EvtJ2BB3.cc

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//--------------------------------------------------------------------------
//
// Environment:
//      This software is part of models developed at BES collaboration
//      based on the EvtGen framework.  If you use all or part
//      of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/BesCopyright
//      Copyright (A) 2006      Ping Rong-Gang, Pang Cai-Ying@IHEP
//
// Module: EvtJ2BB3.cc
//
// Description: Routine to decay J/psi-> B_8 bar B_10 with using the
//              GVDM approach.(see J.-G. Korner Z.Physik C-Particles
//              and Fields 33,529-535(1987))
//
// Modification history:
//
//    Pang C.-Y., Ping R.-G.    Mar, 2007       Module created
//
//------------------------------------------------------------------------
 
#include "EvtJ2BB3.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtHelSys.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtRaritaSchwinger.hh"
#include "../EvtGenBase/EvtRaritaSchwingerParticle.hh"
#include "../EvtGenBase/EvtReport.hh"
#include "../EvtGenBase/EvtTensor4C.hh"
#include "../EvtGenBase/EvtVector4C.hh"
#include "../EvtGenBase/EvtVector4R.hh"
#include "../EvtGenBase/EvtdFunctionSingle.hh"
#include <stdlib.h>
 
#include <string>
 
using std::cout;
using std::endl;
EvtJ2BB3::~EvtJ2BB3() {}
 
void EvtJ2BB3::getName( std::string& model_name ) { model_name = "J2BB3"; }
 
EvtDecayBase* EvtJ2BB3::clone() { return new EvtJ2BB3; }
 
void EvtJ2BB3::init() {
  // checkNArg(1);
  checkNDaug( 2 );
  checkSpinParent( EvtSpinType::VECTOR );
  checkSpinDaughter( 0, EvtSpinType::DIRAC );
  checkSpinDaughter( 1, EvtSpinType::RARITASCHWINGER );
}
 
/*
void EvtJ2BB3::initProbMax() {
 
  //Hard coded... should not be hard to calculate...
 //setProbMax(10000.0);  //the ProbMax value must have noticed.
   setProbMax(100.0);
}
*/
 
void EvtJ2BB3::decay( EvtParticle* p ) {
loop:
  p->initializePhaseSpace( getNDaug(), getDaugs() );
 
  EvtParticle *v, *s1;
  EvtVector4R  pv, ps, ppr;
 
  v   = p->getDaug( 0 );
  s1  = p->getDaug( 1 );
  pv  = v->getP4();
  ps  = s1->getP4();
  ppr = p->getP4();
  //  Put phase space results into the daughters.
  EvtHelSys angles( ppr, pv ); // using helicity sys. angles
  double    theta = angles.getHelAng( 1 );
  double    phi   = angles.getHelAng( 2 );
  double    gamma = 0;
 
  double m_b0 =
      EvtPDL::getMass( getDaug( 0 ) ); // the mass of daughter1 is large than daughter0.
  double m_b1 = EvtPDL::getMass( getDaug( 1 ) );
 
  double m_M  = EvtPDL::getMass( getParentId() );
  double M2   = pow( m_M, 2.0 );
  double b2_p = pow( ( m_b0 + m_b1 ), 2.0 );
  double b2_m = pow( ( m_b1 - m_b0 ), 2.0 );
 
  if ( M2 - b2_p <= 0 ) goto loop;
 
  double P_c = sqrt( ( M2 - b2_p ) * ( M2 - b2_m ) / ( 4.0 * M2 ) );
  double Q   = M2 - b2_p;
  double F1  = -0.54 / ( m_b0 * b2_p );
  double F2  = -0.54 * ( m_b1 - m_b0 ) / ( m_b0 * ( m_b0 + m_b1 ) );
  double F3  = -0.89 / m_b0;
  double H1, H0, Hm1;
 
  // OK. We have all  tested these parameters.
 
  if ( getNArg() > 0 )
  {
    alpha = getArg( 0 );
    H0    = 1.0;
    H1    = sqrt( ( 1 + alpha ) / ( 1 - alpha ) );
    Hm1   = H1;
  }
  else
  {
    H1 = -1.15 * P_c * m_M * ( -M2 * Q * F1 - Q * F2 + ( M2 - m_b0 * ( m_b0 + m_b1 ) ) * F3 ) /
         ( sqrt( Q ) * m_b1 );
    H0 =
        -0.82 * P_c * M2 *
        ( -( m_b1 - m_b0 ) * Q * F1 / m_b1 - Q * F2 / ( m_b1 * ( m_b1 - m_b0 ) ) + 2.0 * F3 ) /
        sqrt( Q );
    Hm1   = 2 * P_c * m_M * ( m_b0 + m_b1 ) * F3 / sqrt( Q );
    alpha = ( H1 * H1 + Hm1 * Hm1 - 2 * H0 * H0 ) / ( H1 * H1 + Hm1 * Hm1 + 2 * H0 * H0 );
  }
  // cout<<"------alpha="<<alpha<<";H0="<<H0<<";H1="<<H1<<";Hm1="<<Hm1<<endl;
 
  // J/psi helicity =1 corresponding index=0
  vertex( 0, 0, 0, Djmn( 1, 1, 0, phi, theta, gamma ) * H0 );
  vertex( 0, 0, 1, Djmn( 1, 1, -1, phi, theta, gamma ) * Hm1 );
  vertex( 0, 0, 2, 0.0 );
  vertex( 0, 0, 3, Djmn( 1, 1, 1, phi, theta, gamma ) * H1 );
  vertex( 0, 1, 0, Djmn( 1, 1, -1, phi, theta, gamma ) * H1 );
  vertex( 0, 1, 1, 0.0 );
  vertex( 0, 1, 2, Djmn( 1, 1, 1, phi, theta, gamma ) * Hm1 );
  vertex( 0, 1, 3, Djmn( 1, 1, 0, phi, theta, gamma ) * H0 );
  // J/psi helicity =-1 corresponding index=1
  vertex( 1, 0, 0, Djmn( 1, -1, 0, phi, theta, gamma ) * H0 );
  vertex( 1, 0, 1, Djmn( 1, -1, -1, phi, theta, gamma ) * Hm1 );
  vertex( 1, 0, 2, 0.0 );
  vertex( 1, 0, 3, Djmn( 1, -1, 1, phi, theta, gamma ) * H1 );
  vertex( 1, 1, 0, Djmn( 1, -1, -1, phi, theta, gamma ) * H1 );
  vertex( 1, 1, 1, 0.0 );
  vertex( 1, 1, 2, Djmn( 1, -1, 1, phi, theta, gamma ) * Hm1 );
  vertex( 1, 1, 3, Djmn( 1, -1, 0, phi, theta, gamma ) * H0 );
 
  // J/psi helicity =0 corresponding index=2
  vertex( 2, 0, 0, Djmn( 1, 0, 0, phi, theta, gamma ) * H0 );
  vertex( 2, 0, 1, Djmn( 1, 0, -1, phi, theta, gamma ) * Hm1 );
  vertex( 2, 0, 2, 0.0 );
  vertex( 2, 0, 3, Djmn( 1, 0, 1, phi, theta, gamma ) * H1 );
  vertex( 2, 1, 0, Djmn( 1, 0, -1, phi, theta, gamma ) * H1 );
  vertex( 2, 1, 1, 0.0 );
  vertex( 2, 1, 2, Djmn( 1, 0, 1, phi, theta, gamma ) * Hm1 );
  vertex( 2, 1, 3, Djmn( 1, 0, 0, phi, theta, gamma ) * H0 );
 
  return;
}