G4LundStringFragmentation.cc

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//
// -----------------------------------------------------------------------------
//      GEANT 4 class implementation file
//
//      History: first implementation, Maxim Komogorov, 10-Jul-1998
// -----------------------------------------------------------------------------
#include "G4LundStringFragmentation.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"
#include "G4FragmentingString.hh"
#include "G4DiQuarks.hh"
#include "G4Quarks.hh"

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

//#define debug_LUNDfragmentation

// Class G4LundStringFragmentation 
//*************************************************************************************

G4LundStringFragmentation::G4LundStringFragmentation()
{
    SetMassCut(210.*MeV);   //  Mpi + Delta
                            // For ProduceOneHadron it is required
                            // that no one pi-meson can be produced.

    SigmaQT = 0.435 * GeV;

    SetStringTensionParameter(1.*GeV/fermi);
    SetDiquarkBreakProbability(0.5);
    SetStrangenessSuppression((1.0 - 0.13)/2.0);

    SetDiquarkSuppression(0.15);

    // For the time being, set to 0.0 the probabilities for c-cbar and b-bbar creation.
    SetProbCCbar(0.0);  //(0.005);   // According to O.I. Piskunova Yad. Fiz. 56 (1993) 1094
    SetProbBBbar(0.0);  //(5.0e-5);  // According to O.I. Piskunova Yad. Fiz. 56 (1993) 1094

    SetMinMasses();  // For treating of small string decays
}

//--------------------------------------------------------------------------------------

G4KineticTrackVector* G4LundStringFragmentation::FragmentString(const G4ExcitedString& theString)
{
  // Can no longer modify Parameters for Fragmentation.

  PastInitPhase=true;

  G4FragmentingString  aString(theString);
  SetMinimalStringMass(&aString);

        #ifdef debug_LUNDfragmentation
        G4cout<<G4endl<<"LUND StringFragmentation ------------------------------------"<<G4endl;
        G4cout<<G4endl<<"LUND StringFragm: String Mass "
                      <<theString.Get4Momentum().mag()<<G4endl
                      <<"4Mom "<<theString.Get4Momentum()<<G4endl
                      <<"------------------------------------"<<G4endl;
        G4cout<<"String ends Direct "<<theString.GetLeftParton()->GetPDGcode()<<" "
                                     <<theString.GetRightParton()->GetPDGcode()<<" "
                                     <<theString.GetDirection()<< G4endl;
        G4cout<<"Left  mom "<<theString.GetLeftParton()->Get4Momentum()<<G4endl;
        G4cout<<"Right mom "<<theString.GetRightParton()->Get4Momentum()<<G4endl<<G4endl;
        G4cout<<"Check for Fragmentation "<<G4endl;
        #endif

  G4KineticTrackVector * LeftVector(0);

  if (!aString.IsAFourQuarkString() && !IsItFragmentable(&aString))
  {
                #ifdef debug_LUNDfragmentation
                G4cout<<"Non fragmentable - the string is converted to one hadron "<<G4endl;
                #endif
                // SetMassCut(210.*MeV);  // For ProduceOneHadron it is required
                                          // that no one pi-meson can be produced.

    G4double Mcut = GetMassCut();
    SetMassCut(10000.*MeV);
    LeftVector=ProduceOneHadron(&theString);
    SetMassCut(Mcut);

    LeftVector->operator[](0)->SetFormationTime(theString.GetTimeOfCreation());
    LeftVector->operator[](0)->SetPosition(theString.GetPosition());

    if (LeftVector->size() > 1)
                {
            // 2 hadrons created from qq-qqbar are stored
      LeftVector->operator[](1)->SetFormationTime(theString.GetTimeOfCreation());
      LeftVector->operator[](1)->SetPosition(theString.GetPosition());
    }
    return LeftVector;
  }

        #ifdef debug_LUNDfragmentation
        G4cout<<"The string will be fragmented. "<<G4endl;
        #endif

  // The string can fragment. At least two particles can be produced.
             LeftVector =new G4KineticTrackVector;
  G4KineticTrackVector * RightVector=new G4KineticTrackVector;

        G4bool success = Loop_toFragmentString(theString, LeftVector, RightVector);

  if ( ! success )
  {
    std::for_each(LeftVector->begin(), LeftVector->end(), DeleteKineticTrack());
    LeftVector->clear();
    std::for_each(RightVector->begin(), RightVector->end(), DeleteKineticTrack());
    delete RightVector;
    return LeftVector;
  }

  // Join Left- and RightVector into LeftVector in correct order.
  while (!RightVector->empty())
  {
    LeftVector->push_back(RightVector->back());
    RightVector->erase(RightVector->end()-1);
  }
  delete RightVector;

  return LeftVector;
}

//----------------------------------------------------------------------------------

G4bool G4LundStringFragmentation::IsItFragmentable(const G4FragmentingString * const string)
{
  SetMinimalStringMass(string);
        //G4cout<<"MinM StrM "<<MinimalStringMass<<" "<< string->Get4Momentum().mag()<<G4endl;

  return std::abs(MinimalStringMass) < string->Get4Momentum().mag();

        //MinimalStringMass is negative and large for a string with unknown particles in a final 2-particle decay.
}

//----------------------------------------------------------------------------------------

G4bool G4LundStringFragmentation::Loop_toFragmentString( const G4ExcitedString  &theString,
                                                         G4KineticTrackVector * & LeftVector,
                                                         G4KineticTrackVector * & RightVector )
{
        #ifdef debug_LUNDfragmentation
        G4cout<<"Loop_toFrag "<<theString.GetLeftParton()->GetPDGcode()<<" "
                              <<theString.GetLeftParton()->Get4Momentum()<<G4endl
              <<"            "<<theString.GetRightParton()->GetPDGcode()<<" "
                              <<theString.GetRightParton()->Get4Momentum()<<G4endl
              <<"Direction   "<<theString.GetDirection()<< G4endl;
        #endif

  G4bool final_success=false;
  G4bool inner_success=true;

  G4int attempt=0;

  while ( ! final_success && attempt++ < StringLoopInterrupt )
  {       // If the string fragmentation does not be happend, 
          // repeat the fragmentation.

    G4FragmentingString *currentString=new G4FragmentingString(theString);
    G4LorentzRotation toCms, toObserverFrame;

    //G4cout<<"Main loop start whilecounter "<<attempt<<G4endl;

    // Cleaning up the previously produced hadrons
    std::for_each(LeftVector->begin(), LeftVector->end(), DeleteKineticTrack());
    LeftVector->clear();
    std::for_each(RightVector->begin(), RightVector->end(), DeleteKineticTrack());
    RightVector->clear();

    // Main fragmentation loop until the string will not be able to fragment
    inner_success=true;  // set false on failure.
                const G4int maxNumberOfLoops = 1000;
                G4int loopCounter = -1;

    while ( (! StopFragmenting(currentString)) && ++loopCounter < maxNumberOfLoops )
    {       // Split current string into hadron + new string
                        #ifdef debug_LUNDfragmentation
                        G4cout<<"The string will fragment. "<<G4endl;;
                        //G4cout<<"1 "<<currentString->GetDecayDirection()<<G4endl;
                        #endif
      G4FragmentingString *newString=0;  // used as output from SplitUp.

      toCms=currentString->TransformToAlignedCms();
                        toObserverFrame= toCms.inverse();
                        #ifdef debug_LUNDfragmentation
                        //G4cout<<"CMS Left  mom "<<currentString->GetPleft()<<G4endl;
                        //G4cout<<"CMS Right mom "<<currentString->GetPright()<<G4endl;
                        //G4cout<<"CMS String M  "<<currentString->GetPstring()<<G4endl;
                        #endif

      G4KineticTrack * Hadron=Splitup(currentString,newString);

      if ( Hadron != 0 )  // Store the hadron                               
      {
                                #ifdef debug_LUNDfragmentation
                                G4cout<<"Hadron prod at fragm. "<<Hadron->GetDefinition()->GetParticleName()<<G4endl;
                                //G4cout<<"2 "<<currentString->GetDecayDirection()<<G4endl;
                                #endif

        Hadron->Set4Momentum(toObserverFrame*Hadron->Get4Momentum());

        G4double TimeOftheStringCreation=theString.GetTimeOfCreation();
        G4ThreeVector PositionOftheStringCreation(theString.GetPosition());

        G4LorentzVector Coordinate(Hadron->GetPosition(), Hadron->GetFormationTime());
        G4LorentzVector Momentum = toObserverFrame*Coordinate;
        Hadron->SetFormationTime(TimeOftheStringCreation + Momentum.e() - fermi/c_light);
        G4ThreeVector aPosition(Momentum.vect());
        Hadron->SetPosition(PositionOftheStringCreation+aPosition);
 
                                // Open to protect hadron production at fragmentation 
        if ( currentString->GetDecayDirection() > 0 )
                                {
          LeftVector->push_back(Hadron); 
                                } else
                                {
          RightVector->push_back(Hadron);
                                }
        delete currentString;
        currentString=newString;
      } else {
                          if ( newString ) delete newString;
                        }

                    currentString->LorentzRotate(toObserverFrame);
    };

                if ( loopCounter >= maxNumberOfLoops ) {
                  inner_success=false;
                }

    // Split remaining string into 2 final hadrons.
                #ifdef debug_LUNDfragmentation
                if (inner_success) G4cout<<"Split remaining string into 2 final hadrons."<<G4endl;
                #endif
    if ( inner_success && SplitLast(currentString, LeftVector, RightVector) )  // Close to protect Last Str. Decay
    {
      final_success = true;
    }

    delete currentString;
  }  // End of the loop where we try to fragment the string.
  return final_success;
}

//----------------------------------------------------------------------------------------

G4bool G4LundStringFragmentation::StopFragmenting(const G4FragmentingString * const string)
{
  SetMinimalStringMass(string); 

  if ( MinimalStringMass < 0.) return true;

  if (string->IsAFourQuarkString())
  {
    return G4UniformRand() < G4Exp(-0.0005*(string->Mass() - MinimalStringMass));
  } else {
           
                if (MinimalStringMass < 0.0 ) return false;  // For a string with di-quark having c or b quarks and s, c, b quarks

    G4bool Result = G4UniformRand() < 
        G4Exp(-0.66e-6*(string->Mass()*string->Mass() - MinimalStringMass*MinimalStringMass));
                // G4bool Result = string->Mass() < MinimalStringMass + 150.*MeV*G4UniformRand();     // a'la LUND

                #ifdef debug_LUNDfragmentation 
                G4cout<<"StopFragmenting MinimalStringMass string->Mass() "<<MinimalStringMass
                      <<" "<<string->Mass()<<G4endl;
                G4cout<<"StopFragmenting - Yes/No "<<Result<<G4endl;
                #endif  
    return Result;
  }
}

//-----------------------------------------------------------------------------

G4KineticTrack * G4LundStringFragmentation::Splitup(G4FragmentingString *string, 
                                  G4FragmentingString *&newString)
{
       #ifdef debug_LUNDfragmentation
       G4cout<<G4endl;
       G4cout<<"Start SplitUP ========================="<<G4endl;
       G4cout<<"String partons: " <<string->GetLeftParton()->GetPDGEncoding()<<" "
                                  <<string->GetRightParton()->GetPDGEncoding()<<" "
             <<"Direction "       <<string->GetDecayDirection()<<G4endl;
       #endif

       //... random choice of string end to use for creating the hadron (decay)   
       G4int SideOfDecay = (G4UniformRand() < 0.5)? 1: -1;
       if (SideOfDecay < 0)
       {
    string->SetLeftPartonStable();
       } else
       {
          string->SetRightPartonStable();
       }

       G4ParticleDefinition *newStringEnd;
       G4ParticleDefinition * HadronDefinition;

       G4double StringMass=string->Mass();

       G4double ProbDqADq = GetDiquarkSuppress();
       G4double ProbSaS   = 1.0 - 2.0 * GetStrangeSuppress();

       #ifdef debug_LUNDfragmentation
       G4cout<<"StrMass DiquarkSuppression           "<<StringMass<<" "<<GetDiquarkSuppress()<<G4endl; 
       #endif   

       G4int NumberOfpossibleBaryons = 2;

       if (string->GetLeftParton()->GetParticleSubType()  != "quark") NumberOfpossibleBaryons++; 
       if (string->GetRightParton()->GetParticleSubType() != "quark") NumberOfpossibleBaryons++;

       G4double ActualProb  = ProbDqADq ;
       ActualProb *= (1.0-sqr(NumberOfpossibleBaryons*1400.0/StringMass));

       SetDiquarkSuppression(ActualProb); 

       G4double Mth = 1250.0;                                  // 2 Mk + Mpi
       if ( NumberOfpossibleBaryons == 3 ){Mth = 2520.0;}       // Mlambda/Msigma + Mk + Mpi
       else if ( NumberOfpossibleBaryons == 4 ){Mth = 2380.0;}  // 2 Mlambda/Msigma + Mk + Mpi
       else {}

       ActualProb = ProbSaS * (1.0 - G4Pow::GetInstance()->powA( Mth/StringMass , 4.0 ));  
       if ( ActualProb < 0.0 ) ActualProb = 0.0;
       SetStrangenessSuppression((1.0-ActualProb)/2.0);

       #ifdef debug_LUNDfragmentation
       G4cout<<"StrMass DiquarkSuppression corrected "<<StringMass<<" "<<GetDiquarkSuppress()<<G4endl; 
       #endif

       if (string->DecayIsQuark())
       {
          HadronDefinition= QuarkSplitup(string->GetDecayParton(), newStringEnd);
       } else {
          HadronDefinition= DiQuarkSplitup(string->GetDecayParton(), newStringEnd);
       }

       SetDiquarkSuppression(ProbDqADq);
       SetStrangenessSuppression((1.0-ProbSaS)/2.0);

       if ( HadronDefinition == NULL ) { G4KineticTrack * Hadron =0; return Hadron; }

       #ifdef debug_LUNDfragmentation
       G4cout<<"The parton "<<string->GetDecayParton()->GetPDGEncoding()<<" "
             <<" produces hadron "<<HadronDefinition->GetParticleName()
             <<" and is transformed to "<<newStringEnd->GetPDGEncoding()<<G4endl;
       G4cout<<"The side of the string decay Left/Right (1/-1) "<<SideOfDecay<<G4endl;
       #endif
       // create new String from old, ie. keep Left and Right order, but replace decay

       if ( newString ) delete newString;

       newString=new G4FragmentingString(*string,newStringEnd);  // To store possible quark containt of new string

       #ifdef debug_LUNDfragmentation
       G4cout<<"An attempt to determine its energy (SplitEandP)"<<G4endl;
       #endif
       G4LorentzVector* HadronMomentum=SplitEandP(HadronDefinition, string, newString);

       delete newString; newString=0;
  
       G4KineticTrack * Hadron =0;
       if ( HadronMomentum != 0 ) {

           #ifdef debug_LUNDfragmentation
           G4cout<<"The attempt was successful"<<G4endl;
           #endif
     G4ThreeVector   Pos;
     Hadron = new G4KineticTrack(HadronDefinition, 0,Pos, *HadronMomentum);

           if ( newString ) delete newString;

     newString=new G4FragmentingString(*string,newStringEnd,
            HadronMomentum);
     delete HadronMomentum;
       }
       else
       {
           #ifdef debug_LUNDfragmentation
           G4cout<<"The attempt was not successful !!!"<<G4endl;
           #endif
       }

       #ifdef debug_LUNDfragmentation
       G4cout<<"End SplitUP (G4VLongitudinalStringDecay) ====================="<<G4endl;
       #endif

       return Hadron;
}

//-----------------------------------------------------------------------------

G4ParticleDefinition * G4LundStringFragmentation::DiQuarkSplitup(G4ParticleDefinition* decay,
                                                                 G4ParticleDefinition *&created)
{
   G4double StrSup=GetStrangeSuppress();
   G4double ProbQQbar = (1.0 - 2.0*StrSup);

   //... can Diquark break or not?
   if (G4UniformRand() < DiquarkBreakProb ){

      //... Diquark break
      G4int stableQuarkEncoding = decay->GetPDGEncoding()/1000;
      G4int decayQuarkEncoding = (decay->GetPDGEncoding()/100)%10;
      if (G4UniformRand() < 0.5)
      {
         G4int Swap = stableQuarkEncoding;
         stableQuarkEncoding = decayQuarkEncoding;
         decayQuarkEncoding = Swap;
      }

      G4int IsParticle=(decayQuarkEncoding>0) ? -1 : +1;  // if we have a quark, we need antiquark)

      pDefPair QuarkPair = CreatePartonPair(IsParticle,false);  // no diquarks wanted

      //... Build new Diquark
      G4int QuarkEncoding=QuarkPair.second->GetPDGEncoding();
      G4int i10  = std::max(std::abs(QuarkEncoding), std::abs(stableQuarkEncoding));
      G4int i20  = std::min(std::abs(QuarkEncoding), std::abs(stableQuarkEncoding));
      G4int spin = (i10 != i20 && G4UniformRand() <= 0.5)? 1 : 3;
      G4int NewDecayEncoding = -1*IsParticle*(i10 * 1000 + i20 * 100 + spin);
      created = FindParticle(NewDecayEncoding);
      G4ParticleDefinition * decayQuark=FindParticle(decayQuarkEncoding);
      G4ParticleDefinition * had=hadronizer->Build(QuarkPair.first, decayQuark);
      StrangeSuppress=StrSup;

      return had;

   } else {
      //... Diquark does not break

      G4int IsParticle=(decay->GetPDGEncoding()>0) ? +1 : -1;  // if we have a diquark, we need quark

      StrangeSuppress=(1.0 - ProbQQbar * 0.9)/2.0;
      pDefPair QuarkPair = CreatePartonPair(IsParticle,false);  // no diquarks wanted

      created = QuarkPair.second;

      G4ParticleDefinition * had=hadronizer->Build(QuarkPair.first, decay);
      StrangeSuppress=StrSup;

      return had;
   }
}

//-----------------------------------------------------------------------------

G4LorentzVector * G4LundStringFragmentation::SplitEandP(G4ParticleDefinition * pHadron,
                                                        G4FragmentingString *   string, 
                                                        G4FragmentingString * newString)
{ 
  G4LorentzVector String4Momentum=string->Get4Momentum();
  G4double StringMT2=string->MassT2();
  G4double StringMT =std::sqrt(StringMT2);

  G4double HadronMass = pHadron->GetPDGMass();
  SetMinimalStringMass(newString);

       if ( MinimalStringMass < 0.0 ) return nullptr;

        #ifdef debug_LUNDfragmentation
        G4cout<<G4endl<<"Start LUND SplitEandP "<<G4endl;
        G4cout<<"String 4 mom, String M and Mt "<<String4Momentum<<" "<<String4Momentum.mag()
              <<" "<<std::sqrt(StringMT2)<<G4endl;
        G4cout<<"Hadron "<<pHadron->GetParticleName()<<G4endl;
        G4cout<<"HadM MinimalStringMassLeft StringM hM+sM "<<HadronMass<<" "<<MinimalStringMass<<" "
              <<String4Momentum.mag()<<" "<<HadronMass+MinimalStringMass<<G4endl;
        #endif

  if ((HadronMass + MinimalStringMass > string->Mass()) || MinimalStringMass < 0.) 
  {
          #ifdef debug_LUNDfragmentation
          G4cout<<"Mass of the string is not sufficient to produce the hadron!"<<G4endl;
          #endif
    return 0;
  }  // have to start all over!

  String4Momentum.setPz(0.);
  G4ThreeVector StringPt=String4Momentum.vect();

  // calculate and assign hadron transverse momentum component HadronPx and HadronPy
  G4ThreeVector HadronPt    , RemSysPt; 
  G4double      HadronMassT2, ResidualMassT2;
  G4double HadronMt, Pt, Pt2, phi;
        //...  sample Pt of the hadron
        G4int attempt=0;
        do
        {
          attempt++; if (attempt > StringLoopInterrupt) {return 0;}

    HadronMt = HadronMass - 300.0*G4Log(G4UniformRand());
    Pt2 = sqr(HadronMt)-sqr(HadronMass); Pt=std::sqrt(Pt2);
    phi = 2.*pi*G4UniformRand();
    G4ThreeVector SampleQuarkPtw= G4ThreeVector(Pt * std::cos(phi),Pt * std::sin(phi),0);

          HadronPt =SampleQuarkPtw  + string->DecayPt();
          HadronPt.setZ(0);
          RemSysPt = StringPt - HadronPt;

          HadronMassT2 = sqr(HadronMass) + HadronPt.mag2();
          ResidualMassT2=sqr(MinimalStringMass) + RemSysPt.mag2();

        } while (std::sqrt(HadronMassT2) + std::sqrt(ResidualMassT2) > StringMT);

  //...  sample z to define hadron longitudinal momentum and energy
  //... but first check the available phase space

  G4double Pz2 = (sqr(StringMT2 - HadronMassT2 - ResidualMassT2) -
      4*HadronMassT2 * ResidualMassT2)/4./StringMT2;

  if (Pz2 < 0 ) {return 0;}          // have to start all over!

  //... then compute allowed z region  z_min <= z <= z_max

  G4double Pz = std::sqrt(Pz2);
  G4double zMin = (std::sqrt(HadronMassT2+Pz2) - Pz)/std::sqrt(StringMT2);
        // G4double zMin = (std::sqrt(HadronMassT2+Pz2) - 0.)/std::sqrt(StringMT2); // For testing purposes
  G4double zMax = (std::sqrt(HadronMassT2+Pz2) + Pz)/std::sqrt(StringMT2);

  if (zMin >= zMax) return 0;   // have to start all over!

  G4double z = GetLightConeZ(zMin, zMax, 
                 string->GetDecayParton()->GetPDGEncoding(), pHadron,
                 HadronPt.x(), HadronPt.y());

  //... now compute hadron longitudinal momentum and energy
  // longitudinal hadron momentum component HadronPz

  HadronPt.setZ(0.5* string->GetDecayDirection() *
           (z * string->LightConeDecay() - 
          HadronMassT2/(z * string->LightConeDecay())));
  G4double HadronE  = 0.5* (z * string->LightConeDecay() +
          HadronMassT2/(z * string->LightConeDecay()));

  G4LorentzVector * a4Momentum= new G4LorentzVector(HadronPt,HadronE);

        #ifdef debug_LUNDfragmentation
        G4cout<<G4endl<<" string->GetDecayDirection() "<<string->GetDecayDirection()<<G4endl<<G4endl;
        G4cout<<"string->LightConeDecay() "<<string->LightConeDecay()<<G4endl;
        G4cout<<"HadronPt,HadronE "<<HadronPt<<" "<<HadronE<<G4endl;
        G4cout<<"String4Momentum "<<String4Momentum<<G4endl;
        G4cout<<"Out of LUND SplitEandP "<<G4endl<<G4endl;
        #endif

  return a4Momentum;
}

//-----------------------------------------------------------------------------------------

G4double G4LundStringFragmentation::GetLightConeZ(G4double zmin, G4double zmax, 
                                      G4int PDGEncodingOfDecayParton,
                                      G4ParticleDefinition* pHadron,
                                      G4double Px, G4double Py)
{
  G4double Mass = pHadron->GetPDGMass();
        G4int HadronEncoding=std::abs(pHadron->GetPDGEncoding());

  G4double Mt2 = Px*Px + Py*Py + Mass*Mass;

  G4double  Alund, Blund;
  G4double zOfMaxyf(0.), maxYf(1.), z(0.), yf(1.);

  if (!((std::abs(PDGEncodingOfDecayParton) > 1000) && (HadronEncoding > 1000)) )
  {    // ---------------- Quark fragmentation  and qq-> meson ----------------------
           Alund=1.;
           Blund=0.7/GeV/GeV;

     G4double BMt2 = Blund*Mt2;
     if (Alund == 1.0) {
       zOfMaxyf=BMt2/(Blund*Mt2 + 1.);}
     else {  
         zOfMaxyf = ((1.0+BMt2) - std::sqrt(sqr(1.0-BMt2) + 4.0*BMt2*Alund))/2.0/(1.-Alund);
     }

     if (zOfMaxyf < zmin) {zOfMaxyf=zmin;}
     if (zOfMaxyf > zmax) {zOfMaxyf=zmax;}
     maxYf=(1-zOfMaxyf)/zOfMaxyf * G4Exp(-Blund*Mt2/zOfMaxyf);

           const G4int maxNumberOfLoops = 1000;
           G4int loopCounter = 0;
     do
     {
    z = zmin + G4UniformRand()*(zmax-zmin);
                //yf = (1-z)/z * G4Exp(-Blund*Mt2/z);
    yf = G4Pow::GetInstance()->powA(1.0-z,Alund)/z*G4Exp(-BMt2/z);
     }
     while ( (G4UniformRand()*maxYf > yf) && ++loopCounter < maxNumberOfLoops );
           if ( loopCounter >= maxNumberOfLoops ) {
             z = 0.5*(zmin + zmax);  // Just a value between zmin and zmax, no physics considerations at all! 
           }
     return z;
        }

  if (std::abs(PDGEncodingOfDecayParton) > 1000)     
  {
    G4double an = 2.5; 
    an +=(sqr(Px)+sqr(Py))/sqr(GeV)-0.5;
    z=zmin + (zmax-zmin)*G4Pow::GetInstance()->powA(G4UniformRand(),1./an);
  }

  return z;
}

//----------------------------------------------------------------------------------------------------------

G4bool G4LundStringFragmentation::SplitLast(G4FragmentingString * string,
                                            G4KineticTrackVector * LeftVector,
                                            G4KineticTrackVector * RightVector)
{
  //... perform last cluster decay
        SetMinimalStringMass( string);
        if ( MinimalStringMass < 0.) return false;
        #ifdef debug_LUNDfragmentation
        G4cout<<G4endl<<"Split last-----------------------------------------"<<G4endl;
        G4cout<<"MinimalStringMass "<<MinimalStringMass<<G4endl;
        G4cout<<"Left  "<<string->GetLeftParton()->GetPDGEncoding()<<" "<<string->GetPleft()<<G4endl;
        G4cout<<"Right "<<string->GetRightParton()->GetPDGEncoding()<<" "<<string->GetPright()<<G4endl;
        G4cout<<"String4mom "<<string->GetPstring()<<" "<<string->GetPstring().mag()<<G4endl;
        #endif

  G4LorentzVector Str4Mom=string->Get4Momentum();

  G4LorentzRotation toCms=string->TransformToAlignedCms();                                  
  G4LorentzRotation toObserverFrame= toCms.inverse();

  G4double StringMass=string->Mass();

  G4ParticleDefinition * LeftHadron(0), * RightHadron(0);

        NumberOf_FS=0;
  for (G4int i=0; i<350; i++) {FS_Weight[i]=0.;}

  G4int sampledState = 0;

        #ifdef debug_LUNDfragmentation
        G4cout<<"StrMass "<<StringMass<<" q's "
              <<string->GetLeftParton()->GetParticleName()<<" "
              <<string->GetRightParton()->GetParticleName()<<G4endl;
        #endif

  string->SetLeftPartonStable(); // to query quark contents..

  if (string->IsAFourQuarkString() )
  {
    // The string is qq-qqbar type. Diquarks are on the string ends
          if (StringMass-MinimalStringMass < 0.)
    {
      if (! Diquark_AntiDiquark_belowThreshold_lastSplitting(string, LeftHadron, RightHadron) )
                        {
        return false;
                        }
    } else
    {
      Diquark_AntiDiquark_aboveThreshold_lastSplitting(string, LeftHadron, RightHadron);

      if (NumberOf_FS == 0) return false;

                        sampledState = SampleState();
      if (string->GetLeftParton()->GetPDGEncoding() < 0)
      {
        LeftHadron =FS_LeftHadron[sampledState];
        RightHadron=FS_RightHadron[sampledState];
      } else
      {
        LeftHadron =FS_RightHadron[sampledState];
        RightHadron=FS_LeftHadron[sampledState];
      }
    }
        } else
  {
    if (string->DecayIsQuark() && string->StableIsQuark() )
    {       //... there are quarks on cluster ends
                        #ifdef debug_LUNDfragmentation
                        G4cout<<"Q Q string LastSplit"<<G4endl;
                        #endif
      Quark_AntiQuark_lastSplitting(string, LeftHadron, RightHadron);
    
      if (NumberOf_FS == 0) return false;
                  sampledState = SampleState();
      if (string->GetLeftParton()->GetPDGEncoding() < 0)
      {
        LeftHadron =FS_RightHadron[sampledState];
        RightHadron=FS_LeftHadron[sampledState];
      } else
      {
        LeftHadron =FS_LeftHadron[sampledState];
        RightHadron=FS_RightHadron[sampledState];
      }
    } else 
    {       //... there is a Diquark on one of the cluster ends
                        #ifdef debug_LUNDfragmentation
                        G4cout<<"DiQ Q string Last Split"<<G4endl;
                        #endif

      Quark_Diquark_lastSplitting(string, LeftHadron, RightHadron);

      if (NumberOf_FS == 0) return false;                           
                  sampledState = SampleState();

      if (string->GetLeftParton()->GetParticleSubType() == "quark")
      {
        LeftHadron =FS_LeftHadron[sampledState];
        RightHadron=FS_RightHadron[sampledState];
      } else 
      {
        LeftHadron =FS_RightHadron[sampledState];
        RightHadron=FS_LeftHadron[sampledState];
      }     
    }

  }

        #ifdef debug_LUNDfragmentation
        G4cout<<"Sampled hadrons: "<<LeftHadron->GetParticleName()<<" "<<RightHadron->GetParticleName()<<G4endl;
        #endif

  G4LorentzVector P_left  =string->GetPleft(), P_right = string->GetPright();

  G4LorentzVector  LeftMom, RightMom;
  G4ThreeVector    Pos;

  Sample4Momentum(&LeftMom,  LeftHadron->GetPDGMass(),
      &RightMom, RightHadron->GetPDGMass(),
      StringMass);

        // Sample4Momentum ascribes LeftMom.pz() along positive Z axis for baryons in many cases.
        // It must be negative in case when the system is moving against Z axis.

  if (!(string->DecayIsQuark() && string->StableIsQuark() ))
  { // Only for qq - q, q - qq, and qq - qqbar -------------------

    if (std::abs(string->GetLeftParton()->GetPDGEncoding()) > 1000) 
    {
      if (P_left.z() <= 0.) {G4LorentzVector tmp = LeftMom; LeftMom=RightMom; RightMom=tmp;}
    } 
    else  
    {
      if (P_right.z() >= 0.) {G4LorentzVector tmp = LeftMom; LeftMom=RightMom; RightMom=tmp;}
    }
  }

  LeftMom *=toObserverFrame;
  RightMom*=toObserverFrame;

  LeftVector->push_back(new G4KineticTrack(LeftHadron, 0, Pos, LeftMom));
  RightVector->push_back(new G4KineticTrack(RightHadron, 0, Pos, RightMom));

  string->LorentzRotate(toObserverFrame);
  return true;
}

//----------------------------------------------------------------------------------------

G4bool G4LundStringFragmentation::
Diquark_AntiDiquark_belowThreshold_lastSplitting(G4FragmentingString * & string,
                                                 G4ParticleDefinition * & LeftHadron,
                                                 G4ParticleDefinition * & RightHadron)
{
  G4double StringMass   = string->Mass();

        G4bool isOK = false;
  G4int cClusterInterrupt = 0;
  do
  {
    G4int LeftQuark1= string->GetLeftParton()->GetPDGEncoding()/1000;
    G4int LeftQuark2=(string->GetLeftParton()->GetPDGEncoding()/100)%10;

    G4int RightQuark1= string->GetRightParton()->GetPDGEncoding()/1000;
    G4int RightQuark2=(string->GetRightParton()->GetPDGEncoding()/100)%10;

    if (G4UniformRand()<0.5)
    {
      LeftHadron =hadronizer->Build(FindParticle( LeftQuark1),
                  FindParticle(RightQuark1));
            RightHadron= (LeftHadron == nullptr) ? nullptr :
                        hadronizer->Build(FindParticle( LeftQuark2),
                              FindParticle(RightQuark2));
          } else
          {
                  LeftHadron =hadronizer->Build(FindParticle( LeftQuark1),
                        FindParticle(RightQuark2));
                  RightHadron=(LeftHadron == nullptr) ? nullptr :
                        hadronizer->Build(FindParticle( LeftQuark2),
                              FindParticle(RightQuark1));
          }

          isOK = (LeftHadron != nullptr) && (RightHadron != nullptr);
          if(isOK) { isOK = (StringMass > LeftHadron->GetPDGMass() + RightHadron->GetPDGMass()); }
          ++cClusterInterrupt;
          //... repeat procedure, if mass of cluster is too low to produce hadrons
          //... ClusterMassCut = 0.15*GeV model parameter                                                                                                 
        }
        while (isOK == false || cClusterInterrupt < ClusterLoopInterrupt);
        /* Loop checking, 07.08.2015, A.Ribon */
    return isOK;
}

//----------------------------------------------------------------------------------------

G4bool G4LundStringFragmentation::
Diquark_AntiDiquark_aboveThreshold_lastSplitting(G4FragmentingString * & string,
                                                 G4ParticleDefinition * & LeftHadron,
                                                 G4ParticleDefinition * & RightHadron)
{
  // StringMass-MinimalStringMass > 0. Creation of 2 baryons is possible ----

  G4double StringMass   = string->Mass();
  G4double StringMassSqr= sqr(StringMass); 
  G4ParticleDefinition * Di_Quark;
  G4ParticleDefinition * Anti_Di_Quark;

  if (string->GetLeftParton()->GetPDGEncoding() < 0)
  {
    Anti_Di_Quark   =string->GetLeftParton();
    Di_Quark=string->GetRightParton();
  } else
  {
    Anti_Di_Quark   =string->GetRightParton();
    Di_Quark=string->GetLeftParton();
  }

  G4int IDAnti_di_quark    =Anti_Di_Quark->GetPDGEncoding();
  G4int AbsIDAnti_di_quark =std::abs(IDAnti_di_quark);
  G4int IDdi_quark         =Di_Quark->GetPDGEncoding();
  G4int AbsIDdi_quark      =std::abs(IDdi_quark);

  G4int ADi_q1=AbsIDAnti_di_quark/1000;
  G4int ADi_q2=(AbsIDAnti_di_quark-ADi_q1*1000)/100;

  G4int Di_q1=AbsIDdi_quark/1000;
  G4int Di_q2=(AbsIDdi_quark-Di_q1*1000)/100;

  NumberOf_FS=0;
  for (G4int ProdQ=1; ProdQ < 6; ProdQ++)
  {
    G4int StateADiQ=0;
                const G4int maxNumberOfLoops = 1000;
                G4int loopCounter = 0;
    do  // while(Meson[AbsIDquark-1][ProdQ-1][StateQ]<>0);
    {
      LeftHadron=G4ParticleTable::GetParticleTable()->FindParticle(
              -Baryon[ADi_q1-1][ADi_q2-1][ProdQ-1][StateADiQ]);

      if (LeftHadron == NULL) continue;
      G4double LeftHadronMass=LeftHadron->GetPDGMass();

      G4int StateDiQ=0;
                        const G4int maxNumberOfInternalLoops = 1000;
                        G4int internalLoopCounter = 0;
      do // while(Baryon[Di_q1-1][Di_q2-1][ProdQ-1][StateDiQ]<>0);
      {
        RightHadron=G4ParticleTable::GetParticleTable()->FindParticle(
                +Baryon[Di_q1-1][Di_q2-1][ProdQ-1][StateDiQ]);

        if (RightHadron == NULL) continue;
        G4double RightHadronMass=RightHadron->GetPDGMass();

        if (StringMass > LeftHadronMass + RightHadronMass)
        {
                                        if ( NumberOf_FS > 349 ) {
                                          G4ExceptionDescription ed;
                                          ed << " NumberOf_FS exceeds its limit: NumberOf_FS=" << NumberOf_FS << G4endl;
                                          G4Exception( "G4LundStringFragmentation::Diquark_AntiDiquark_aboveThreshold_lastSplitting ",
                                                       "HAD_LUND_001", JustWarning, ed );
                                          NumberOf_FS = 349;
                                        }

          G4double FS_Psqr=lambda(StringMassSqr,sqr(LeftHadronMass),
                sqr(RightHadronMass));
          //FS_Psqr=1.;
          FS_Weight[NumberOf_FS]=std::sqrt(FS_Psqr)*FS_Psqr*
                     BaryonWeight[ADi_q1-1][ADi_q2-1][ProdQ-1][StateADiQ]*
                     BaryonWeight[Di_q1-1][Di_q2-1][ProdQ-1][StateDiQ]*
                     Prob_QQbar[ProdQ-1];

          FS_LeftHadron[NumberOf_FS] = LeftHadron;
          FS_RightHadron[NumberOf_FS]= RightHadron;
          NumberOf_FS++;
        } // End of if (StringMass > LeftHadronMass + RightHadronMass)

        StateDiQ++;

      } while( (Baryon[Di_q1-1][Di_q2-1][ProdQ-1][StateDiQ]!=0) && 
                                 ++internalLoopCounter < maxNumberOfInternalLoops );
                        if ( internalLoopCounter >= maxNumberOfInternalLoops ) {
                          return false;
                        }
 
      StateADiQ++;
    } while( (Baryon[ADi_q1-1][ADi_q2-1][ProdQ-1][StateADiQ]!=0) &&
                         ++loopCounter < maxNumberOfLoops ); 
                if ( loopCounter >= maxNumberOfLoops ) {
                  return false;
                }
  } // End of for (G4int ProdQ=1; ProdQ < 4; ProdQ++)

    return true;
}

//----------------------------------------------------------------------------------------

G4bool G4LundStringFragmentation::Quark_Diquark_lastSplitting(G4FragmentingString * & string,
                                                              G4ParticleDefinition * & LeftHadron,
                                                              G4ParticleDefinition * & RightHadron)
{
  G4double StringMass   = string->Mass();
  G4double StringMassSqr= sqr(StringMass);

  G4ParticleDefinition * Di_Quark;
  G4ParticleDefinition * Quark;

  if (string->GetLeftParton()->GetParticleSubType()== "quark")
  {
    Quark   =string->GetLeftParton();
    Di_Quark=string->GetRightParton();
  } else
  {
    Quark   =string->GetRightParton();
    Di_Quark=string->GetLeftParton();
  }

  G4int IDquark        =Quark->GetPDGEncoding();
  G4int AbsIDquark     =std::abs(IDquark);
  G4int IDdi_quark   =Di_Quark->GetPDGEncoding();
  G4int AbsIDdi_quark=std::abs(IDdi_quark);
  G4int Di_q1=AbsIDdi_quark/1000;
  G4int Di_q2=(AbsIDdi_quark-Di_q1*1000)/100;

  G4int              SignDiQ= 1;
  if (IDdi_quark < 0) SignDiQ=-1;

  NumberOf_FS=0;
  for (G4int ProdQ=1; ProdQ < 4; ProdQ++)
  {
    G4int SignQ;
    if (IDquark > 0)
    {                                   SignQ=-1;
      if (IDquark == 2)                   SignQ= 1;
      if ((IDquark == 1) && (ProdQ == 3)) SignQ= 1; // K0
      if ((IDquark == 3) && (ProdQ == 1)) SignQ=-1; // K0bar
    } else
    {
      SignQ= 1;
      if (IDquark == -2)                  SignQ=-1;
      if ((IDquark ==-1) && (ProdQ == 3)) SignQ=-1; // K0bar
      if ((IDquark ==-3) && (ProdQ == 1)) SignQ= 1; // K0
    }

    if (AbsIDquark == ProdQ)            SignQ= 1;

    G4int StateQ=0;
                const G4int maxNumberOfLoops = 1000;
                G4int loopCounter = 0;
    do  // while(Meson[AbsIDquark-1][ProdQ-1][StateQ]<>0);
    {
      LeftHadron=G4ParticleTable::GetParticleTable()->FindParticle(SignQ*
              Meson[AbsIDquark-1][ProdQ-1][StateQ]);
      if (LeftHadron == NULL) continue;
      G4double LeftHadronMass=LeftHadron->GetPDGMass();

      G4int StateDiQ=0;
                        const G4int maxNumberOfInternalLoops = 1000;
                        G4int internalLoopCounter = 0;
      do // while(Baryon[Di_q1-1][Di_q2-1][ProdQ-1][StateDiQ]<>0);
      {
        RightHadron=G4ParticleTable::GetParticleTable()->FindParticle(SignDiQ*
                Baryon[Di_q1-1][Di_q2-1][ProdQ-1][StateDiQ]);
        if (RightHadron == NULL) continue;
        G4double RightHadronMass=RightHadron->GetPDGMass();

        if (StringMass > LeftHadronMass + RightHadronMass)
        {
                                        if ( NumberOf_FS > 349 ) {
                                          G4ExceptionDescription ed;
                                          ed << " NumberOf_FS exceeds its limit: NumberOf_FS=" << NumberOf_FS << G4endl;
                                          G4Exception( "G4LundStringFragmentation::Quark_Diquark_lastSplitting ",
                                                       "HAD_LUND_002", JustWarning, ed );
                                          NumberOf_FS = 349;
                                        }

          G4double FS_Psqr=lambda(StringMassSqr,sqr(LeftHadronMass),
                sqr(RightHadronMass));
          FS_Weight[NumberOf_FS]=std::sqrt(FS_Psqr)*
                     MesonWeight[AbsIDquark-1][ProdQ-1][StateQ]*
                     BaryonWeight[Di_q1-1][Di_q2-1][ProdQ-1][StateDiQ]*
                     Prob_QQbar[ProdQ-1];

          FS_LeftHadron[NumberOf_FS] = LeftHadron;
          FS_RightHadron[NumberOf_FS]= RightHadron;

          NumberOf_FS++;
        } // End of if (StringMass > LeftHadronMass + RightHadronMass)

        StateDiQ++;

      } while( (Baryon[Di_q1-1][Di_q2-1][ProdQ-1][StateDiQ]!=0) &&
                                 ++internalLoopCounter < maxNumberOfInternalLoops );
                        if ( internalLoopCounter >= maxNumberOfInternalLoops ) {
                          return false;
                        }

      StateQ++;
    } while( (Meson[AbsIDquark-1][ProdQ-1][StateQ]!=0) &&
                         ++loopCounter < maxNumberOfLoops );  /* Loop checking, 07.08.2015, A.Ribon */

                  if ( loopCounter >= maxNumberOfLoops ) {
                    return false;
                  }
  }

  return true;
}

//----------------------------------------------------------------------------------------

G4bool G4LundStringFragmentation::Quark_AntiQuark_lastSplitting(G4FragmentingString * & string,
                                                                G4ParticleDefinition * & LeftHadron,
                                                                G4ParticleDefinition * & RightHadron)
{
  G4double StringMass   = string->Mass();
  G4double StringMassSqr= sqr(StringMass);

  G4ParticleDefinition * Quark;
  G4ParticleDefinition * Anti_Quark;

  if (string->GetLeftParton()->GetPDGEncoding()>0)
  {
    Quark     =string->GetLeftParton();
    Anti_Quark=string->GetRightParton();
  } else
  {
    Quark     =string->GetRightParton();
    Anti_Quark=string->GetLeftParton();
  }

  G4int IDquark         =Quark->GetPDGEncoding();
  G4int AbsIDquark      =std::abs(IDquark);
        G4int QuarkCharge     =Qcharge[IDquark-1];

  G4int IDanti_quark    =Anti_Quark->GetPDGEncoding();
  G4int AbsIDanti_quark =std::abs(IDanti_quark);
        G4int AntiQuarkCharge =-Qcharge[AbsIDanti_quark-1];

        G4int LeftHadronCharge(0), RightHadronCharge(0);

        //G4cout<<"Q Qbar "<<IDquark<<" "<<IDanti_quark<<G4endl;

  NumberOf_FS=0;
  for (G4int ProdQ=1; ProdQ < 4; ProdQ++)
  {
    LeftHadronCharge = QuarkCharge - Qcharge[ProdQ-1];
    G4int SignQ = LeftHadronCharge/3; if (SignQ == 0) SignQ = 1;

    if ((IDquark == 1) && (ProdQ == 3)) SignQ= 1; // K0
    if ((IDquark == 3) && (ProdQ == 1)) SignQ=-1; // K0bar

                RightHadronCharge = AntiQuarkCharge + Qcharge[ProdQ-1];
    G4int SignAQ = RightHadronCharge/3; if (SignAQ == 0) SignAQ = 1;

    if ((IDanti_quark ==-1) && (ProdQ == 3)) SignAQ=-1; // K0bar
    if ((IDanti_quark ==-3) && (ProdQ == 1)) SignAQ= 1; // K0

                //G4cout<<"ProQ signs "<<ProdQ<<" "<<SignQ<<" "<<SignAQ<<G4endl;

    G4int StateQ=0;
                const G4int maxNumberOfLoops = 1000;
                G4int loopCounter = 0;
    do
    {
                        //G4cout<<"[AbsIDquark-1][ProdQ-1][StateQ "<<AbsIDquark-1<<" "
                        //<<ProdQ-1<<" "<<StateQ<<" "<<SignQ*Meson[AbsIDquark-1][ProdQ-1][StateQ]<<G4endl;
      LeftHadron=G4ParticleTable::GetParticleTable()->FindParticle(SignQ*
                   Meson[AbsIDquark-1][ProdQ-1][StateQ]);
                        //G4cout<<"LeftHadron "<<LeftHadron<<G4endl;
      if (LeftHadron == NULL) { StateQ++; continue; }
                        //G4cout<<"LeftHadron "<<LeftHadron->GetParticleName()<<G4endl;
      G4double LeftHadronMass=LeftHadron->GetPDGMass();

      G4int StateAQ=0;
                        const G4int maxNumberOfInternalLoops = 1000;
                        G4int internalLoopCounter = 0;
      do
      {
                                //G4cout<<"           [AbsIDanti_quark-1][ProdQ-1][StateAQ] "<<AbsIDanti_quark-1<<" "
                                //      <<ProdQ-1<<" "<<StateAQ<<" "<<SignAQ*Meson[AbsIDanti_quark-1][ProdQ-1][StateAQ]<<G4endl;
        RightHadron=G4ParticleTable::GetParticleTable()->FindParticle(SignAQ*
                Meson[AbsIDanti_quark-1][ProdQ-1][StateAQ]);
                                //G4cout<<"RightHadron "<<RightHadron<<G4endl;
        if(RightHadron == NULL) { StateAQ++; continue; }
                                //G4cout<<"RightHadron "<<RightHadron->GetParticleName()<<G4endl;
        G4double RightHadronMass=RightHadron->GetPDGMass();

        if (StringMass > LeftHadronMass + RightHadronMass)
        {
                                        if ( NumberOf_FS > 349 ) {
                                          G4ExceptionDescription ed;
                                          ed << " NumberOf_FS exceeds its limit: NumberOf_FS=" << NumberOf_FS << G4endl;
                                          G4Exception( "G4LundStringFragmentation::Quark_AntiQuark_lastSplitting ",
                                                       "HAD_LUND_003", JustWarning, ed );
                                          NumberOf_FS = 349;
                                        }

                                        G4double FS_Psqr=lambda(StringMassSqr,sqr(LeftHadronMass),
                sqr(RightHadronMass));
          //FS_Psqr=1.;
          FS_Weight[NumberOf_FS]=std::sqrt(FS_Psqr)*
                     MesonWeight[AbsIDquark-1][ProdQ-1][StateQ]*
                     MesonWeight[AbsIDanti_quark-1][ProdQ-1][StateAQ]*
                     Prob_QQbar[ProdQ-1];

          if (string->GetLeftParton()->GetPDGEncoding()>0)
          {
            FS_LeftHadron[NumberOf_FS] = RightHadron;
            FS_RightHadron[NumberOf_FS]= LeftHadron;
          } else
          {
            FS_LeftHadron[NumberOf_FS] = LeftHadron;
            FS_RightHadron[NumberOf_FS]= RightHadron;
          }

          NumberOf_FS++;

        }

        StateAQ++;
                                //G4cout<<"               StateAQ Meson[AbsIDanti_quark-1][ProdQ-1][StateAQ] "<<StateAQ<<" "
                                //      <<Meson[AbsIDanti_quark-1][ProdQ-1][StateAQ]<<" "<<internalLoopCounter<<G4endl;
      } while ( (Meson[AbsIDanti_quark-1][ProdQ-1][StateAQ]!=0) &&
                                  ++internalLoopCounter < maxNumberOfInternalLoops );
                          if ( internalLoopCounter >= maxNumberOfInternalLoops ) {
                            return false;
                          }

      StateQ++;
                        //G4cout<<"StateQ Meson[AbsIDquark-1][ProdQ-1][StateQ] "<<StateQ<<" "
                        //      <<Meson[AbsIDquark-1][ProdQ-1][StateQ]<<" "<<loopCounter<<G4endl;

    } while ( (Meson[AbsIDquark-1][ProdQ-1][StateQ]!=0) &&
                         ++loopCounter < maxNumberOfLoops );
                  if ( loopCounter >= maxNumberOfLoops ) {
                    return false;
                  }
  } // End of for (G4int ProdQ=1; ProdQ < 4; ProdQ++)

  return true;
}

//----------------------------------------------------------------------------------------------------------

G4int G4LundStringFragmentation::SampleState(void) 
{
        if ( NumberOf_FS > 349 ) {
          G4ExceptionDescription ed;
          ed << " NumberOf_FS exceeds its limit: NumberOf_FS=" << NumberOf_FS << G4endl;
          G4Exception( "G4LundStringFragmentation::SampleState ", "HAD_LUND_004", JustWarning, ed );
          NumberOf_FS = 349;
        }

  G4double SumWeights=0.;

  for (G4int i=0; i<NumberOf_FS; i++) {SumWeights+=FS_Weight[i];}

  G4double ksi=G4UniformRand();
  G4double Sum=0.;
  G4int indexPosition = 0;

  for (G4int i=0; i<NumberOf_FS; i++)
  {
    Sum+=(FS_Weight[i]/SumWeights);
    indexPosition=i;
    if (Sum >= ksi) break;
  }
  return indexPosition;
}

//----------------------------------------------------------------------------------------------------------

void G4LundStringFragmentation::Sample4Momentum(G4LorentzVector*     Mom, G4double     Mass, 
                                                G4LorentzVector* AntiMom, G4double AntiMass, 
                                                G4double InitialMass) 
{
  // ------ Sampling of momenta of 2 last produced hadrons --------------------
  G4ThreeVector Pt;
  G4double MassMt, AntiMassMt;
  G4double AvailablePz, AvailablePz2;
        #ifdef debug_LUNDfragmentation
        G4cout<<"Sampling of momenta of 2 last produced hadrons ----------------"<<G4endl;
        G4cout<<"Init Mass "<<InitialMass<<" FirstM "<<Mass<<" SecondM "<<AntiMass<<" ProbIsotropy "<<G4endl;  
        #endif

  G4double r_val = sqr(InitialMass*InitialMass - Mass*Mass - AntiMass*AntiMass) -   
      sqr(2.*Mass*AntiMass);
  G4double Pabs = (r_val > 0.)? std::sqrt(r_val)/(2.*InitialMass) : 0;

        const G4int maxNumberOfLoops = 1000;
  G4double SigmaQTw=SigmaQT;
  if (Mass > 930. || AntiMass > 930.) SigmaQT *=(1.0-0.55*sqr((Mass+AntiMass)/InitialMass));

        G4int loopCounter = 0;
  do
  {
    Pt=SampleQuarkPt(Pabs); Pt.setZ(0); G4double Pt2=Pt.mag2();
    MassMt    = std::sqrt(    Mass *     Mass + Pt2);
    AntiMassMt= std::sqrt(AntiMass * AntiMass + Pt2);
  }
  while ( (InitialMass < MassMt + AntiMassMt) && ++loopCounter < maxNumberOfLoops ); 

  if (Mass > 930. || AntiMass > 930.) SigmaQT=SigmaQTw;

        if ( loopCounter >= maxNumberOfLoops ) {
            AvailablePz2 = 0.0;
        }

  AvailablePz2= sqr(InitialMass*InitialMass - sqr(MassMt) - sqr(AntiMassMt)) -
        4.*sqr(MassMt*AntiMassMt);

  AvailablePz2 /=(4.*InitialMass*InitialMass);
  AvailablePz = std::sqrt(AvailablePz2);

  G4double Px=Pt.getX();
  G4double Py=Pt.getY();

  Mom->setPx(Px); Mom->setPy(Py); Mom->setPz(AvailablePz);
  Mom->setE(std::sqrt(sqr(MassMt)+AvailablePz2));

  AntiMom->setPx(-Px); AntiMom->setPy(-Py); AntiMom->setPz(-AvailablePz);
  AntiMom->setE (std::sqrt(sqr(AntiMassMt)+AvailablePz2));

        #ifdef debug_LUNDfragmentation
        G4cout<<"Fmass Mom "<<Mom->getX()<<" "<<Mom->getY()<<" "<<Mom->getZ()<<" "<<Mom->getT()<<G4endl;
        G4cout<<"Smass Mom "<<AntiMom->getX()<<" "<<AntiMom->getY()<<" "<<AntiMom->getZ()
              <<" "<<AntiMom->getT()<<G4endl;
        #endif
}

//------------------------------------------------------------------------

G4double G4LundStringFragmentation::lambda(G4double S, G4double m1_Sqr, G4double m2_Sqr)
{ 
  G4double lam = sqr(S - m1_Sqr - m2_Sqr) - 4.*m1_Sqr*m2_Sqr;
  return lam;
}

// --------------------------------------------------------------
G4LundStringFragmentation::~G4LundStringFragmentation()
{}