BesEvtGen-00-04-08/src/EvtGen/EvtGenBase/EvtResonance.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: EvtResonance.cc
//
// Description: resonance-defining class 
//
// Modification history:
//
//    NK        September 4, 1997      Module created
//
//------------------------------------------------------------------------
// 
#include "EvtGenBase/EvtPatches.hh"
#include <math.h>
#include "EvtGenBase/EvtVector4R.hh"
#include "EvtGenBase/EvtKine.hh"
#include "EvtGenBase/EvtComplex.hh"
#include "EvtGenBase/EvtResonance.hh"
#include "EvtGenBase/EvtReport.hh"
#include "EvtGenBase/EvtConst.hh"
using std::endl;
 
EvtResonance::~EvtResonance(){}
 
//operator
 
EvtResonance& EvtResonance::operator = ( const EvtResonance  &n)
{
  if ( &n == this ) return *this;
  _p4_p = n._p4_p;
  _p4_d1 = n._p4_d1;
  _p4_d2 = n._p4_d2;
  _ampl = n._ampl;
  _theta = n._theta;
  _gamma = n._gamma;
  _spin = n._spin;
  _bwm = n._bwm;
   return  *this;
}
 
//constructor
 
EvtResonance::EvtResonance(const EvtVector4R& p4_p, const EvtVector4R& p4_d1,
               const  EvtVector4R& p4_d2, double ampl, 
               double theta, double gamma, double bwm, int spin): 
  _p4_p(p4_p),_p4_d1(p4_d1), _p4_d2(p4_d2),_ampl(ampl), _theta(theta), 
  _gamma(gamma), _bwm(bwm), _spin(spin) {}
 
//amplitude function
 
EvtComplex EvtResonance::resAmpl() {
 
  double pi180inv = 1.0/EvtConst::radToDegrees;
 
  EvtComplex ampl;
  //EvtVector4R  _p4_d3 = _p4_p-_p4_d1-_p4_d2;
 
  //get cos of the angle between the daughters from their 4-momenta
  //and the 4-momentum of the parent
 
  //in general, EvtDecayAngle(parent, part1+part2, part1) gives the angle
  //the missing particle (not listed in the arguments) makes
  //with part2 in the rest frame of both
  //listed particles (12)
 
  //angle 3 makes with 2 in rest frame of 12 (CS3)  
  double cos_phi_0 = EvtDecayAngle(_p4_p, _p4_d1+_p4_d2, _p4_d1);
  //angle 3 makes with 1 in 12 is, of course, -cos_phi_0
 
  switch (_spin) {
 
  case 0 : 
    ampl=(_ampl*EvtComplex(cos(_theta*pi180inv),sin(_theta*pi180inv))*
      sqrt(_gamma/EvtConst::twoPi)*
      (1.0/((_p4_d1+_p4_d2).mass()-_bwm-EvtComplex(0.0,0.5*_gamma)))); 
    break;
 
  case 1 : 
    ampl=(_ampl*EvtComplex(cos(_theta*pi180inv),sin(_theta*pi180inv))*
      sqrt(_gamma/EvtConst::twoPi)*
      (cos_phi_0/((_p4_d1+_p4_d2).mass()-_bwm-EvtComplex(0.0,0.5*_gamma))));
    break;
 
  case 2: 
    ampl=(_ampl*EvtComplex(cos(_theta*pi180inv),sin(_theta*pi180inv))*
      sqrt(_gamma/EvtConst::twoPi)*
      ((1.5*cos_phi_0*cos_phi_0-0.5)/((_p4_d1+_p4_d2).mass()-_bwm-EvtComplex(0.0, 0.5*_gamma))));
    break;
             
  case 3:  
    ampl=(_ampl*EvtComplex(cos(_theta*pi180inv),sin(_theta*pi180inv))*
      sqrt(_gamma/EvtConst::twoPi)*
      ((2.5*cos_phi_0*cos_phi_0*cos_phi_0-1.5*cos_phi_0)/((_p4_d1+_p4_d2).mass()-_bwm-EvtComplex(0.0, 0.5*_gamma))));
    break;
 
  default:
    report(DEBUG,"EvtGen") << "EvtGen: wrong spin in EvtResonance" << endl;
    ampl = EvtComplex(0.0);
    break;         
 
  }
 
  return ampl;
}
 
EvtComplex EvtResonance::relBrWig(int i) {
 
//this function returns relativistic Breit-Wigner amplitude
//for a given resonance (for P-wave decays of scalars only at the moment!)
 
  EvtComplex BW;
  EvtVector4R  _p4_d3 = _p4_p-_p4_d1-_p4_d2;
  EvtVector4R _p4_12 = _p4_d1 + _p4_d2;
 
  //EvtVector4R _p4_pm3 = _p4_p - _p4_d3;
  //EvtVector4R _p4_1m2 = _p4_d1 - _p4_d2;
 
  //double msq12 = _p4_12.mass2();
  double msq13 = (_p4_d1 + _p4_d3).mass2();
  double msq23 = (_p4_d2 + _p4_d3).mass2();
  double msqParent = _p4_p.mass2();
  double msq1 = _p4_d1.mass2();
  double msq2 = _p4_d2.mass2();
  double msq3 = _p4_d3.mass2();  
 
  double M;
 
  double p2 = sqrt((_p4_12.mass2() - (_p4_d1.mass() + _p4_d2.mass())*(_p4_d1.mass() + _p4_d2.mass()))*(_p4_12.mass2() - (_p4_d1.mass() - _p4_d2.mass())*(_p4_d1.mass() - _p4_d2.mass())))/(2.0*_p4_12.mass());
 
  double p2R = sqrt((_bwm*_bwm - (_p4_d1.mass() + _p4_d2.mass())*(_p4_d1.mass() + _p4_d2.mass()))*(_bwm*_bwm - (_p4_d1.mass() - _p4_d2.mass())*(_p4_d1.mass() - _p4_d2.mass())))/(2.0*_bwm);
 
  double gam, R;
 
if (i == 1) {
//consider this the K resonance
 
  R = 2.0/(0.197);
 
}
else R = 5.0/(0.197);
  
  gam = _gamma*(_bwm/_p4_12.mass())*(p2/p2R)*(p2/p2R)*(p2/p2R)*((1 + R*R*p2R*p2R)/(1 + R*R*p2*p2));
  M = (msq13 - msq23 - (msqParent - msq3)*(msq1 - msq2)/(_bwm*_bwm))*sqrt((1 + R*R*p2R*p2R)/(1 + R*R*p2*p2)); 
  //M = (msq13 - msq23 - (msqParent - msq3)*(msq1 - msq2)/(_p4_12.mass2()))*sqrt((1 + R*R*p2R*p2R)/(1 + R*R*p2*p2)); 
 
  BW = sqrt(_gamma)*M/((_bwm*_bwm - _p4_12.mass2()) - EvtComplex(0.0,1.0)*gam*_bwm);
 
  return BW;
 
}