LabFrameHadronTensorI* tensor
     = dynamic_cast<const LabFrameHadronTensorI*>(
     fHadronTensorModel->GetTensor(tensor_pdg, genie::kHT_MEC_FullAll) );
 
   // If retrieving the tensor failed, complain and return zero
   if ( !tensor ) {
     LOG("NievesSimoVacasMEC", pWARN) << "Failed to load a"
       " hadronic tensor for the nuclide " << tensor_pdg;
     return 0.;
   }
 
   // Assume for now that the range of validity for the "FullAll" hadron
   // tensor is the same as for the partial hadron tensors
   /// \todo Revisit this assumption, and perhaps implement something
   /// more robust
   double Q0min = tensor->q0Min();
   double Q0max = tensor->q0Max();
   double Q3min = tensor->qMagMin();
   double Q3max = tensor->qMagMax();
   if (Q0 < Q0min || Q0 > Q0max || Q3 < Q3min || Q3 > Q3max) {
     return 0.0;
   }
 
   // Get the Q-value needed to calculate the cross sections using the
   // hadron tensor.
   /// \todo Shouldn't we get this from the nuclear model?
   int nu_pdg = interaction->InitState().ProbePdg();
   double Q_value = genie::utils::mec::Qvalue(target_pdg, nu_pdg);
 
   // Apply Qvalue relative shift if needed:
   if( fQvalueShifter ) Q_value += Q_value * fQvalueShifter -> Shift( interaction->InitState().Tgt() ) ;
 
   // By default, we will compute the full cross-section. If a resonance is
   // set, we will calculate the part of the cross-section with an internal
   // Delta line without a final state pion (usually called PPD for pioness
   // Delta decay). If a {p,n} hit dinucleon was set we will calculate the
   // cross-section for that component only (either full or PDD cross-section)
   bool delta = interaction->ExclTag().KnownResonance();
   bool pn    = (interaction->InitState().Tgt().HitNucPdg() == kPdgClusterNP);
 
   double xsec_all = 0.;
   double xsec_pn  = 0.;
   if ( delta ) {
 
     const LabFrameHadronTensorI* tensor_delta_all
       = dynamic_cast<const LabFrameHadronTensorI*>(
       fHadronTensorModel->GetTensor(tensor_pdg, genie::kHT_MEC_DeltaAll) );
 
     if ( !tensor_delta_all ) {
       LOG("NievesSimoVacasMEC", pWARN) << "Failed to load a \"DeltaAll\""
         << " hadronic tensor for nuclide " << tensor_pdg;
       return 0.;
     }
 
     const LabFrameHadronTensorI* tensor_delta_pn
       = dynamic_cast<const LabFrameHadronTensorI*>(
       fHadronTensorModel->GetTensor(tensor_pdg, genie::kHT_MEC_Deltapn) );
 
     if ( !tensor_delta_pn ) {
       LOG("NievesSimoVacasMEC", pWARN) << "Failed to load a \"Deltapn\""
         << " hadronic tensor for nuclide " << tensor_pdg;
       return 0.;
     }
 
     xsec_all = tensor_delta_all->dSigma_dT_dCosTheta(interaction, Q_value);
     xsec_pn = tensor_delta_pn->dSigma_dT_dCosTheta(interaction, Q_value);
 
   }
   else {
 
     const LabFrameHadronTensorI* tensor_full_all
       = dynamic_cast<const LabFrameHadronTensorI*>(
       fHadronTensorModel->GetTensor(tensor_pdg, genie::kHT_MEC_FullAll) );
 
     if ( !tensor_full_all ) {
       LOG("NievesSimoVacasMEC", pWARN) << "Failed to load a \"FullAll\""
         << " hadronic tensor for nuclide " << tensor_pdg;
       return 0.;
     }
 
     const LabFrameHadronTensorI* tensor_full_pn
       = dynamic_cast<const LabFrameHadronTensorI*>(
       fHadronTensorModel->GetTensor(tensor_pdg, genie::kHT_MEC_Fullpn) );
 
     if ( !tensor_full_pn ) {
       LOG("NievesSimoVacasMEC", pWARN) << "Failed to load a \"Fullpn\""
         << " hadronic tensor for nuclide " << tensor_pdg;
       return 0.;
     }
 
     xsec_all = tensor_full_all->dSigma_dT_dCosTheta(interaction, Q_value);
     xsec_pn = tensor_full_pn->dSigma_dT_dCosTheta(interaction, Q_value);
   }
 
   // We need to scale the cross section appropriately if
   // we are using a hadronic tensor for a nuclide that is different
   // from the actual target
   bool need_to_scale = (target_pdg != tensor_pdg);
 
   // would need to trap and treat He3, T, D special here.
   if ( need_to_scale ) {
 
     double PP = Z_request;
     double NN = A_request - PP;
     double P  = pdg::IonPdgCodeToZ(tensor_pdg);
     double N  = pdg::IonPdgCodeToA(tensor_pdg) - P;
 
     double scale_pn = TMath::Sqrt( (PP*NN)/(P*N) );
     double scale_pp = TMath::Sqrt( (PP * (PP - 1.)) / (P * (P - 1.)) );
     double scale_nn = TMath::Sqrt( (NN * (NN - 1.)) / (N * (N - 1.)) );
 
     LOG("NievesSimoVacasMEC", pDEBUG)
         << "Scale pn pp nn for (" << target_pdg << ", " << tensor_pdg << ")"
         << " : " << scale_pn << " " << scale_pp << " " << scale_nn;
 
     // This is an approximation in at least three senses:
     // 1. We are scaling from an isoscalar nucleus using p and n counting
     // 2. We are not using the right qvalue in the had tensor
     // 3. We are not scaling the Delta faster than the non-Delta.
     // The guess is that these are good approximations.
     // A test we could document is to scale from O16 to N14 or C12 using this
     // algorithm and see how many percent deviation we see from the full
     // calculation.
     double temp_all = xsec_all;
     double temp_pn  = xsec_pn * scale_pn;
     if (nu_pdg > 0) {
       // matter neutrinos
       temp_all = xsec_pn * scale_pn + (xsec_all - xsec_pn) * scale_nn;
     }
     else {
       // antineutrinos
       temp_all = xsec_pn * scale_pn + (xsec_all - xsec_pn) * scale_pp;
     }
 
     xsec_all = temp_all;
     xsec_pn  = temp_pn;
 
   }
 
   // Choose the right kind of cross section ("all" or "pn") to return
   // based on whether a {p, n} dinucleon was hit
   double xsec = (pn) ? xsec_pn : xsec_all;
 
   // Apply given scaling factor
   const ProcessInfo& proc_info = interaction->ProcInfo();
   if( proc_info.IsWeakCC() ) xsec *= fXSecCCScale;
   else if( proc_info.IsWeakNC() ) xsec *= fXSecNCScale;
 
   if( fMECScaleAlg ) xsec *= fMECScaleAlg->GetScaling( * interaction ) ;
 
   if ( kps != kPSTlctl && kps != kPSWQ2fE ) {
       LOG("NievesSimoVacasMEC", pWARN)
           << "Doesn't support transformation from "
           << KinePhaseSpace::AsString(kPSTlctl) << " to "
           << KinePhaseSpace::AsString(kps);
       xsec = 0;
   }
   else if ( kps == kPSWQ2fE && xsec != 0. ) {
     double J = utils::kinematics::Jacobian( interaction, kPSTlctl, kps );
     xsec *= J;
   }
 
   return xsec;
 }