G4QGSDiffractiveExcitation.cc

Go to the documentation of this file.

//
// ********************************************************************
// * License and Disclaimer                                           *
// *                                                                  *
// * The  Geant4 software  is  copyright of the Copyright Holders  of *
// * the Geant4 Collaboration.  It is provided  under  the terms  and *
// * conditions of the Geant4 Software License,  included in the file *
// * LICENSE and available at  http://cern.ch/geant4/license .  These *
// * include a list of copyright holders.                             *
// *                                                                  *
// * Neither the authors of this software system, nor their employing *
// * institutes,nor the agencies providing financial support for this *
// * work  make  any representation or  warranty, express or implied, *
// * regarding  this  software system or assume any liability for its *
// * use.  Please see the license in the file  LICENSE  and URL above *
// * for the full disclaimer and the limitation of liability.         *
// *                                                                  *
// * This  code  implementation is the result of  the  scientific and *
// * technical work of the GEANT4 collaboration.                      *
// * By using,  copying,  modifying or  distributing the software (or *
// * any work based  on the software)  you  agree  to acknowledge its *
// * use  in  resulting  scientific  publications,  and indicate your *
// * acceptance of all terms of the Geant4 Software license.          *
// ********************************************************************
//
//
// $Id: G4QGSDiffractiveExcitation.cc 100828 2016-11-02 15:25:59Z gcosmo $
// ------------------------------------------------------------
//      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"


G4QGSDiffractiveExcitation::G4QGSDiffractiveExcitation()
{
}

G4QGSDiffractiveExcitation::~G4QGSDiffractiveExcitation()
{
}


G4bool G4QGSDiffractiveExcitation::
ExciteParticipants(G4VSplitableHadron *projectile, G4VSplitableHadron *target) const
{
  G4LorentzVector Pprojectile=projectile->Get4Momentum();

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

  //G4double M0projectile=projectile->GetDefinition()->GetPDGMass();  // With de-excitation
  G4double M0projectile = Pprojectile.mag();                        // Without de-excitation

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

  G4double Mprojectile2 = M0projectile * M0projectile;

  G4int    PDGcode=projectile->GetDefinition()->GetPDGEncoding();
  G4int    absPDGcode=std::abs(PDGcode);
  G4double ProjectileDiffCut;
  G4double AveragePt2;

  if( absPDGcode > 1000 )                        //------Projectile is baryon --------
  {
    ProjectileDiffCut = 1.1;                    // GeV
    AveragePt2 = 0.3;                           // GeV^2
  }
  else if( absPDGcode == 211 || PDGcode ==  111) //------Projectile is Pion -----------
  {
    ProjectileDiffCut = 1.0;                   // GeV
    AveragePt2 = 0.3;                          // GeV^2
  }
  else if( absPDGcode == 321 || PDGcode == -311) //------Projectile is Kaon -----------
  {
    ProjectileDiffCut = 1.1;                    // GeV
    AveragePt2 = 0.3;                           // GeV^2
  }
  else                                           //------Projectile is undefined, Nucleon assumed
  {
    ProjectileDiffCut = 1.1;                    // GeV
    AveragePt2 = 0.3;                           // GeV^2
  };

  ProjectileDiffCut = ProjectileDiffCut * GeV;
  AveragePt2 = AveragePt2 * GeV*GeV;

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

  G4double M0target = Ptarget.mag();

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

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

  G4double NuclearNucleonDiffCut = 1.1*GeV;

  G4double ProjectileDiffCut2 = ProjectileDiffCut * ProjectileDiffCut;
  G4double NuclearNucleonDiffCut2 = NuclearNucleonDiffCut * NuclearNucleonDiffCut;

  // 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. )
  {
    // "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 Pt2;
  G4double ProjMassT2, ProjMassT;
  G4double TargMassT2, TargMassT;
  G4double PZcms2, PZcms;
  G4double PMinusNew, TPlusNew;

  G4double S=Psum.mag2();
  G4double SqrtS=std::sqrt(S);

  if(SqrtS < 2200*MeV) {return false;}   // The model cannot work for pp-interactions
  // at Plab < 1.3 GeV/c. Uzhi

  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

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

  G4double maxPtSquare = PZcms2;

  //G4cout << "Pprojectile aft boost : " << Pprojectile << G4endl;
  //G4cout << "Ptarget aft boost : " << Ptarget << G4endl;
  //       G4cout << "cms aft boost : " << (Pprojectile+ Ptarget) << G4endl;
  //       G4cout << " Projectile Xplus / Xminus : " <<
  //             Pprojectile.plus() << " / " << Pprojectile.minus() << G4endl;
  //       G4cout << " Target Xplus / Xminus : " <<
  //             Ptarget.plus() << " / " << Ptarget.minus() << G4endl;

  G4LorentzVector Qmomentum;
  G4double Qminus, Qplus;

  G4int whilecount=0;
  do {
    //  Generate pt

    if (whilecount++ >= 500 && (whilecount%100)==0)
      //G4cout << "G4QGSDiffractiveExcitation::ExciteParticipants possibly looping"
      //       << ", loop count/ maxPtSquare : "
      //       << whilecount << " / " << maxPtSquare << G4endl;

    if (whilecount > 1000 )
    {
      Qmomentum=G4LorentzVector(0.,0.,0.,0.);
      return false;       //  Ignore this interaction
    }

    Qmomentum=G4LorentzVector(GaussianPt(AveragePt2,maxPtSquare),0);

    //G4cout << "generated Pt " << Qmomentum << G4endl;
    //G4cout << "Pprojectile with pt : " << Pprojectile+Qmomentum << G4endl;
    //G4cout << "Ptarget with pt : " << Ptarget-Qmomentum << G4endl;

    //  Momentum transfer
    /*
    G4double Xmin = minmass / ( Pprojectile.e() + Ptarget.e() );
    G4double Xmax=1.;
    G4double Xplus =ChooseX(Xmin,Xmax);
    G4double Xminus=ChooseX(Xmin,Xmax);

    //G4cout << " X-plus  " << Xplus << G4endl;
    //G4cout << " X-minus " << Xminus << G4endl;

    G4double pt2=G4ThreeVector(Qmomentum.vect()).mag2();
    G4double Qplus =-1 * pt2 / Xminus/Ptarget.minus();
    G4double Qminus=     pt2 / Xplus /Pprojectile.plus();
    */

    Pt2=G4ThreeVector(Qmomentum.vect()).mag2();
    ProjMassT2=Mprojectile2+Pt2;
    ProjMassT =std::sqrt(ProjMassT2);

    TargMassT2=Mtarget2+Pt2;
    TargMassT =std::sqrt(TargMassT2);

    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 );

    //G4cout << "Qplus / Qminus " << Qplus << " / " << Qminus<<G4endl;
    //G4cout << "pt2" << pt2 << G4endl;
    //G4cout << "Qmomentum " << Qmomentum << G4endl;
    //G4cout << " Masses (P/T) : " << (Pprojectile+Qmomentum).mag() <<
    //             " / " << (Ptarget-Qmomentum).mag() << G4endl;
  /*
  } while ( (Pprojectile+Qmomentum).mag2() <= Mprojectile2 ||
             (Ptarget-Qmomentum).mag2()     <= Mtarget2 );
  */
  } while (  /* Loop checking, 26.10.2015, A.Ribon */
            ( (Pprojectile+Qmomentum).mag2() <  Mprojectile2       ||        // No without excitation
          (Ptarget    -Qmomentum).mag2() <  Mtarget2             ) ||  
          ( (Pprojectile+Qmomentum).mag2()  <  ProjectileDiffCut2 &&     // No double Diffraction
          (Ptarget    -Qmomentum).mag2()  <  NuclearNucleonDiffCut2) ); 

  if((Ptarget-Qmomentum).mag2() < NuclearNucleonDiffCut2)         // Uzhi Projectile diffraction
  {
    G4double TMinusNew=SqrtS-PMinusNew;
    Qminus=Ptarget.minus()-TMinusNew;
    TPlusNew=TargMassT2/TMinusNew;
    Qplus=Ptarget.plus()-TPlusNew;

    Qmomentum.setPz( (Qplus-Qminus)/2 );
    Qmomentum.setE(  (Qplus+Qminus)/2 );
  }
  else if((Pprojectile+Qmomentum).mag2() <  ProjectileDiffCut2)   // Uzhi Target diffraction
  {
    G4double PPlusNew=SqrtS-TPlusNew;
    Qplus=PPlusNew-Pprojectile.plus();
    PMinusNew=ProjMassT2/PPlusNew;
    Qminus=PMinusNew-Pprojectile.minus();

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

  Pprojectile += Qmomentum;
  Ptarget     -= Qmomentum;

  // Vova

  /*
  Pprojectile.setPz(0.);
  Pprojectile.setE(SqrtS-M0target);
  Ptarget.setPz(0.);
  Ptarget.setE(M0target);
  */

  //G4cout << "Pprojectile with Q : " << Pprojectile << G4endl;
  //G4cout << "Ptarget with Q : " << Ptarget << G4endl;
  //G4cout << "Projectile back: " << toLab * Pprojectile << G4endl;
  //G4cout << "Target back: " << toLab * Ptarget << G4endl;

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

  //G4cout << "Pprojectile with Q M: " << Pprojectile<<" "<<  Pprojectile.mag() << G4endl;
  //G4cout << "Ptarget     with Q M: " << Ptarget    <<" "<<  Ptarget.mag()     << G4endl;
  //G4cout << "Target    mass  " <<  Ptarget.mag() << G4endl;

  target->Set4Momentum(Ptarget);

  //G4cout << "Projectile mass  " <<  Pprojectile.mag() << G4endl;

  projectile->Set4Momentum(Pprojectile);

  return true;
}


G4ExcitedString * G4QGSDiffractiveExcitation::
String(G4VSplitableHadron * hadron, G4bool isProjectile) const
{
  hadron->SplitUp();
  G4Parton *start= hadron->GetNextParton();
  if ( start==NULL) { 
    G4cout << " G4FTFModel::String() Error:No start parton found"<< G4endl;
    return NULL;
  }
  G4Parton *end  = hadron->GetNextParton();
  if ( end==NULL) { 
    G4cout << " G4FTFModel::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 ptSquared= hadron->Get4Momentum().perp2();
  G4double transverseMassSquared= hadron->Get4Momentum().plus()
                * hadron->Get4Momentum().minus();

  G4double maxAvailMomentumSquared=
    sqr( std::sqrt(transverseMassSquared) - std::sqrt(ptSquared) );

  G4double widthOfPtSquare = 0.25;          // Uzhi <Pt^2>=0.25 ???
  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 G4_FTFDEBUG
  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;
  /*
  do {
    x=Xmin + G4UniformRand() * range;
  }  while ( Xmin/x < G4UniformRand() );
  */

  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;
  /*
  do {
    pt2=widthSquare * G4Log( G4UniformRand() );
  } while ( pt2 > maxPtSquare);
  */

  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.);    
}