G4QGSMSplitableHadron.cc

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#include "G4QGSMSplitableHadron.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4ParticleTable.hh" 
#include "G4PionPlus.hh"
#include "G4PionMinus.hh"
#include "G4Gamma.hh"
#include "G4PionZero.hh"
#include "G4KaonPlus.hh"
#include "G4KaonMinus.hh"

// based on prototype by Maxim Komogorov
// Splitting into methods, and centralizing of model parameters HPW Feb 1999
// restructuring HPW Feb 1999
// fixing bug in the sampling of 'x', HPW Feb 1999
// fixing bug in sampling pz, HPW Feb 1999. 
// Code now also good for p-nucleus scattering (before only p-p), HPW Feb 1999.
// Using Parton more directly, HPW Feb 1999.
// Shortening the algorithm for sampling x, HPW Feb 1999.
// sampling of x replaced by formula, taking X_min into account in the correlated sampling. HPW, Feb 1999.
// logic much clearer now. HPW Feb 1999
// Removed the ordering problem. No Direction needed in selection of valence quark types. HPW Mar'99.
// Fixing p-t distributions for scattering of nuclei.
// Separating out parameters.

void G4QGSMSplitableHadron::InitParameters()
{
    // changing rapidity distribution for all
    alpha = -0.5; // Note that this number is still assumed in the algorithm
    // needs to be generalized.
    // changing rapidity distribution for projectile like
    beta = 2.5;// Note that this number is still assumed in the algorithm
    // needs to be generalized.
    theMinPz = 0.5*G4PionMinus::PionMinus()->GetPDGMass();
    //  theMinPz = 0.1*G4PionMinus::PionMinus()->GetPDGMass();
    //  theMinPz = G4PionMinus::PionMinus()->GetPDGMass();
    // as low as possible, otherwise, we have unphysical boundary conditions in the sampling.
    StrangeSuppress = 0.48;
    sigmaPt = 0.*GeV; // widens eta slightly, if increased to 1.7,
    // but Maxim's algorithm breaks energy conservation
    // to be revised.
    widthOfPtSquare = 0.01*GeV*GeV;
    Direction = FALSE;
    minTransverseMass = 1*keV;
} 

G4QGSMSplitableHadron::G4QGSMSplitableHadron() 
{
    InitParameters();
}

G4QGSMSplitableHadron::G4QGSMSplitableHadron(const G4ReactionProduct & aPrimary, G4bool aDirection)
:G4VSplitableHadron(aPrimary)
{
    InitParameters();
    Direction = aDirection;
}


G4QGSMSplitableHadron::G4QGSMSplitableHadron(const G4ReactionProduct & aPrimary)
:  G4VSplitableHadron(aPrimary)
{
    InitParameters();
}

G4QGSMSplitableHadron::G4QGSMSplitableHadron(const G4Nucleon & aNucleon)
:  G4VSplitableHadron(aNucleon)
{
    InitParameters();
}

G4QGSMSplitableHadron::G4QGSMSplitableHadron(const G4Nucleon & aNucleon, G4bool aDirection)
:  G4VSplitableHadron(aNucleon)
{
    InitParameters();
    Direction = aDirection;
}

G4QGSMSplitableHadron::~G4QGSMSplitableHadron(){}



//**************************************************************************************************************************

void G4QGSMSplitableHadron::SplitUp()
{  
    if (IsSplit()) return;
    Splitting();
    if (Color.size()!=0) return;
    if (GetSoftCollisionCount() == 0)
    {
        DiffractiveSplitUp();
    }
    else
    {
        SoftSplitUp();
    }
}

void G4QGSMSplitableHadron::DiffractiveSplitUp()
{   
    // take the particle definitions and get the partons HPW
    G4Parton * Left = NULL;
    G4Parton * Right = NULL;
    GetValenceQuarkFlavors(GetDefinition(), Left, Right);
    Left->SetPosition(GetPosition());
    Right->SetPosition(GetPosition());

    G4LorentzVector HadronMom = Get4Momentum();
    //std::cout << "DSU 1 - "<<HadronMom<<std::endl;

    // momenta of string ends
    G4double pt2 = HadronMom.perp2();
    G4double transverseMass2 = HadronMom.plus()*HadronMom.minus();
    G4double maxAvailMomentum2 = sqr(std::sqrt(transverseMass2) - std::sqrt(pt2));
    G4ThreeVector pt(minTransverseMass, minTransverseMass, 0);
    if(maxAvailMomentum2/widthOfPtSquare>0.01) pt = GaussianPt(widthOfPtSquare, maxAvailMomentum2);
    //std::cout << "DSU 1.1 - "<< maxAvailMomentum2<< pt <<std::endl;

    G4LorentzVector LeftMom(pt, 0.);
    G4LorentzVector RightMom;
    RightMom.setPx(HadronMom.px() - pt.x());
    RightMom.setPy(HadronMom.py() - pt.y());
    //std::cout << "DSU 2 - "<<RightMom<<" "<< LeftMom <<std::endl;

    G4double Local1 = HadronMom.minus() + (RightMom.perp2() - LeftMom.perp2())/HadronMom.plus();
    G4double Local2 = std::sqrt(std::max(0., sqr(Local1) - 4.*RightMom.perp2()*HadronMom.minus()/HadronMom.plus()));
    //std::cout << "DSU 3 - "<< Local1 <<" "<< Local2 <<std::endl;
    if (Direction) Local2 = -Local2;
    G4double RightMinus   = 0.5*(Local1 + Local2);
    G4double LeftMinus = HadronMom.minus() - RightMinus;
    //std::cout << "DSU 4 - "<< RightMinus <<" "<< LeftMinus << " "<<HadronMom.minus() <<std::endl;

    G4double LeftPlus  = LeftMom.perp2()/LeftMinus;
    G4double RightPlus = HadronMom.plus() - LeftPlus;
    //std::cout << "DSU 5 - "<< RightPlus <<" "<< LeftPlus <<std::endl;
    LeftMom.setPz(0.5*(LeftPlus - LeftMinus));
    LeftMom.setE (0.5*(LeftPlus + LeftMinus));
    RightMom.setPz(0.5*(RightPlus - RightMinus));
    RightMom.setE (0.5*(RightPlus + RightMinus));
    //std::cout << "DSU 6 - "<< LeftMom <<" "<< RightMom <<std::endl;
    Left->Set4Momentum(LeftMom);
    Right->Set4Momentum(RightMom);
    Color.push_back(Left);
    AntiColor.push_back(Right);
}


void G4QGSMSplitableHadron::SoftSplitUp()
{
    //... sample transversal momenta for sea and valence quarks
    G4double phi, pts;
    G4double SumPy = 0.;
    G4double SumPx = 0.;
    G4ThreeVector Pos    = GetPosition();
    G4int nSeaPair = GetSoftCollisionCount()-1;

    // here the condition,to ensure viability of splitting, also in cases
    // where difractive excitation occured together with soft scattering.
    //   G4double LightConeMomentum = (Direction)? Get4Momentum().plus() : Get4Momentum().minus();
    //   G4double Xmin = theMinPz/LightConeMomentum;
    G4double Xmin = theMinPz/( Get4Momentum().e() - GetDefinition()->GetPDGMass() );
    while(Xmin>=1-(2*nSeaPair+1)*Xmin) Xmin*=0.95;

    G4int aSeaPair;
    for (aSeaPair = 0; aSeaPair < nSeaPair; aSeaPair++)
    {
        //  choose quark flavour, d:u:s = 1:1:(1/StrangeSuppress-2)

        G4int aPDGCode = 1 + (G4int)(G4UniformRand()/StrangeSuppress);

        //  BuildSeaQuark() determines quark spin, isospin and colour
        //  via parton-constructor G4Parton(aPDGCode)

        G4Parton * aParton = BuildSeaQuark(false, aPDGCode, nSeaPair);

        //      G4cerr << "G4QGSMSplitableHadron::SoftSplitUp()" << G4endl;

        //      G4cerr << "Parton 1: "
        //             << " PDGcode: "  << aPDGCode
        //             << " - Name: "   << aParton->GetDefinition()->GetParticleName()
        //             << " - Type: "   << aParton->GetDefinition()->GetParticleType()
        //             << " - Spin-3: " << aParton->GetSpinZ()
        //             << " - Colour: " << aParton->GetColour() << G4endl;

        // save colour a spin-3 for anti-quark

        G4int firstPartonColour = aParton->GetColour();
        G4double firstPartonSpinZ = aParton->GetSpinZ();

        SumPx += aParton->Get4Momentum().px();
        SumPy += aParton->Get4Momentum().py();
        Color.push_back(aParton);

        // create anti-quark

        aParton = BuildSeaQuark(true, aPDGCode, nSeaPair);
        aParton->SetSpinZ(-firstPartonSpinZ);
        aParton->SetColour(-firstPartonColour);

        //      G4cerr << "Parton 2: "
        //             << " PDGcode: "  << -aPDGCode
        //             << " - Name: "   << aParton->GetDefinition()->GetParticleName()
        //             << " - Type: "   << aParton->GetDefinition()->GetParticleType()
        //             << " - Spin-3: " << aParton->GetSpinZ()
        //             << " - Colour: " << aParton->GetColour() << G4endl;
        //      G4cerr << "------------" << G4endl;

        SumPx += aParton->Get4Momentum().px();
        SumPy += aParton->Get4Momentum().py();
        AntiColor.push_back(aParton);
    }
    // Valence quark
    G4Parton* pColorParton = NULL;
    G4Parton* pAntiColorParton = NULL;
    GetValenceQuarkFlavors(GetDefinition(), pColorParton, pAntiColorParton);
    G4int ColorEncoding = pColorParton->GetPDGcode();

    pts   =  sigmaPt*std::sqrt(-std::log(G4UniformRand()));
    phi   = 2.*pi*G4UniformRand();
    G4double Px = pts*std::cos(phi);
    G4double Py = pts*std::sin(phi);
    SumPx += Px;
    SumPy += Py;

    if (ColorEncoding < 0) // use particle definition
    {
        G4LorentzVector ColorMom(-SumPx, -SumPy, 0, 0);
        pColorParton->Set4Momentum(ColorMom);
        G4LorentzVector AntiColorMom(Px, Py, 0, 0);
        pAntiColorParton->Set4Momentum(AntiColorMom);
    }
    else
    {
        G4LorentzVector ColorMom(Px, Py, 0, 0);
        pColorParton->Set4Momentum(ColorMom);
        G4LorentzVector AntiColorMom(-SumPx, -SumPy, 0, 0);
        pAntiColorParton->Set4Momentum(AntiColorMom);
    }
    Color.push_back(pColorParton);
    AntiColor.push_back(pAntiColorParton);

    // Sample X
    G4int nAttempt = 0;
    G4double SumX = 0;
    G4double aBeta = beta;
    G4double ColorX, AntiColorX;
    if (GetDefinition() == G4PionMinus::PionMinusDefinition()) aBeta = 1.;
    if (GetDefinition() == G4Gamma::GammaDefinition()) aBeta = 1.;
    if (GetDefinition() == G4PionPlus::PionPlusDefinition()) aBeta = 1.;
    if (GetDefinition() == G4PionZero::PionZeroDefinition()) aBeta = 1.;
    if (GetDefinition() == G4KaonPlus::KaonPlusDefinition()) aBeta = 0.;
    if (GetDefinition() == G4KaonMinus::KaonMinusDefinition()) aBeta = 0.;
    do
    {
        SumX = 0;
        nAttempt++;
        G4int    NumberOfUnsampledSeaQuarks = 2*nSeaPair;
        ColorX = SampleX(Xmin, NumberOfUnsampledSeaQuarks, 2*nSeaPair, aBeta);
        Color.back()->SetX(SumX = ColorX);// this is the valenz quark.
        for(G4int aPair = 0; aPair < nSeaPair; aPair++)
        {
            NumberOfUnsampledSeaQuarks--;
            ColorX = SampleX(Xmin, NumberOfUnsampledSeaQuarks, 2*nSeaPair, aBeta);
            Color[aPair]->SetX(ColorX);
            SumX += ColorX;
            NumberOfUnsampledSeaQuarks--;
            AntiColorX = SampleX(Xmin, NumberOfUnsampledSeaQuarks, 2*nSeaPair, aBeta);
            AntiColor[aPair]->SetX(AntiColorX); // the 'sea' partons
            SumX += AntiColorX;
            if (1. - SumX <= Xmin)  break;
        }
    }
    while (1. - SumX <= Xmin);

    (*(AntiColor.end()-1))->SetX(1. - SumX); // the di-quark takes the rest, then go to momentum
    G4double lightCone  = ((!Direction) ? Get4Momentum().minus() : Get4Momentum().plus());
    G4double lightCone2 = ((!Direction) ? Get4Momentum().plus() : Get4Momentum().minus());
    for(aSeaPair = 0; aSeaPair < nSeaPair+1; aSeaPair++)
    {
        G4Parton* aParton = Color[aSeaPair];
        aParton->DefineMomentumInZ(lightCone, lightCone2, Direction);

        aParton = AntiColor[aSeaPair];
        aParton->DefineMomentumInZ(lightCone, lightCone2, Direction);
    }
    return;
} 

void G4QGSMSplitableHadron::GetValenceQuarkFlavors(const G4ParticleDefinition * aPart, G4Parton *& Parton1, G4Parton *& Parton2)
{
    // Note! convention aEnd = q or (qq)bar and bEnd = qbar or qq.
    G4int aEnd;
    G4int bEnd;
    G4int HadronEncoding = aPart->GetPDGEncoding();
    if (aPart->GetBaryonNumber() == 0)
    {
        theMesonSplitter.SplitMeson(HadronEncoding, &aEnd, &bEnd);
    }
    else
    {
        theBaryonSplitter.SplitBarion(HadronEncoding, &aEnd, &bEnd);
    }

    Parton1 = new G4Parton(aEnd);
    Parton1->SetPosition(GetPosition());

    //  G4cerr << "G4QGSMSplitableHadron::GetValenceQuarkFlavors()" << G4endl;
    //  G4cerr << "Parton 1: "
    //         << " PDGcode: "  << aEnd
    //         << " - Name: "   << Parton1->GetDefinition()->GetParticleName()
    //         << " - Type: "   << Parton1->GetDefinition()->GetParticleType()
    //         << " - Spin-3: " << Parton1->GetSpinZ()
    //         << " - Colour: " << Parton1->GetColour() << G4endl;

    Parton2 = new G4Parton(bEnd);
    Parton2->SetPosition(GetPosition());

    //  G4cerr << "Parton 2: "
    //         << " PDGcode: "  << bEnd
    //         << " - Name: "   << Parton2->GetDefinition()->GetParticleName()
    //         << " - Type: "   << Parton2->GetDefinition()->GetParticleType()
    //         << " - Spin-3: " << Parton2->GetSpinZ()
    //         << " - Colour: " << Parton2->GetColour() << G4endl;
    //  G4cerr << "... now checking for color and spin conservation - yielding: " << G4endl;

    // colour of parton 1 choosen at random by G4Parton(aEnd)
    // colour of parton 2 is the opposite:

    Parton2->SetColour(-(Parton1->GetColour()));

    // isospin-3 of both partons is handled by G4Parton(PDGCode)

    // spin-3 of parton 1 and 2 choosen at random by G4Parton(aEnd)
    // spin-3 of parton 2 may be constrained by spin of original particle:

    if ( std::abs(Parton1->GetSpinZ() + Parton2->GetSpinZ()) > aPart->GetPDGSpin())
    {
        Parton2->SetSpinZ(-(Parton2->GetSpinZ()));    
    }

    //  G4cerr << "Parton 2: "
    //         << " PDGcode: "  << bEnd
    //         << " - Name: "   << Parton2->GetDefinition()->GetParticleName()
    //         << " - Type: "   << Parton2->GetDefinition()->GetParticleType()
    //         << " - Spin-3: " << Parton2->GetSpinZ()
    //         << " - Colour: " << Parton2->GetColour() << G4endl;
    //  G4cerr << "------------" << G4endl;

}


G4ThreeVector G4QGSMSplitableHadron::GaussianPt(G4double widthSquare, G4double maxPtSquare)
{
    G4double R;
    while((R = -widthSquare*std::log(G4UniformRand())) > maxPtSquare) {;}
    R = std::sqrt(R);
    G4double phi = twopi*G4UniformRand();
    return G4ThreeVector (R*std::cos(phi), R*std::sin(phi), 0.);
}

G4Parton * G4QGSMSplitableHadron::
BuildSeaQuark(G4bool isAntiQuark, G4int aPDGCode, G4int /* nSeaPair*/)
{
    if (isAntiQuark) aPDGCode*=-1;
    G4Parton* result = new G4Parton(aPDGCode);
    result->SetPosition(GetPosition());
    G4ThreeVector aPtVector = GaussianPt(sigmaPt, DBL_MAX);
    G4LorentzVector a4Momentum(aPtVector, 0);
    result->Set4Momentum(a4Momentum);
    return result;
}

G4double G4QGSMSplitableHadron::
SampleX(G4double anXmin, G4int nSea, G4int totalSea, G4double aBeta)
{
    G4double result;
    G4double x1, x2;
    G4double ymax = 0;
    for(G4int ii=1; ii<100; ii++)
    {
        G4double y = std::pow(1./G4double(ii), alpha);
        y *= std::pow( std::pow(1-anXmin-totalSea*anXmin, alpha+1) - std::pow(anXmin, alpha+1), nSea);
        y *= std::pow(1-anXmin-totalSea*anXmin, aBeta+1) - std::pow(anXmin, aBeta+1);
        if(y>ymax) ymax = y;
    }
    G4double y;
    G4double xMax=1-(totalSea+1)*anXmin;
    if(anXmin > xMax)
    {
        G4cout << "anXmin = "<<anXmin<<" nSea = "<<nSea<<" totalSea = "<< totalSea<<G4endl;
        throw G4HadronicException(__FILE__, __LINE__, "G4QGSMSplitableHadron - Fatal: Cannot sample parton densities under these constraints.");
    }
    do
    {
        x1 = G4RandFlat::shoot(anXmin, xMax);
        y = std::pow(x1, alpha);
        y *= std::pow( std::pow(1-x1-totalSea*anXmin, alpha+1) - std::pow(anXmin, alpha+1), nSea);
        y *= std::pow(1-x1-totalSea*anXmin, aBeta+1) - std::pow(anXmin, aBeta+1);
        x2 = ymax*G4UniformRand();
    }
    while(x2>y);
    result = x1;
    return result;
}