EvtSingleParticle2.cc

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//--------------------------------------------------------------------------
//
// Environment:
//      This software is part of the EvtGen package developed jointly
//      for the BaBar and CLEO collaborations.  If you use all or part
//      of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/COPYRIGHT
//      Copyright (C) 1998      Caltech, UCSB
//
// Module: EvtSingleParticle.cc
//
// Description: Special model to generate single particles.
//
// Modification history:
//
//    RYD       Febuary 17,1998       Module created
//
//------------------------------------------------------------------------
//
#include "EvtSingleParticle2.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;
 
EvtSingleParticle2::~EvtSingleParticle2() {}
 
void EvtSingleParticle2::getName( std::string& model_name ) { model_name = "SINGLE2"; }
 
EvtDecayBase* EvtSingleParticle2::clone() { return new EvtSingleParticle2(); }
 
void EvtSingleParticle2::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!
 
      pxymin = getArg( 0 );
      pxymax = getArg( 1 );
 
      thetamin = getArg( 2 );
      thetamax = getArg( 3 );
 
      phimin = getArg( 4 );
      phimax = getArg( 5 );
    }
 
    if ( getNArg() == 4 )
    {
      // copy the arguments into eaiser to remember names!
      pxymin = getArg( 0 );
      pxymax = getArg( 1 );
 
      thetamin = getArg( 2 );
      thetamax = getArg( 3 );
 
      phimin = 0.0;
      phimax = EvtConst::twoPi;
    }
 
    if ( getNArg() == 2 )
    {
      // copy the arguments into eaiser to remember names!
      pxymin = getArg( 0 );
      pxymax = getArg( 1 );
 
      thetamin = 0.376383;
      thetamax = 2.76521; //|cos(theta)|<0.93
 
      phimin = 0.0;
      phimax = EvtConst::twoPi;
    }
  }
  else
  {
 
    report( ERROR, "EvtGen" ) << "EvtSingleParticle generator expected "
                              << " 5, 3, or 1 arguments but found:" << getNArg() << endl;
    report( ERROR, "EvtGen" ) << "Will terminate execution!" << endl;
    ::abort();
  }
 
  report( INFO, "EvtGen" ) << "The single particle generator has been configured:" << endl;
  report( INFO, "EvtGen" ) << thetamax << " > theta > " << thetamin << endl;
  report( INFO, "EvtGen" ) << phimax << " > phi > " << phimin << endl;
}
 
void EvtSingleParticle2::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 theta;
  if ( thetamax == thetamin ) { theta = thetamax; }
  else theta = EvtRandom::Flat( thetamin, thetamax );
  double phi;
  if ( phimin == phimax ) { phi = phimin; }
  else phi = EvtRandom::Flat( phimin, phimax );
  double pxy;
  if ( pxymin == pxymax ) { pxy = pxymin; }
  else pxy = EvtRandom::Flat( pxymin, pxymax );
 
  pmag      = pxy / sin( theta );
  cthetamax = cos( thetamax );
  cthetamin = cos( thetamin );
  double cthetalab;
 
  //  do{
  // generate flat distribution in costheta
 
  p4.set( sqrt( mass * mass + pmag * pmag ), pmag * cos( phi ) * sin( theta ),
          pmag * sin( phi ) * sin( theta ), pmag * cos( theta ) );
  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;
}