EvtSingleParticle.cpp

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* Copyright 1998-2020 CERN for the benefit of the EvtGen authors       *
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* This file is part of EvtGen.                                         *
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#include "EvtGenModels/EvtSingleParticle.hh"
 
#include "EvtGenBase/EvtConst.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtRandom.hh"
#include "EvtGenBase/EvtReport.hh"
 
#include <stdlib.h>
#include <string>
using std::endl;
 
std::string EvtSingleParticle::getName() const
{
    return "SINGLE";
}
 
EvtDecayBase* EvtSingleParticle::clone() const
{
    return new EvtSingleParticle();
}
 
void EvtSingleParticle::initProbMax()
{
    noProbMax();
}
 
void EvtSingleParticle::init()
{
    //turn off checks for charge conservation
    disableCheckQ();
 
    if ( ( getNArg() == 6 ) || ( getNArg() == 4 ) || ( getNArg() == 2 ) ) {
        if ( getNArg() == 6 ) {
            //copy the arguments into eaiser to remember names!
 
            m_pmin = getArg( 0 );
            m_pmax = getArg( 1 );
 
            m_cthetamin = getArg( 2 );
            m_cthetamax = getArg( 3 );
 
            m_phimin = getArg( 4 );
            m_phimax = getArg( 5 );
        }
 
        if ( getNArg() == 4 ) {
            //copy the arguments into eaiser to remember names!
 
            m_pmin = getArg( 0 );
            m_pmax = getArg( 1 );
 
            m_cthetamin = getArg( 2 );
            m_cthetamax = getArg( 3 );
 
            m_phimin = 0.0;
            m_phimax = EvtConst::twoPi;
        }
 
        if ( getNArg() == 2 ) {
            //copy the arguments into eaiser to remember names!
 
            m_pmin = getArg( 0 );
            m_pmax = getArg( 1 );
 
            m_cthetamin = -1.0;
            m_cthetamax = 1.0;
 
            m_phimin = 0.0;
            m_phimax = EvtConst::twoPi;
        }
 
    } else {
        EvtGenReport( EVTGEN_ERROR, "EvtGen" )
            << "EvtSingleParticle generator expected "
            << " 6, 4, or 2 arguments but found:" << getNArg() << endl;
        EvtGenReport( EVTGEN_ERROR, "EvtGen" )
            << "Will terminate execution!" << endl;
        ::abort();
    }
 
    EvtGenReport( EVTGEN_INFO, "EvtGen" )
        << "The single particle generator has been configured:" << endl;
    EvtGenReport( EVTGEN_INFO, "EvtGen" )
        << m_pmax << " > p > " << m_pmin << endl;
    EvtGenReport( EVTGEN_INFO, "EvtGen" )
        << m_cthetamax << " > costheta > " << m_cthetamin << endl;
    EvtGenReport( EVTGEN_INFO, "EvtGen" )
        << m_phimax << " > phi > " << m_phimin << endl;
}
 
void EvtSingleParticle::decay( EvtParticle* p )
{
    EvtParticle* d;
    EvtVector4R p4;
 
    double mass = EvtPDL::getMass( getDaug( 0 ) );
 
    p->makeDaughters( getNDaug(), getDaugs() );
    d = p->getDaug( 0 );
 
    //generate flat distribution in p
    //we are now in the parents restframe! This means the
    //restframe of the e+e- collison.
    double pcm = EvtRandom::Flat( m_pmin, m_pmax );
    //generate flat distribution in phi.
    double phi = EvtRandom::Flat( m_phimin, m_phimax );
 
    double cthetalab;
 
    do {
        //generate flat distribution in costheta
        double ctheta = EvtRandom::Flat( m_cthetamin, m_cthetamax );
        double stheta = sqrt( 1.0 - ctheta * ctheta );
        p4.set( sqrt( mass * mass + pcm * pcm ), pcm * cos( phi ) * stheta,
                pcm * sin( phi ) * stheta, pcm * ctheta );
 
        d->init( getDaug( 0 ), p4 );
 
        //get 4 vector in the lab frame!
        EvtVector4R p4lab = d->getP4Lab();
        cthetalab = p4lab.get( 3 ) / p4lab.d3mag();
    } while ( cthetalab > m_cthetamax || cthetalab < m_cthetamin );
 
    return;
}