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EvtSingleParticle.cpp
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EvtSingleParticle.cpp
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/***********************************************************************
* Copyright 1998-2020 CERN for the benefit of the EvtGen authors *
* *
* This file is part of EvtGen. *
* *
* EvtGen is free software: you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation, either version 3 of the License, or *
* (at your option) any later version. *
* *
* EvtGen is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU General Public License for more details. *
* *
* You should have received a copy of the GNU General Public License *
* along with EvtGen. If not, see <https://www.gnu.org/licenses/>. *
***********************************************************************/
#include "EvtGenModels/EvtSingleParticle.hh"
#include "EvtGenBase/EvtConst.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtPatches.hh"
#include "EvtGenBase/EvtRandom.hh"
#include "EvtGenBase/EvtReport.hh"
#include <stdlib.h>
#include <string>
using std::endl;
std::string EvtSingleParticle::getName()
{
return "SINGLE";
}
EvtDecayBase* EvtSingleParticle::clone()
{
return new EvtSingleParticle();
}
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!
pmin = getArg( 0 );
pmax = getArg( 1 );
cthetamin = getArg( 2 );
cthetamax = getArg( 3 );
phimin = getArg( 4 );
phimax = getArg( 5 );
}
if ( getNArg() == 4 ) {
//copy the arguments into eaiser to remember names!
pmin = getArg( 0 );
pmax = getArg( 1 );
cthetamin = getArg( 2 );
cthetamax = getArg( 3 );
phimin = 0.0;
phimax = EvtConst::twoPi;
}
if ( getNArg() == 2 ) {
//copy the arguments into eaiser to remember names!
pmin = getArg( 0 );
pmax = getArg( 1 );
cthetamin = -1.0;
cthetamax = 1.0;
phimin = 0.0;
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" ) << pmax << " > p > " << pmin << endl;
EvtGenReport( EVTGEN_INFO, "EvtGen" )
<< cthetamax << " > costheta > " << cthetamin << endl;
EvtGenReport( EVTGEN_INFO, "EvtGen" )
<< phimax << " > phi > " << 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( pmin, pmax );
//generate flat distribution in phi.
double phi = EvtRandom::Flat( phimin, phimax );
double cthetalab;
do {
//generate flat distribution in costheta
double ctheta = EvtRandom::Flat( cthetamin, 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 > cthetamax || cthetalab < cthetamin );
return;
}

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