G4QGSDiffractiveExcitation.cc

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//
// ------------------------------------------------------------
//      GEANT 4 class implemetation file
//
//      ---------------- G4QGSDiffractiveExcitation --------------
//             by Gunter Folger, October 1998.
//         diffractive Excitation used by strings models
//     Take a projectile and a target
//     excite the projectile and target
//  Essential changed by V. Uzhinsky in November - December 2006
//  in order to put it in a correspondence with original FRITIOF
//  model. Variant of FRITIOF with nucleon de-excitation is implemented.  
// ---------------------------------------------------------------------

// Modified:
//  25-05-07 : G.Folger
//       move from management/G4DiffractiveExcitation to to qgsm/G4QGSDiffractiveExcitation
//                  

#include "globals.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"

#include "G4QGSDiffractiveExcitation.hh"
#include "G4LorentzRotation.hh"
#include "G4ThreeVector.hh"
#include "G4ParticleDefinition.hh"
#include "G4VSplitableHadron.hh"
#include "G4ExcitedString.hh"
//#include "G4ios.hh"

#include "G4Exp.hh"
#include "G4Log.hh"
#include "G4Pow.hh"

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

//#define debugDoubleDiffraction

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

G4QGSDiffractiveExcitation::G4QGSDiffractiveExcitation()
{
}

G4QGSDiffractiveExcitation::~G4QGSDiffractiveExcitation()
{
}


G4bool G4QGSDiffractiveExcitation::
ExciteParticipants(G4VSplitableHadron *projectile, G4VSplitableHadron *target, G4bool ) const
{
  #ifdef debugDoubleDiffraction
    G4cout<<G4endl<<"G4QGSDiffractiveExcitation::ExciteParticipants - Double diffraction."<<G4endl;
    G4cout<<"Proj Targ "<<projectile->GetDefinition()->GetParticleName()<<" "<<target->GetDefinition()->GetParticleName()<<G4endl;
    G4cout<<"Proj 4 Mom "<<projectile->Get4Momentum()<<" "<<projectile->Get4Momentum().mag()<<G4endl;
    G4cout<<"Targ 4 Mom "<<target->Get4Momentum()    <<" "<<target->Get4Momentum().mag()    <<G4endl;
  #endif

  G4LorentzVector Pprojectile=projectile->Get4Momentum();

  // -------------------- Projectile parameters -----------------------------------
  G4bool PutOnMassShell=0;

  G4double M0projectile = Pprojectile.mag();                        // Without de-excitation

  if(M0projectile < projectile->GetDefinition()->GetPDGMass())
  {
    PutOnMassShell=1;
    M0projectile=projectile->GetDefinition()->GetPDGMass();
  }

  // -------------------- Target parameters ----------------------------------------------
  G4LorentzVector Ptarget=target->Get4Momentum();

  G4double M0target = Ptarget.mag();

  if(M0target < target->GetDefinition()->GetPDGMass())
  {
    PutOnMassShell=1;
    M0target=target->GetDefinition()->GetPDGMass();
  }

  G4LorentzVector Psum=Pprojectile+Ptarget;
  G4double S=Psum.mag2();
  G4double SqrtS=std::sqrt(S);

  if (SqrtS < M0projectile + M0target) {return false;}  // The model cannot work for pp-interactions
                                                  // at Plab < 1.3 GeV/c.

  G4double Mprojectile2 = M0projectile * M0projectile;
  G4double Mtarget2     = M0target     * M0target;    //Ptarget.mag2(); // for AA-inter.

  // Transform momenta to cms and then rotate parallel to z axis;

  G4LorentzRotation toCms(-1*Psum.boostVector());

  G4LorentzVector Ptmp=toCms*Pprojectile;

  if ( Ptmp.pz() <= 0. )
  {
    // "String" moving backwards in  CMS, abort collision !!
    //G4cout << " abort Collision!! " << G4endl;
    return false;
  }

  toCms.rotateZ(-1*Ptmp.phi());
  toCms.rotateY(-1*Ptmp.theta());

  G4LorentzRotation toLab(toCms.inverse());

  Pprojectile.transform(toCms);
  Ptarget.transform(toCms);

  G4double PZcms2=(S*S+Mprojectile2*Mprojectile2+Mtarget2*Mtarget2-
         2*S*Mprojectile2-2*S*Mtarget2-2*Mprojectile2*Mtarget2)/4./S;

  if (PZcms2 < 0) {return false;}   // It can be in an interaction with off-shell nuclear nucleon

  G4double PZcms = std::sqrt(PZcms2);

  if (PutOnMassShell)
  {
    if (Pprojectile.z() > 0.)
    {
      Pprojectile.setPz( PZcms);
      Ptarget.setPz(    -PZcms);
    }
    else
    {
      Pprojectile.setPz(-PZcms);
      Ptarget.setPz(     PZcms);
    };

    Pprojectile.setE(std::sqrt(Mprojectile2+sqr(Pprojectile.x())+sqr(Pprojectile.y())+PZcms2));
    Ptarget.setE(    std::sqrt(    Mtarget2+sqr(    Ptarget.x())+sqr(    Ptarget.y())+PZcms2));
  }

  G4double maxPtSquare = PZcms2;

  #ifdef debugDoubleDiffraction
    G4cout << "Pprojectile after boost to CMS: " << Pprojectile <<" "<<Pprojectile.mag()<<G4endl;
    G4cout << "Ptarget     after boost to CMS: " << Ptarget     <<" "<<Ptarget.mag()    <<G4endl;
  #endif

  G4int    PrPDGcode=projectile->GetDefinition()->GetPDGEncoding();
  G4int    absPrPDGcode=std::abs(PrPDGcode);
  G4double MinPrDiffMass(0.);
  G4double AveragePt2(0.);

  if (M0projectile <= projectile->GetDefinition()->GetPDGMass())
  { // Normal projectile 
    if( absPrPDGcode > 1000 )                         //------Projectile is baryon --------
    {
      MinPrDiffMass = 1.16;                       // GeV
      AveragePt2 = 0.3;                           // GeV^2
    }
    else if( absPrPDGcode == 211 || PrPDGcode ==  111) //------Projectile is Pion -----------
    {
      MinPrDiffMass = 1.0;                       // GeV
      AveragePt2 = 0.3;                          // GeV^2
    }
    else if( absPrPDGcode == 321 || absPrPDGcode == 130 || absPrPDGcode == 310) //-Projectile is Kaon-
    {
      MinPrDiffMass = 1.1;                        // GeV
      AveragePt2 = 0.3;                           // GeV^2
    }
    else                                              //------Projectile is undefined, Nucleon assumed
    {
      MinPrDiffMass = 1.16;                       // GeV
      AveragePt2 = 0.3;                           // GeV^2
    }
  }
  else
  { // Excited projectile
    MinPrDiffMass = M0projectile + 220.0*MeV;
    AveragePt2 = 0.3; 
  }

  MinPrDiffMass = MinPrDiffMass * GeV;
  AveragePt2 = AveragePt2 * GeV*GeV;
  //---------------------------------------------
  G4double MinTrDiffMass = 1.16*GeV;

  if (SqrtS < MinPrDiffMass + MinTrDiffMass) {return false;}   // The model cannot work at low energy

  G4double MinPrDiffMass2 = MinPrDiffMass * MinPrDiffMass;
  G4double MinTrDiffMass2 = MinTrDiffMass * MinTrDiffMass;

  G4double Pt2;
  G4double ProjMassT2, ProjMassT;
  G4double TargMassT2, TargMassT;
  G4double PMinusNew, TPlusNew;

  G4LorentzVector Qmomentum;
  G4double Qminus, Qplus;

  G4int whilecount=0;
  do {
    if (whilecount++ >= 500 && (whilecount%100)==0)
      if (whilecount > 1000 ) {
  Qmomentum=G4LorentzVector(0.,0.,0.,0.);
  return false;     //  Ignore this interaction
      }

    //  Generate pt
    Qmomentum=G4LorentzVector(GaussianPt(AveragePt2,maxPtSquare),0);

    Pt2=G4ThreeVector(Qmomentum.vect()).mag2();
    ProjMassT2=MinPrDiffMass2+Pt2;
    ProjMassT =std::sqrt(ProjMassT2);

    TargMassT2=MinTrDiffMass2+Pt2;
    TargMassT =std::sqrt(TargMassT2);

    if (SqrtS < ProjMassT + TargMassT) continue;
 
    PZcms2=(S*S+ProjMassT2*ProjMassT2+TargMassT2*TargMassT2-
      2.*S*ProjMassT2-2.*S*TargMassT2-2.*ProjMassT2*TargMassT2)/4./S;
    if (PZcms2 < 0 ) {PZcms2=0;};
    PZcms =std::sqrt(PZcms2);

    G4double PMinusMin=std::sqrt(ProjMassT2+PZcms2)-PZcms;
    G4double PMinusMax=SqrtS-TargMassT;

    PMinusNew=ChooseP(PMinusMin,PMinusMax);
    Qminus=PMinusNew-Pprojectile.minus();

    G4double TPlusMin=std::sqrt(TargMassT2+PZcms2)-PZcms;
    G4double TPlusMax=SqrtS-ProjMassT;

    TPlusNew=ChooseP(TPlusMin, TPlusMax);
    Qplus=-(TPlusNew-Ptarget.plus());

    Qmomentum.setPz( (Qplus-Qminus)/2 );
    Qmomentum.setE(  (Qplus+Qminus)/2 );

  } while ( (Pprojectile+Qmomentum).mag2() <  MinPrDiffMass2 ||
      (Ptarget    -Qmomentum).mag2() <  MinTrDiffMass2   ); 

  Pprojectile += Qmomentum;
  Ptarget     -= Qmomentum;

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

  #ifdef debugDoubleDiffraction
    G4cout << "Pprojectile after boost to Lab: " << Pprojectile <<" "<<Pprojectile.mag()<<G4endl;
    G4cout << "Ptarget     after boost to Lab: " << Ptarget     <<" "<<Ptarget.mag()    <<G4endl;
  #endif

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

  return true;
}


G4ExcitedString * G4QGSDiffractiveExcitation::
String(G4VSplitableHadron * hadron, G4bool isProjectile) const
{
  hadron->SplitUp();
  G4Parton *start= hadron->GetNextParton();
  if ( start==NULL) 
  { G4cout << " G4QGSDiffractiveExcitation::String() Error:No start parton found"<< G4endl;
    return NULL;
  }
  G4Parton *end  = hadron->GetNextParton();
  if ( end==NULL) 
  { G4cout << " G4QGSDiffractiveExcitation::String() Error:No end parton found"<< G4endl;
    return NULL;
  }

  G4ExcitedString * string;
  if ( isProjectile ) 
  {
    string= new G4ExcitedString(end,start, +1);
  } else {
    string= new G4ExcitedString(start,end, -1);
  }

  string->SetPosition(hadron->GetPosition());

  // momenta of string ends

  G4double maxAvailMomentumSquared=sqr(hadron->Get4Momentum().mag()/2.);

  G4double widthOfPtSquare = 0.5*sqr(GeV);
  G4ThreeVector pt=GaussianPt(widthOfPtSquare,maxAvailMomentumSquared);

  G4LorentzVector Pstart(G4LorentzVector(pt,0.));
  G4LorentzVector Pend;
  Pend.setPx(hadron->Get4Momentum().px() - pt.x());
  Pend.setPy(hadron->Get4Momentum().py() - pt.y());

  G4double tm1=hadron->Get4Momentum().minus() +
         ( Pend.perp2()-Pstart.perp2() ) / hadron->Get4Momentum().plus();

  G4double tm2= std::sqrt( std::max(0., sqr(tm1) -
         4. * Pend.perp2() * hadron->Get4Momentum().minus()
         /  hadron->Get4Momentum().plus() ));

  G4int Sign= isProjectile ? -1 : 1;

  G4double endMinus  = 0.5 * (tm1 + Sign*tm2);
  G4double startMinus= hadron->Get4Momentum().minus() - endMinus;

  G4double startPlus= Pstart.perp2() /  startMinus;
  G4double endPlus  = hadron->Get4Momentum().plus() - startPlus;

  Pstart.setPz(0.5*(startPlus - startMinus));
  Pstart.setE(0.5*(startPlus + startMinus));

  Pend.setPz(0.5*(endPlus - endMinus));
  Pend.setE(0.5*(endPlus + endMinus));

  start->Set4Momentum(Pstart);
  end->Set4Momentum(Pend);

  #ifdef debugQGSdiffExictation
    G4cout << " generated string flavors          " << start->GetPDGcode()   << " / " << end->GetPDGcode() << G4endl;
    G4cout << " generated string momenta:   quark " << start->Get4Momentum() << "mass : " <<start->Get4Momentum().mag()<< G4endl;
    G4cout << " generated string momenta: Diquark " << end ->Get4Momentum()  << "mass : " <<end->Get4Momentum().mag()<< G4endl;
    G4cout << " sum of ends                       " << Pstart+Pend << G4endl;
    G4cout << " Original                          " << hadron->Get4Momentum() << G4endl;
  #endif

  return string;  
}


// --------- private methods ----------------------

G4double G4QGSDiffractiveExcitation::ChooseP(G4double Pmin, G4double Pmax) const
{
  // choose an x between Xmin and Xmax with P(x) ~ 1/x
  //  to be improved...

  G4double range=Pmax-Pmin;

  if ( Pmin <= 0. || range <=0. ) 
  {
    G4cout << " Pmin, range : " << Pmin << " , " << range << G4endl;
    throw G4HadronicException(__FILE__, __LINE__, "G4QGSDiffractiveExcitation::ChooseP : Invalid arguments ");
  }

  G4double P;
  P=Pmin * G4Pow::GetInstance()->powA(Pmax/Pmin,G4UniformRand());
  //debug-hpw cout << "DiffractiveX "<<x<<G4endl;
  return P;
}


G4ThreeVector G4QGSDiffractiveExcitation::GaussianPt(G4double AveragePt2, G4double maxPtSquare) const
{            //  @@ this method is used in FTFModel as well. Should go somewhere common!
  G4double Pt2;

  Pt2 = -AveragePt2 * G4Log(1. + G4UniformRand() * (G4Exp(-maxPtSquare/AveragePt2)-1.));

  G4double Pt=std::sqrt(Pt2);

  G4double phi=G4UniformRand() * twopi;

  return G4ThreeVector (Pt*std::cos(phi), Pt*std::sin(phi), 0.);    
}