G4ElasticHNScattering.cc

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// $Id: G4ElasticHNScattering.cc 74627 2013-10-17 07:04:38Z gcosmo $
//

// ------------------------------------------------------------
//      GEANT 4 class implemetation file
//
//      ---------------- G4ElasticHNScattering --------------
//                   by V. Uzhinsky, March 2008.
//             elastic scattering used by Fritiof model
//                 Take a projectile and a target
//                 scatter the projectile and target
// ---------------------------------------------------------------------

#include "globals.hh"
#include "Randomize.hh"
#include "G4PhysicalConstants.hh"

#include "G4ElasticHNScattering.hh"
#include "G4LorentzRotation.hh"
#include "G4ThreeVector.hh"
#include "G4ParticleDefinition.hh"
#include "G4VSplitableHadron.hh"
#include "G4ExcitedString.hh"
#include "G4FTFParameters.hh"
//#include "G4ios.hh"


//============================================================================

G4ElasticHNScattering::G4ElasticHNScattering() {}


//============================================================================

G4bool G4ElasticHNScattering::ElasticScattering( G4VSplitableHadron* projectile, 
                                                 G4VSplitableHadron* target,
                                                 G4FTFParameters* theParameters ) const {
  projectile->IncrementCollisionCount( 1 );
  target->IncrementCollisionCount( 1 );

  // Projectile parameters
  G4LorentzVector Pprojectile = projectile->Get4Momentum();
  if ( Pprojectile.z() < 0.0 ) return false;
  G4bool PutOnMassShell( false );
  G4double M0projectile = Pprojectile.mag();       
  if ( M0projectile < projectile->GetDefinition()->GetPDGMass() ) {
    PutOnMassShell = true;
    M0projectile = projectile->GetDefinition()->GetPDGMass();
  }
  G4double M0projectile2 = M0projectile * M0projectile;
  G4double AveragePt2 = theParameters->GetAvaragePt2ofElasticScattering();

  // Target parameters
  G4LorentzVector Ptarget = target->Get4Momentum();
  G4double M0target = Ptarget.mag();
  if ( M0target < target->GetDefinition()->GetPDGMass() ) {
    PutOnMassShell = true;
    M0target = target->GetDefinition()->GetPDGMass();
  }   
  G4double M0target2 = M0target * M0target;                      

  // Transform momenta to cms and then rotate parallel to z axis;
  G4LorentzVector Psum;
  Psum = Pprojectile + Ptarget;
  G4LorentzRotation toCms( -1*Psum.boostVector() );
  G4LorentzVector Ptmp = toCms*Pprojectile;
  if ( Ptmp.pz() <= 0.0 ) return false;                                 
  // "String" moving backwards in  CMS, abort collision !
  //G4cout << " abort Collision! " << G4endl;
  toCms.rotateZ( -1*Ptmp.phi() );
  toCms.rotateY( -1*Ptmp.theta() );
  G4LorentzRotation toLab( toCms.inverse() );
  Pprojectile.transform( toCms );
  Ptarget.transform( toCms );

  // Putting on mass-on-shell, if needed
  G4double PZcms2, PZcms;                                          
  G4double S = Psum.mag2();                                          
  G4double SqrtS = std::sqrt( S );
  if ( SqrtS < M0projectile + M0target ) return false;

  PZcms2 = ( S*S + sqr( M0projectile2 ) + sqr( M0target2 )
             - 2*S*M0projectile2 - 2*S*M0target2 - 2*M0projectile2*M0target2 ) / 4.0 / S;

  if ( PZcms2 < 0.0 ) {  // It can be in an interaction with off-shell nuclear nucleon
    if ( M0projectile > projectile->GetDefinition()->GetPDGMass() ) { 
      // An attempt to de-excite the projectile
      // It is assumed that the target is in the ground state
      M0projectile = projectile->GetDefinition()->GetPDGMass();
      M0projectile2 = M0projectile * M0projectile;
      PZcms2= ( S*S + sqr( M0projectile2 ) + sqr( M0target2 )
                - 2*S*M0projectile2 - 2*S*M0target2 - 2*M0projectile2*M0target2 ) / 4.0 / S;
      if ( PZcms2 < 0.0 ) { return false; }  // Nonsuccesful attempt to de-excitate the projectile
    } else {                                  
      return false; // The projectile was not excited, but the energy was too low to put
                    // the target nucleon on mass-shell
    }
  }

  PZcms = std::sqrt( PZcms2 );

  if ( PutOnMassShell ) {
    if ( Pprojectile.z() > 0.0 ) {
      Pprojectile.setPz( PZcms );
      Ptarget.setPz( -PZcms );
    } else {
      Pprojectile.setPz( -PZcms );
      Ptarget.setPz( PZcms );
    };
    Pprojectile.setE( std::sqrt( M0projectile2 + Pprojectile.x() * Pprojectile.x() +
                                                 Pprojectile.y() * Pprojectile.y() + PZcms2 ) );
    Ptarget.setE( std::sqrt( M0target2 + Ptarget.x() * Ptarget.x() + Ptarget.y() * Ptarget.y() +
                             PZcms2 ) );
  }

  G4double maxPtSquare = PZcms2;

  // Now we can calculate the transferred Pt
  G4double Pt2;                                                    
  G4double ProjMassT2, ProjMassT;                                  
  G4double TargMassT2, TargMassT;
  G4LorentzVector Qmomentum;

  do {
    Qmomentum = G4LorentzVector( GaussianPt( AveragePt2, maxPtSquare ), 0.0 );
    Pt2 = G4ThreeVector( Qmomentum.vect() ).mag2();                  
    ProjMassT2 = M0projectile2 + Pt2;                           
    ProjMassT = std::sqrt( ProjMassT2 );                            
    TargMassT2 = M0target2 + Pt2;                               
    TargMassT = std::sqrt( TargMassT2 );                            
  } while ( SqrtS < ProjMassT + TargMassT );

  PZcms2 = ( S*S + sqr( ProjMassT2 ) + sqr( TargMassT2 )                           
             - 2.0*S*ProjMassT2 - 2.0*S*TargMassT2 - 2.0*ProjMassT2*TargMassT2 ) / 4.0 / S;

  if ( PZcms2 < 0.0 ) { PZcms2 = 0.0; };  // to avoid the exactness problem
  PZcms = std::sqrt( PZcms2 );                                    
  Pprojectile.setPz( PZcms );  
  Ptarget.setPz( -PZcms ); 
  Pprojectile += Qmomentum;
  Ptarget     -= Qmomentum;

  // Transform back and update SplitableHadron Participant.
  Pprojectile.transform( toLab );
  Ptarget.transform( toLab );

  // Calculation of the creation time
  projectile->SetTimeOfCreation( target->GetTimeOfCreation() );
  projectile->SetPosition( target->GetPosition() );

  // Creation time and position of target nucleon were determined at
  // ReggeonCascade() of G4FTFModel

  projectile->Set4Momentum( Pprojectile );
  target->Set4Momentum( Ptarget );

  //projectile->IncrementCollisionCount( 1 );
  //target->IncrementCollisionCount( 1 );

  return true;
}


//============================================================================

G4ThreeVector G4ElasticHNScattering::GaussianPt( G4double AveragePt2, 
                                                 G4double maxPtSquare ) const {
  // @@ this method is used in FTFModel as well. Should go somewhere common!
  G4double Pt2( 0.0 );
  if ( AveragePt2 <= 0.0 ) {
    Pt2 = 0.0;
  } else {
    Pt2 = -AveragePt2 * std::log( 1.0 + G4UniformRand() * 
                                        ( std::exp( -maxPtSquare/AveragePt2 ) -1.0 ) ); 
  }
  G4double Pt = std::sqrt( Pt2 );
  G4double phi = G4UniformRand() * twopi;
  return G4ThreeVector( Pt * std::cos( phi ), Pt * std::sin( phi ), 0.0 );    
}


//============================================================================

G4ElasticHNScattering::G4ElasticHNScattering( const G4ElasticHNScattering& ) {
  throw G4HadronicException( __FILE__, __LINE__, 
                             "G4ElasticHNScattering copy contructor not meant to be called" );
}


//============================================================================

G4ElasticHNScattering::~G4ElasticHNScattering() {}


//============================================================================

const G4ElasticHNScattering & G4ElasticHNScattering::operator=( const G4ElasticHNScattering& ) {
  throw G4HadronicException( __FILE__, __LINE__, 
                             "G4ElasticHNScattering = operator not meant to be called" );
}


//============================================================================

int G4ElasticHNScattering::operator==( const G4ElasticHNScattering& ) const {
 throw G4HadronicException( __FILE__, __LINE__, 
                            "G4ElasticHNScattering == operator not meant to be called" );
}


//============================================================================

int G4ElasticHNScattering::operator!=( const G4ElasticHNScattering& ) const {
  throw G4HadronicException( __FILE__, __LINE__, 
                            "G4ElasticHNScattering != operator not meant to be called" );
}