genie::QELKinematicsGenerator Class Reference

Generates values for the kinematic variables describing QEL neutrino interaction events. Is a concrete implementation of the EventRecordVisitorI interface. More...

#include <QELKinematicsGenerator.h>

Inheritance diagram for genie::QELKinematicsGenerator:

Collaboration diagram for genie::QELKinematicsGenerator:

Public Member Functions
	QELKinematicsGenerator ()
	QELKinematicsGenerator (string config)
	~QELKinematicsGenerator ()
void	ProcessEventRecord (GHepRecord *event_rec) const
void	Configure (const Registry &config)
void	Configure (string config)
Public Member Functions inherited from genie::EventRecordVisitorI
virtual	~EventRecordVisitorI ()
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.
virtual AlgStatus_t	GetStatus (void) const
	Get algorithm status.
virtual bool	AllowReconfig (void) const
virtual AlgCmp_t	Compare (const Algorithm *alg) const
	Compare with input algorithm.
virtual void	SetId (const AlgId &id)
	Set algorithm ID.
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.

Private Member Functions
void	SpectralFuncExperimentalCode (GHepRecord *event_rec) const
void	LoadConfig (void)
double	ComputeMaxXSec (const Interaction *in) const

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::KineGeneratorWithCache
	KineGeneratorWithCache ()
	KineGeneratorWithCache (string name)
	KineGeneratorWithCache (string name, string config)
	~KineGeneratorWithCache ()
virtual double	ComputeMaxXSec (const Interaction *in, const int nkey) const
virtual double	MaxXSec (GHepRecord *evrec, const int nkey=0) const
virtual double	FindMaxXSec (const Interaction *in, const int nkey=0) const
virtual void	CacheMaxXSec (const Interaction *in, double xsec, const int nkey=0) const
virtual double	Energy (const Interaction *in) const
virtual CacheBranchFx *	AccessCacheBranch (const Interaction *in, const int nkey=0) const
virtual void	AssertXSecLimits (const Interaction *in, double xsec, double xsec_max) const
Protected Member Functions inherited from genie::EventRecordVisitorI
	EventRecordVisitorI ()
	EventRecordVisitorI (string name)
	EventRecordVisitorI (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.
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.
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.
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
int	AddLowRegistry (Registry *rp, bool owns=true)
	add registry with lowest priority, also update ownership
int	MergeTopRegistry (const Registry &r)
int	AddTopRegisties (const vector< Registry * > &rs, bool owns=false)
	Add registries with top priority, also udated Ownerships.
Protected Attributes inherited from genie::KineGeneratorWithCache
const XSecAlgorithmI *	fXSecModel
double	fSafetyFactor
	ComputeMaxXSec -> ComputeMaxXSec * fSafetyFactor.
std::vector< double >	vSafetyFactors
	MaxXSec -> MaxXSec * fSafetyFactors[nkey].
int	fNumOfSafetyFactors
	Number of given safety factors.
std::vector< string >	vInterpolatorTypes
	Type of interpolator for each key in a branch.
int	fNumOfInterpolatorTypes
	Number of given interpolators types.
double	fMaxXSecDiffTolerance
	max{100*(xsec-maxxsec)/.5*(xsec+maxxsec)} if xsec>maxxsec
double	fEMin
	min E for which maxxsec is cached - forcing explicit calc.
bool	fGenerateUniformly
	uniform over allowed phase space + event weight?
Protected Attributes inherited from genie::Algorithm
bool	fAllowReconfig
bool	fOwnsSubstruc
	true if it owns its substructure (sub-algs,...)
AlgId	fID
	algorithm name and configuration set
vector< Registry * >	fConfVect
vector< bool >	fOwnerships
	ownership for every registry in fConfVect
AlgStatus_t	fStatus
	algorithm execution status
AlgMap *	fOwnedSubAlgMp
	local pool for owned sub-algs (taken out of the factory pool)

Detailed Description

Generates values for the kinematic variables describing QEL neutrino interaction events. Is a concrete implementation of the EventRecordVisitorI interface.

Author

Costas Andreopoulos <c.andreopoulos \at cern.ch> University of Liverpool

Created:\n October 03, 2004

License:\n Copyright (c) 2003-2025, The GENIE Collaboration

For the full text of the license visit http://copyright.genie-mc.org

Definition at line 28 of file QELKinematicsGenerator.h.

Constructor & Destructor Documentation

QELKinematicsGenerator() [1/2]

QELKinematicsGenerator::QELKinematicsGenerator

(

)

Definition at line 37 of file QELKinematicsGenerator.cxx.

                                               :
KineGeneratorWithCache("genie::QELKinematicsGenerator")
{
 
}

References genie::KineGeneratorWithCache::KineGeneratorWithCache().

QELKinematicsGenerator() [2/2]

QELKinematicsGenerator::QELKinematicsGenerator

(

string

config

)

Definition at line 43 of file QELKinematicsGenerator.cxx.

                                                            :
KineGeneratorWithCache("genie::QELKinematicsGenerator", config)
{
 
}

References genie::KineGeneratorWithCache::KineGeneratorWithCache().

~QELKinematicsGenerator()

QELKinematicsGenerator::~QELKinematicsGenerator

(

)

Definition at line 49 of file QELKinematicsGenerator.cxx.

{
 
}

Member Function Documentation

ComputeMaxXSec()

double QELKinematicsGenerator::ComputeMaxXSec ( const Interaction * in ) const

privatevirtual

Implements genie::KineGeneratorWithCache.

Definition at line 465 of file QELKinematicsGenerator.cxx.

{
// Computes the maximum differential cross section in the requested phase
// space. This method overloads KineGeneratorWithCache::ComputeMaxXSec
// method and the value is cached at a circular cache branch for retrieval
// during subsequent event generation.
// The computed max differential cross section does not need to be the exact
// maximum. The number used in the rejection method will be scaled up by a
// safety factor. But it needs to be fast - do not use a very small dQ2 step.
 
  double max_xsec = 0.0;
 
  const KPhaseSpace & kps = interaction->PhaseSpace();
  Range1D_t rQ2 = kps.Limits(kKVQ2);
  if(rQ2.min <=0 || rQ2.max <= rQ2.min) return 0.;
 
  const double logQ2min = TMath::Log(rQ2.min + kASmallNum);
  const double logQ2max = TMath::Log(rQ2.max - kASmallNum);
 
  const int N  = 15;
  const int Nb = 10;
 
  double dlogQ2   = (logQ2max - logQ2min) /(N-1);
  double xseclast = -1;
  bool   increasing;
 
  for(int i=0; i<N; i++) {
     double Q2 = TMath::Exp(logQ2min + i * dlogQ2);
     interaction->KinePtr()->SetQ2(Q2);
     double xsec = fXSecModel->XSec(interaction, kPSQ2fE);
#ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
     LOG("QELKinematics", pDEBUG)  << "xsec(Q2= " << Q2 << ") = " << xsec;
#endif
     max_xsec = TMath::Max(xsec, max_xsec);
     increasing = xsec-xseclast>=0;
     xseclast   = xsec;
 
     // once the cross section stops increasing, I reduce the step size and
     // step backwards a little bit to handle cases that the max cross section
     // is grossly underestimated (very peaky distribution & large step)
     if(!increasing) {
       dlogQ2/=(Nb+1);
       for(int ib=0; ib<Nb; ib++) {
         Q2 = TMath::Exp(TMath::Log(Q2) - dlogQ2);
         if(Q2 < rQ2.min) continue;
         interaction->KinePtr()->SetQ2(Q2);
         xsec = fXSecModel->XSec(interaction, kPSQ2fE);
#ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
         LOG("QELKinematics", pDEBUG)  << "xsec(Q2= " << Q2 << ") = " << xsec;
#endif
         max_xsec = TMath::Max(xsec, max_xsec);
       }
       break;
     }
  }//Q^2
 
  // Apply safety factor, since value retrieved from the cache might
  // correspond to a slightly different energy
  max_xsec *= fSafetyFactor;
 
#ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
  SLOG("QELKinematics", pDEBUG) << interaction->AsString();
  SLOG("QELKinematics", pDEBUG) << "Max xsec in phase space = " << max_xsec;
  SLOG("QELKinematics", pDEBUG) << "Computed using alg = " << *fXSecModel;
#endif
 
  return max_xsec;
}

References genie::Interaction::AsString(), genie::KineGeneratorWithCache::fSafetyFactor, genie::KineGeneratorWithCache::fXSecModel, genie::controls::kASmallNum, genie::Interaction::KinePtr(), genie::kKVQ2, genie::kPSQ2fE, genie::KPhaseSpace::Limits(), LOG, genie::Range1D_t::max, genie::Range1D_t::min, pDEBUG, genie::Interaction::PhaseSpace(), genie::Kinematics::SetQ2(), and SLOG.

Configure() [1/2]

void QELKinematicsGenerator::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 430 of file QELKinematicsGenerator.cxx.

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

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

Configure() [2/2]

void QELKinematicsGenerator::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 436 of file QELKinematicsGenerator.cxx.

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

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

LoadConfig()

void QELKinematicsGenerator::LoadConfig ( void )

private

Definition at line 442 of file QELKinematicsGenerator.cxx.

{
// Load sub-algorithms and config data to reduce the number of registry
// lookups
 
  //-- Safety factor for the maximum differential cross section
        GetParamDef( "MaxXSec-SafetyFactor", fSafetyFactor , 1.25 ) ;
 
  //-- Minimum energy for which max xsec would be cached, forcing explicit
  //   calculation for lower eneries
        GetParamDef( "Cache-MinEnergy", fEMin, 1.00 ) ;
 
  //-- Maximum allowed fractional cross section deviation from maxim cross
  //   section used in rejection method
        GetParamDef( "MaxXSec-DiffTolerance", fMaxXSecDiffTolerance, 999999. ) ;
    assert(fMaxXSecDiffTolerance>=0);
 
  //-- Generate kinematics uniformly over allowed phase space and compute
  //   an event weight?
  GetParamDef( "UniformOverPhaseSpace", fGenerateUniformly, false ) ;
 
}

References genie::KineGeneratorWithCache::fEMin, genie::KineGeneratorWithCache::fGenerateUniformly, genie::KineGeneratorWithCache::fMaxXSecDiffTolerance, genie::KineGeneratorWithCache::fSafetyFactor, and genie::Algorithm::GetParamDef().

Referenced by Configure(), and Configure().

ProcessEventRecord()

void QELKinematicsGenerator::ProcessEventRecord ( GHepRecord * event_rec ) const

virtual

Implements genie::EventRecordVisitorI.

Definition at line 54 of file QELKinematicsGenerator.cxx.

{
  if(fGenerateUniformly) {
    LOG("QELKinematics", pNOTICE)
          << "Generating kinematics uniformly over the allowed phase space";
  }
 
  //-- Get the random number generators
  RandomGen * rnd = RandomGen::Instance();
 
  //-- Access cross section algorithm for running thread
  RunningThreadInfo * rtinfo = RunningThreadInfo::Instance();
  const EventGeneratorI * evg = rtinfo->RunningThread();
  fXSecModel = evg->CrossSectionAlg();
 
  //-- Get the interaction and set the 'trust' bits
  Interaction * interaction = evrec->Summary();
  interaction->SetBit(kISkipProcessChk);
  interaction->SetBit(kISkipKinematicChk);
 
  // store the struck nucleon position for use by the xsec method
  double hitNucPos = evrec->HitNucleon()->X4()->Vect().Mag();
  interaction->InitStatePtr()->TgtPtr()->SetHitNucPosition(hitNucPos);
 
  //-- Note: The kinematic generator would be using the free nucleon cross
  //   section (even for nuclear targets) so as not to double-count nuclear
  //   suppression. This assumes that a) the nuclear suppression was turned
  //   on when computing the cross sections for selecting the current event
  //   and that b) if the event turns out to be unphysical (Pauli-blocked)
  //   the next attempted event will be forced to QEL again.
  //   (discussion with Hugh - GENIE/NeuGEN integration workshop - 07APR2006
  interaction->SetBit(kIAssumeFreeNucleon);
 
  //-- Get the limits for the generated Q2
  const KPhaseSpace & kps = interaction->PhaseSpace();
  Range1D_t Q2 = kps.Limits(kKVQ2);
 
  if(Q2.max <=0 || Q2.min>=Q2.max) {
     LOG("QELKinematics", pWARN) << "No available phase space";
     evrec->EventFlags()->SetBitNumber(kKineGenErr, true);
     genie::exceptions::EVGThreadException exception;
     exception.SetReason("No available phase space");
     exception.SwitchOnFastForward();
     throw exception;
  }
 
  //-- For the subsequent kinematic selection with the rejection method:
  //   Calculate the max differential cross section or retrieve it from the
  //   cache. Throw an exception and quit the evg thread if a non-positive
  //   value is found.
  //   If the kinematics are generated uniformly over the allowed phase
  //   space the max xsec is irrelevant
  double xsec_max = (fGenerateUniformly) ? -1 : this->MaxXSec(evrec);
 
  //-- Try to select a valid Q2 using the rejection method
 
  // kinematical limits
  double Q2min  = Q2.min+kASmallNum;
  double Q2max  = Q2.max-kASmallNum;
//double QD2min = utils::kinematics::Q2toQD2(Q2min);
//double QD2max = utils::kinematics::Q2toQD2(Q2max);
  double xsec   = -1.;
  double gQ2    =  0.;
 
  unsigned int iter = 0;
  bool accept = false;
  while(1) {
     iter++;
     if(iter > kRjMaxIterations) {
        LOG("QELKinematics", pWARN)
          << "Couldn't select a valid Q^2 after " << iter << " iterations";
        evrec->EventFlags()->SetBitNumber(kKineGenErr, true);
        genie::exceptions::EVGThreadException exception;
        exception.SetReason("Couldn't select kinematics");
        exception.SwitchOnFastForward();
        throw exception;
     }
 
     //-- Generate a Q2 value within the allowed phase space
/*
     if(fGenerateUniformly) {
         gQ2 = Q2min + (Q2max-Q2min) * rnd->RndKine().Rndm();
     } else {
         // In unweighted mode - use transform that takes out the dipole form
         double gQD2 = QD2min + (QD2max-QD2min) * rnd->RndKine().Rndm();
         gQ2  = utils::kinematics::QD2toQ2(gQD2);
     }
*/
     gQ2 = Q2min + (Q2max-Q2min) * rnd->RndKine().Rndm();
     interaction->KinePtr()->SetQ2(gQ2);
     LOG("QELKinematics", pINFO) << "Trying: Q^2 = " << gQ2;
 
     //-- Computing cross section for the current kinematics
     xsec = fXSecModel->XSec(interaction, kPSQ2fE);
 
     //-- Decide whether to accept the current kinematics
     if(!fGenerateUniformly) {
        this->AssertXSecLimits(interaction, xsec, xsec_max);
 
        double t = xsec_max * rnd->RndKine().Rndm();
     //double J = kinematics::Jacobian(interaction,kPSQ2fE,kPSQD2fE);
        double J = 1.;
 
#ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
        LOG("QELKinematics", pDEBUG)
            << "xsec= " << xsec << ", J= " << J << ", Rnd= " << t;
#endif
        accept = (t < J*xsec);
     } else {
        accept = (xsec>0);
     }
 
     //-- If the generated kinematics are accepted, finish-up module's job
     if(accept) {
        LOG("QELKinematics", pINFO) << "Selected: Q^2 = " << gQ2;
 
        // reset bits
        interaction->ResetBit(kISkipProcessChk);
        interaction->ResetBit(kISkipKinematicChk);
        interaction->ResetBit(kIAssumeFreeNucleon);
 
        // compute the rest of the kinematical variables
 
        // get neutrino energy at struck nucleon rest frame and the
        // struck nucleon mass (can be off the mass shell)
        const InitialState & init_state = interaction->InitState();
        double E  = init_state.ProbeE(kRfHitNucRest);
        double M = init_state.Tgt().HitNucP4().M();
 
        LOG("QELKinematics", pNOTICE) << "E = " << E << ", M = "<< M;
 
        // The hadronic inv. mass is equal to the recoil nucleon on-shell mass.
        // For QEL/Charm events it is set to be equal to the on-shell mass of
        // the generated charm baryon (Lamda_c+, Sigma_c+ or Sigma_c++)
        // Similarly for strange baryons
        //
        const XclsTag & xcls = interaction->ExclTag();
        int rpdgc = 0;
        if(xcls.IsCharmEvent()) { rpdgc = xcls.CharmHadronPdg();           }
        else if(xcls.IsStrangeEvent()) { rpdgc = xcls.StrangeHadronPdg();           }
        else                    { rpdgc = interaction->RecoilNucleonPdg(); }
        assert(rpdgc);
        double gW = PDGLibrary::Instance()->Find(rpdgc)->Mass();
 
        LOG("QELKinematics", pNOTICE) << "Selected: W = "<< gW;
 
        // (W,Q2) -> (x,y)
        double gx=0, gy=0;
        kinematics::WQ2toXY(E,M,gW,gQ2,gx,gy);
 
        // set the cross section for the selected kinematics
        evrec->SetDiffXSec(xsec,kPSQ2fE);
 
        // for uniform kinematics, compute an event weight as
        // wght = (phase space volume)*(differential xsec)/(event total xsec)
        if(fGenerateUniformly) {
          double vol     = kinematics::PhaseSpaceVolume(interaction,kPSQ2fE);
          double totxsec = evrec->XSec();
          double wght    = (vol/totxsec)*xsec;
          LOG("QELKinematics", pNOTICE)  << "Kinematics wght = "<< wght;
 
          // apply computed weight to the current event weight
          wght *= evrec->Weight();
          LOG("QELKinematics", pNOTICE) << "Current event wght = " << wght;
          evrec->SetWeight(wght);
        }
 
        // lock selected kinematics & clear running values
        interaction->KinePtr()->SetQ2(gQ2, true);
        interaction->KinePtr()->SetW (gW,  true);
        interaction->KinePtr()->Setx (gx,  true);
        interaction->KinePtr()->Sety (gy,  true);
        interaction->KinePtr()->ClearRunningValues();
 
        return;
     }
  }// iterations
}

References genie::KineGeneratorWithCache::AssertXSecLimits(), genie::XclsTag::CharmHadronPdg(), genie::Kinematics::ClearRunningValues(), genie::EventGeneratorI::CrossSectionAlg(), genie::GHepRecord::EventFlags(), genie::Interaction::ExclTag(), genie::KineGeneratorWithCache::fGenerateUniformly, genie::PDGLibrary::Find(), genie::KineGeneratorWithCache::fXSecModel, gQ2, genie::GHepRecord::HitNucleon(), genie::Target::HitNucP4(), genie::Interaction::InitState(), genie::Interaction::InitStatePtr(), genie::PDGLibrary::Instance(), genie::RandomGen::Instance(), genie::RunningThreadInfo::Instance(), genie::XclsTag::IsCharmEvent(), genie::XclsTag::IsStrangeEvent(), genie::controls::kASmallNum, genie::kIAssumeFreeNucleon, genie::Interaction::KinePtr(), genie::kISkipKinematicChk, genie::kISkipProcessChk, genie::kKineGenErr, genie::kKVQ2, genie::kPSQ2fE, genie::kRfHitNucRest, genie::controls::kRjMaxIterations, genie::KPhaseSpace::Limits(), LOG, genie::KineGeneratorWithCache::MaxXSec(), pDEBUG, genie::Interaction::PhaseSpace(), genie::utils::kinematics::PhaseSpaceVolume(), pINFO, pNOTICE, genie::InitialState::ProbeE(), pWARN, genie::Interaction::RecoilNucleonPdg(), genie::RandomGen::RndKine(), genie::RunningThreadInfo::RunningThread(), genie::GHepRecord::SetDiffXSec(), genie::Target::SetHitNucPosition(), genie::Kinematics::SetQ2(), genie::exceptions::EVGThreadException::SetReason(), genie::Kinematics::SetW(), genie::GHepRecord::SetWeight(), genie::Kinematics::Setx(), genie::Kinematics::Sety(), genie::XclsTag::StrangeHadronPdg(), genie::GHepRecord::Summary(), genie::exceptions::EVGThreadException::SwitchOnFastForward(), genie::InitialState::Tgt(), genie::InitialState::TgtPtr(), genie::GHepRecord::Weight(), genie::utils::kinematics::WQ2toXY(), genie::GHepParticle::X4(), and genie::GHepRecord::XSec().

SpectralFuncExperimentalCode()

void QELKinematicsGenerator::SpectralFuncExperimentalCode ( GHepRecord * event_rec ) const

private

Definition at line 233 of file QELKinematicsGenerator.cxx.

{
  //-- Get the random number generators
  RandomGen * rnd = RandomGen::Instance();
 
  //-- Access cross section algorithm for running thread
  RunningThreadInfo * rtinfo = RunningThreadInfo::Instance();
  const EventGeneratorI * evg = rtinfo->RunningThread();
  fXSecModel = evg->CrossSectionAlg();
 
  //-- Get the interaction and set the 'trust' bits
  Interaction * interaction = new Interaction(*evrec->Summary());
  interaction->SetBit(kISkipProcessChk);
  interaction->SetBit(kISkipKinematicChk);
 
  // store the struck nucleon position for use by the xsec method
  double hitNucPos = evrec->HitNucleon()->X4()->Vect().Mag();
  interaction->InitStatePtr()->TgtPtr()->SetHitNucPosition(hitNucPos);
 
  //-- Note: The kinematic generator would be using the free nucleon cross
  //   section (even for nuclear targets) so as not to double-count nuclear
  //   suppression. This assumes that a) the nuclear suppression was turned
  //   on when computing the cross sections for selecting the current event
  //   and that b) if the event turns out to be unphysical (Pauli-blocked)
  //   the next attempted event will be forced to QEL again.
  //   (discussion with Hugh - GENIE/NeuGEN integration workshop - 07APR2006
  interaction->SetBit(kIAssumeFreeNucleon);
 
  //-- Assume scattering off a nucleon on the mass shell (PWIA prescription)
  double Mn  = interaction->InitState().Tgt().HitNucMass(); // PDG mass, take it to be on-shell
  double pxn = interaction->InitState().Tgt().HitNucP4().Px();
  double pyn = interaction->InitState().Tgt().HitNucP4().Py();
  double pzn = interaction->InitState().Tgt().HitNucP4().Pz();
  double En  = interaction->InitState().Tgt().HitNucP4().Energy();
  double En0 = TMath::Sqrt(pxn*pxn + pyn*pyn + pzn*pzn + Mn*Mn);
  double Eb  = En0 - En;
  interaction->InitStatePtr()->TgtPtr()->HitNucP4Ptr()->SetE(En0);
 
  //-- Get the limits for the generated Q2
  const KPhaseSpace & kps = interaction->PhaseSpace();
  Range1D_t Q2 = kps.Limits(kKVQ2);
 
  if(Q2.max <=0 || Q2.min>=Q2.max) {
     LOG("QELKinematics", pWARN) << "No available phase space";
     evrec->EventFlags()->SetBitNumber(kKineGenErr, true);
     genie::exceptions::EVGThreadException exception;
     exception.SetReason("No available phase space");
     exception.SwitchOnFastForward();
     throw exception;
  }
 
  //-- For the subsequent kinematic selection with the rejection method:
  //   Calculate the max differential cross section or retrieve it from the
  //   cache. Throw an exception and quit the evg thread if a non-positive
  //   value is found.
  //   If the kinematics are generated uniformly over the allowed phase
  //   space the max xsec is irrelevant
//  double xsec_max = (fGenerateUniformly) ? -1 : this->MaxXSec(evrec);
  double xsec_max = this->MaxXSec(evrec);
 
  // get neutrino energy at struck nucleon rest frame and the
  // struck nucleon mass (can be off the mass shell)
  const InitialState & init_state = interaction->InitState();
  double E  = init_state.ProbeE(kRfHitNucRest);
 
  LOG("QELKinematics", pNOTICE) << "E = " << E << ", M = "<< Mn;
 
  //-- Try to select a valid Q2 using the rejection method
 
  // kinematical limits
  double Q2min  = Q2.min+kASmallNum;
  double Q2max  = Q2.max-kASmallNum;
  double xsec   = -1.;
  double gQ2    =  0.;
  double gW     =  0.;
  double gx     =  0.;
  double gy     =  0.;
 
  unsigned int iter = 0;
  bool accept = false;
  while(1) {
     iter++;
     if(iter > kRjMaxIterations) {
        LOG("QELKinematics", pWARN)
          << "Couldn't select a valid Q^2 after " << iter << " iterations";
        evrec->EventFlags()->SetBitNumber(kKineGenErr, true);
        genie::exceptions::EVGThreadException exception;
        exception.SetReason("Couldn't select kinematics");
        exception.SwitchOnFastForward();
        throw exception;
     }
 
     //-- Generate a Q2 value within the allowed phase space
     gQ2 = Q2min + (Q2max-Q2min) * rnd->RndKine().Rndm();
     LOG("QELKinematics", pNOTICE) << "Trying: Q^2 = " << gQ2;
 
     // The hadronic inv. mass is equal to the recoil nucleon on-shell mass.
     // For QEL/Charm events it is set to be equal to the on-shell mass of
     // the generated charm baryon (Lamda_c+, Sigma_c+ or Sigma_c++)
     //
     const XclsTag & xcls = interaction->ExclTag();
     int rpdgc = 0;
     if(xcls.IsCharmEvent()) { rpdgc = xcls.CharmHadronPdg();           }
     else                    { rpdgc = interaction->RecoilNucleonPdg(); }
     assert(rpdgc);
     gW = PDGLibrary::Instance()->Find(rpdgc)->Mass();
 
     // (W,Q2) -> (x,y)
     kinematics::WQ2toXY(E,Mn,gW,gQ2,gx,gy);
 
     LOG("QELKinematics", pNOTICE) << "W = "<< gW;
     LOG("QELKinematics", pNOTICE) << "x = "<< gx;
     LOG("QELKinematics", pNOTICE) << "y = "<< gy;
 
     // v
     double gv  = gy * E;
     double gv2 = gv*gv;
 
     LOG("QELKinematics", pNOTICE) << "v = "<< gv;
 
     // v -> v~
     double gvtilde  = gv + Mn - Eb - TMath::Sqrt(Mn*Mn+pxn*pxn+pyn*pyn+pzn*pzn);
     double gvtilde2 = gvtilde*gvtilde;
 
     LOG("QELKinematics", pNOTICE) << "v~ = "<< gvtilde;
 
     // Q~^2
     double gQ2tilde = gQ2 - gv2 + gvtilde2;
 
     LOG("QELKinematics", pNOTICE) << "Q~^2 = "<< gQ2tilde;
 
     // Set updated Q2
     interaction->KinePtr()->SetQ2(gQ2tilde);
 
     //-- Computing cross section for the current kinematics
     xsec = fXSecModel->XSec(interaction, kPSQ2fE);
 
     //-- Decide whether to accept the current kinematics
//     if(!fGenerateUniformly) {
        this->AssertXSecLimits(interaction, xsec, xsec_max);
 
        double t = xsec_max * rnd->RndKine().Rndm();
#ifdef __GENIE_LOW_LEVEL_MESG_ENABLED__
        LOG("QELKinematics", pDEBUG)
            << "xsec= " << xsec << ", Rnd= " << t;
#endif
        accept = (t < xsec);
//     } else {
//        accept = (xsec>0);
//     }
 
     //-- If the generated kinematics are accepted, finish-up module's job
     if(accept) {
        LOG("QELKinematics", pNOTICE) << "Selected: Q^2 = " << gQ2;
 
        // reset bits
//        interaction->ResetBit(kISkipProcessChk);
//        interaction->ResetBit(kISkipKinematicChk);
//        interaction->ResetBit(kIAssumeFreeNucleon);
 
        // set the cross section for the selected kinematics
        evrec->SetDiffXSec(xsec,kPSQ2fE);
 
        // for uniform kinematics, compute an event weight as
        // wght = (phase space volume)*(differential xsec)/(event total xsec)
//        if(fGenerateUniformly) {
//          double vol     = kinematics::PhaseSpaceVolume(interaction,kPSQ2fE);
//          double totxsec = evrec->XSec();
//          double wght    = (vol/totxsec)*xsec;
//          LOG("QELKinematics", pNOTICE)  << "Kinematics wght = "<< wght;
 
          // apply computed weight to the current event weight
//          wght *= evrec->Weight();
//          LOG("QELKinematics", pNOTICE) << "Current event wght = " << wght;
//          evrec->SetWeight(wght);
//        }
 
        // lock selected kinematics & clear running values
//        interaction->KinePtr()->SetQ2(gQ2, true);
//        interaction->KinePtr()->SetW (gW,  true);
//        interaction->KinePtr()->Setx (gx,  true);
//        interaction->KinePtr()->Sety (gy,  true);
//        interaction->KinePtr()->ClearRunningValues();
 
        evrec->Summary()->KinePtr()->SetQ2(gQ2, true);
        evrec->Summary()->KinePtr()->SetW (gW,  true);
        evrec->Summary()->KinePtr()->Setx (gx,  true);
        evrec->Summary()->KinePtr()->Sety (gy,  true);
        evrec->Summary()->KinePtr()->ClearRunningValues();
        delete interaction;
 
        return;
     }
  }// iterations
}

References genie::KineGeneratorWithCache::AssertXSecLimits(), genie::XclsTag::CharmHadronPdg(), genie::Kinematics::ClearRunningValues(), genie::EventGeneratorI::CrossSectionAlg(), genie::GHepRecord::EventFlags(), genie::Interaction::ExclTag(), genie::PDGLibrary::Find(), genie::KineGeneratorWithCache::fXSecModel, gQ2, genie::GHepRecord::HitNucleon(), genie::Target::HitNucMass(), genie::Target::HitNucP4(), genie::Target::HitNucP4Ptr(), genie::Interaction::InitState(), genie::Interaction::InitStatePtr(), genie::PDGLibrary::Instance(), genie::RandomGen::Instance(), genie::RunningThreadInfo::Instance(), genie::XclsTag::IsCharmEvent(), genie::controls::kASmallNum, genie::kIAssumeFreeNucleon, genie::Interaction::KinePtr(), genie::kISkipKinematicChk, genie::kISkipProcessChk, genie::kKineGenErr, genie::kKVQ2, genie::kPSQ2fE, genie::kRfHitNucRest, genie::controls::kRjMaxIterations, genie::KPhaseSpace::Limits(), LOG, genie::KineGeneratorWithCache::MaxXSec(), pDEBUG, genie::Interaction::PhaseSpace(), pNOTICE, genie::InitialState::ProbeE(), pWARN, genie::Interaction::RecoilNucleonPdg(), genie::RandomGen::RndKine(), genie::RunningThreadInfo::RunningThread(), genie::GHepRecord::SetDiffXSec(), genie::Target::SetHitNucPosition(), genie::Kinematics::SetQ2(), genie::exceptions::EVGThreadException::SetReason(), genie::Kinematics::SetW(), genie::Kinematics::Setx(), genie::Kinematics::Sety(), genie::GHepRecord::Summary(), genie::exceptions::EVGThreadException::SwitchOnFastForward(), genie::InitialState::Tgt(), genie::InitialState::TgtPtr(), genie::utils::kinematics::WQ2toXY(), and genie::GHepParticle::X4().

---

The documentation for this class was generated from the following files:

• QELKinematicsGenerator.h
• QELKinematicsGenerator.cxx