chigen::PythiaChiGen Class Reference

#include <PythiaChiGen.h>

Public Member Functions
	PythiaChiGen (PartonicModel &partonicModel, int maxTries=30, bool doHadronization=true)
PartonicModel &	getPartonicModel () const
virtual	~PythiaChiGen ()
Event *	next ()
	ClassDef (PythiaChiGen, 1)

Private Member Functions
void	calculateKinematics ()
void	calculateHadronRemnants (double x, double hadronPz, Vec4 &u, Vec4 &d)
void	decay (Event &event)
void	fillColorEvent (Event &event)

Private Attributes
double	eCM
PartonicModel &	partonicModel
int	maxTries
double	protonPz
bool	doHadronization
Vec4	uMomentum
Vec4	dMomentum
Vec4	ubarMomentum
Vec4	dbarMomentum
Vec4	mesonMomentum
Vec4	gluonMomentum
Vec4	boost
EvtStdHep	evtstdhep

Static Private Attributes
static int	COLORS [] = {101, 102, 103}

Detailed Description

Definition at line 19 of file PythiaChiGen.h.

Constructor & Destructor Documentation

chigen::PythiaChiGen::PythiaChiGen	(	PartonicModel &	partonicModel,
		int	maxTries = 30,
		bool	doHadronization = true
	)

Parameters

partonicModel	partonic model
maxTries	max errors number
doHadronization	perform hadronization

Definition at line 16 of file PythiaChiGen.cxx.

References doHadronization, chigen::PartonicModel::eCM, eCM, chigen::ensure_chigen_is_initialized(), maxTries, protonPz, and sqrt().

: partonicModel(partonicModelRef) {
    chigen::ensure_chigen_is_initialized();
    eCM = partonicModelRef.eCM;
    protonPz = sqrt(pow2(eCM) / 4 - 1);
    maxTries = tries;
    doHadronization = hadronize;
}

chigen::PythiaChiGen::~PythiaChiGen ( )

virtual

Definition at line 26 of file PythiaChiGen.cxx.

                                  {
}

Member Function Documentation

void chigen::PythiaChiGen::calculateHadronRemnants ( double  x, double  hadronPz, Vec4 &  u, Vec4 &  d  )

private

Calculates remnants kinematics

Parameters

x	x-fraction
hadronPz	hadron z-momentum
u	u (anti) quark
d	d (anti) quark

Definition at line 63 of file PythiaChiGen.cxx.

References cos(), chigen::ChiGenRandomEngine::flat(), phi, chigen::random::random_engine, sin(), and theta.

                                                                                            {

    Vec4 totalRemnant(0, 0, (1 - x) * hadronPz, eCM / 2 - x * abs(hadronPz));
    double halfRemnantInvMass = totalRemnant.mCalc() / 2;
    //make remnants pT
    double theta = chigen::random::random_engine->flat() * M_PI;
    double sine = halfRemnantInvMass * sin(theta), cosine = halfRemnantInvMass * cos(theta);
    u.p(0, sine, cosine, halfRemnantInvMass);
    d.p(0, -sine, -cosine, halfRemnantInvMass);

    //rotate vectors in XY plane
    double phi = chigen::random::random_engine->flat()* 2 * M_PI;
    u.rot(0, phi);
    d.rot(0, phi);

    //boost to lab frame
    u.bst(totalRemnant);
    d.bst(totalRemnant);
}

void chigen::PythiaChiGen::calculateKinematics ( )

private

Calculates hadron-level kinematics

Definition at line 31 of file PythiaChiGen.cxx.

References chigen::ChiGenRandomEngine::flat(), chigen::random::random_engine, and sqrt().

                                             {

    double pT = sqrt(partonicModel.uH * partonicModel.tH / partonicModel.sH);
    double pL = (partonicModel.tH - partonicModel.uH) / (2 * sqrt(partonicModel.sH));
    double mesonE = sqrt(partonicModel.mesonMass2 + pow2(pT) + pow2(pL));
    double gluonE = sqrt(pow2(pT) + pow2(pL));


    //quarkonia
    mesonMomentum = Vec4(0., pT, pL, mesonE);
    //gluon
    gluonMomentum = Vec4(0., -pT, -pL, gluonE);

    //rotate vectors in XY plane
    double hardPhiAngle = chigen::random::random_engine->flat()* 2 * M_PI;
    mesonMomentum.rot(0, hardPhiAngle);
    gluonMomentum.rot(0, hardPhiAngle);

    //boost from hard c.m. to hadronic c.m.    
    boost = Vec4(0., 0., (partonicModel.x1 - partonicModel.x2) * protonPz,
            (partonicModel.x1 + partonicModel.x2) * protonPz);
    //do not boost meson momentum until EvtGen perform decay!!!
    //mesonMomentum.bst(boost) <-- this will destroy polarization
    gluonMomentum.bst(boost);

    //remnants kinematics
    //proton remnants
    calculateHadronRemnants(partonicModel.x1, protonPz, uMomentum, dMomentum);
    //antiproton remnants
    calculateHadronRemnants(partonicModel.x2, -protonPz, ubarMomentum, dbarMomentum);
}

chigen::PythiaChiGen::ClassDef	(	PythiaChiGen	,
		1
	)

void chigen::PythiaChiGen::decay ( Event &  event )

private

Perform decay of polarized chi-meson.

Parameters

event

event reference

Definition at line 83 of file PythiaChiGen.cxx.

References chigen::evtgen::evt_gen, chigen::isCharmonia(), and p.

                                           {
    //lets decay polarized meson via EvtGen
    EvtVector4R chiMomentum(
            mesonMomentum.e(),
            mesonMomentum.px(),
            mesonMomentum.py(),
            mesonMomentum.pz());


    EvtParticle *chiMeson =
            EvtParticleFactory::particleFactory(partonicModel.evtId, chiMomentum);
    chiMeson->setSpinDensityForward(partonicModel.spinDensity);

    //decay
    chigen::evtgen::evt_gen->generateDecay(chiMeson);
    //write info
    evtstdhep.init();
    chiMeson->makeStdHep(evtstdhep);

    assert(evtstdhep.getNPart() == 5);
    int id;
    EvtVector4R vertexPoint, evtMomentum;
    for (int particleNumber = 0, size = evtstdhep.getNPart();
            particleNumber < size; ++particleNumber) {
        vertexPoint = evtstdhep.getX4(particleNumber);
        evtMomentum = evtstdhep.getP4(particleNumber);

        Pythia8::Particle p;
        p.id(id = evtstdhep.getStdHepID(particleNumber));
        p.px(evtMomentum.get(1));
        p.py(evtMomentum.get(2));
        p.pz(evtMomentum.get(3));
        p.e(evtMomentum.get(0));
        //boost from hard c.m. frame to hadronic c.m. frame
        p.bst(boost);

        p.daughter1(evtstdhep.getFirstDaughter(particleNumber) + 1);
        p.daughter2(evtstdhep.getLastDaughter(particleNumber) + 1);
        p.mother1(evtstdhep.getFirstMother(particleNumber) + 1);
        p.mother2(evtstdhep.getLastMother(particleNumber) + 1);
        if (chigen::isCharmonia(id))
            p.status(-33);
        else
            p.status(91);

        event.append(p);
    }
}

void chigen::PythiaChiGen::fillColorEvent ( Event &  event )

private

Fills the event by hadronic remnants & gluon

Parameters

event

event reference

Definition at line 132 of file PythiaChiGen.cxx.

                                                    {
    // first setup colors and anti-colors
    // the following color mask is adopted:
    //
    //               u (bar)      d (bar)        g     
    // color     :    101          102          103
    // anti-color:  COLORS[0]    COLORS[1]    COLORS[2]

    // randomly shuffle colors 
    std::random_shuffle(COLORS, COLORS + 3); //todo use same seed as in rndm

    //already added chi-meson in decay()
    //    //filling the event record:    
    //    //quarkonia
    //    event.append(partonicModel->pdgId/*id*/, 21 /*status code*/,
    //            0, 0/*colors*/,
    //            mesonMomentum /*4-momentum*/, partonicModel->mesonMass /*mass*/);

    //gluon
    event.append(21/*id*/, 23 /*status code (should be hadronized)*/,
            103, COLORS[2]/*colors*/,
            gluonMomentum /*4-momentum*/, 0.0 /*mass*/);


    //u-quark
    event.append(2/*id*/, 23 /*status code (should be hadronized)*/,
            101, 0/*colors*/,
            uMomentum/*4-momentum*/, 0.0/* mass*/);

    //d-quark
    event.append(1/*id*/, 23 /*status code (should be hadronized)*/,
            102, 0/*colors*/,
            dMomentum/*4-momentum*/, 0.0/* mass*/);

    //u-bar
    event.append(-2/*id*/, 23 /*status code (should be hadronized)*/,
            0, COLORS[0]/*colors*/,
            ubarMomentum/*4-momentum*/, 0.0/* mass*/);

    //d-bar
    event.append(-1/*id*/, 23 /*status code (should be hadronized)*/,
            0, COLORS[1]/*colors*/,
            dbarMomentum/*4-momentum*/, 0.0 /*mass*/);
}

PartonicModel& chigen::PythiaChiGen::getPartonicModel ( ) const

inline

Definition at line 30 of file PythiaChiGen.h.

                                                {
            return partonicModel;
        }

Event * chigen::PythiaChiGen::next

(

)

Calculates and returns the next event

Returns

event

Definition at line 177 of file PythiaChiGen.cxx.

References next, and chigen::pythia::pythia.

                                {
    Event& event = chigen::pythia::pythia->event;
    //reset event is necessary
    event.reset();

    //number of attempts
    int attempt = 0;
    while (!partonicModel.next() && attempt++ < maxTries);
    //parton level failed
    if (attempt >= maxTries)
        Fatal("PythiaHadronizationModel::next", "Can't set kinematics at parton level.");

    attempt = 0;
    calculateKinematics();
    decay(event);
    fillColorEvent(event);

    if (doHadronization) {
        while (!chigen::pythia::pythia->next() && attempt++ < maxTries) {
            event.reset();
            calculateKinematics();
            decay(event);
            fillColorEvent(event);
        }
        //hadron level failed
        if (attempt >= maxTries)
            Fatal("PythiaHadronizationModel::next", "Failed to hadronize remnants.");
    }
    return &event;
}

Member Data Documentation

Vec4 chigen::PythiaChiGen::boost

private

Boost from hard c.m. frame to hadronic c.m. frame

Definition at line 80 of file PythiaChiGen.h.

int chigen::PythiaChiGen::COLORS = {101, 102, 103}

staticprivate

Colors of particles:

u-quark : 101 d-quark : 102 gluon (color) : 103

Definition at line 92 of file PythiaChiGen.h.

Vec4 chigen::PythiaChiGen::dbarMomentum

private

Definition at line 72 of file PythiaChiGen.h.

Vec4 chigen::PythiaChiGen::dMomentum

private

Definition at line 68 of file PythiaChiGen.h.

bool chigen::PythiaChiGen::doHadronization

private

Do hadronization or not

Definition at line 64 of file PythiaChiGen.h.

Referenced by PythiaChiGen().

double chigen::PythiaChiGen::eCM

private

Hadronic c.m. energy

Definition at line 48 of file PythiaChiGen.h.

Referenced by PythiaChiGen().

EvtStdHep chigen::PythiaChiGen::evtstdhep

private

EvtGen data on chi_c decay

Definition at line 84 of file PythiaChiGen.h.

Vec4 chigen::PythiaChiGen::gluonMomentum

private

Definition at line 76 of file PythiaChiGen.h.

int chigen::PythiaChiGen::maxTries

private

Maximum number of tries to hadronize with diff kinematics

Definition at line 56 of file PythiaChiGen.h.

Referenced by PythiaChiGen().

Vec4 chigen::PythiaChiGen::mesonMomentum

private

Hard process particles

Definition at line 76 of file PythiaChiGen.h.

PartonicModel& chigen::PythiaChiGen::partonicModel

private

Underlying parton model

Definition at line 52 of file PythiaChiGen.h.

double chigen::PythiaChiGen::protonPz

private

Proton momentum

Definition at line 60 of file PythiaChiGen.h.

Referenced by PythiaChiGen().

Vec4 chigen::PythiaChiGen::ubarMomentum

private

Antiproton remnants

Definition at line 72 of file PythiaChiGen.h.

Vec4 chigen::PythiaChiGen::uMomentum

private

Proton remnants

Definition at line 68 of file PythiaChiGen.h.

---

The documentation for this class was generated from the following files:

• PythiaChiGen.h
• PythiaChiGen.cxx