EvtHypNonLepton.cc

Go to the documentation of this file.

//-----------------------------------------------------------------------------------------------
//
// Module: EvtHypNonLepton.cpp
//
// Desription: Routine to implement Hyperon(s=1/2) -> Baryon(s=1/2) + Scalar decays accroding to
//             Review Of Particle Physics 2004, Phys.Lett.B, Vol.592, p.864
//
// Modification history:
//
//  09/02/2009  PR   Corrected Delta sign
//  20/02/2005  PR   Module created according to PHSP and Lb2Lll model
//
//-----------------------------------------------------------------------------------------------
 
#ifdef WIN32
#pragma warning( disable : 4786 )
// Disable anoying warning about symbol size
#endif
 
#include "EvtGenModels/EvtHypNonLepton.hh"
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtDiracSpinor.hh"
#include "EvtGenBase/EvtTensor4C.hh"
#include "EvtGenBase/EvtVector4C.hh"
#include "EvtGenBase/EvtVector4R.hh"
#include "EvtGenBase/EvtComplex.hh"
#include "EvtGenBase/EvtGammaMatrix.hh"
 
 
EvtHypNonLepton::~EvtHypNonLepton() {}
 
EvtDecayBase* EvtHypNonLepton::clone(){
  return new EvtHypNonLepton;
}
 
void EvtHypNonLepton::getName(std::string& model_name){
  model_name= "HypNonLepton";
}
 
void EvtHypNonLepton::init(){
 
  if(getNArg()<2 || getNArg()>3){ // alpha phi gamma delta
    report(ERROR,"EvtGen") << " ERROR: EvtHypNonLepton generator expected 2 or 3 arguments but found: " << getNArg() << std::endl;
    report(INFO ,"EvtGen") << "  1. Decay asymmetry parameter - alpha" << std::endl;
    report(INFO ,"EvtGen") << "  2. Parameter phi - in degrees (not radians)" << std::endl;
    report(INFO ,"EvtGen") << "  3. Note on every x-th decay" << std::endl;
    ::abort();
  }
 
  if(getNDaug()!=2){ // Check that there are 2 daughters only
    report(ERROR,"EvtGen") << " ERROR: EvtHypNonLepton generator expected 2 daughters but found: " << getNDaug() << std::endl;
    ::abort();
  }
 
  // Check particles spins
  if(EvtSpinType::getSpin2(EvtPDL::getSpinType(getParentId()))!=1){
    report(ERROR,"EvtGen") << " ERROR: EvtHypNonLepton generator expected dirac parent particle, but found " << EvtSpinType::getSpin2(EvtPDL::getSpinType(getParentId())) << " spin degrees of freedom" << std::endl;
    ::abort();
  }
  if(EvtSpinType::getSpin2(EvtPDL::getSpinType(getDaug(0)))!=1){
    report(ERROR,"EvtGen") << " ERROR: EvtHypNonLepton generator expected the first child to be dirac particle, but found " << EvtSpinType::getSpin2(EvtPDL::getSpinType(getDaug(0))) << " spin degrees of freedom" << std::endl;
    ::abort();
  }
  if(EvtSpinType::getSpin2(EvtPDL::getSpinType(getDaug(1)))!=0){
    report(ERROR,"EvtGen") << " ERROR: EvtHypNonLepton generator expected the second child to be scalar particle, but found " << EvtSpinType::getSpin2(EvtPDL::getSpinType(getDaug(1))) << " spin degrees of freedom" << std::endl;
    ::abort();
  }
 
  // Read all parameters
  m_alpha = getArg(0);
  m_phi   = getArg(1)*EvtConst::pi/180;
  if(getNArg()==3) m_noTries = static_cast<long>(getArg(2));
  else             m_noTries = 0;
 
  // calculate additional parameters
  double p,M,m1,m2;
  double p_to_s,beta,delta,gamma;
 
  M  = EvtPDL::getMass(getParentId());
  m1 = EvtPDL::getMass(getDaug(0));
  m2 = EvtPDL::getMass(getDaug(1));
 
  if(m1+m2>=M){
    report(ERROR,"EvtGen") << " ERROR: EvtHypNonLepton found impossible decay: " << M << " --> " << m1 << " + " << m2 << " GeV\n" << std::endl;
    ::abort();
  }
 
  p = sqrt(M*M-(m1+m2)*(m1+m2))*sqrt(M*M-(m1-m2)*(m1-m2))/2./M;
 
  beta = sqrt(1.-m_alpha*m_alpha)*sin(m_phi);
  delta = -atan2(beta,m_alpha);
  gamma = sqrt(1.-m_alpha*m_alpha-beta*beta);
  p_to_s = sqrt((1.-gamma)/(1.+gamma));
 
  m_B_to_A = p_to_s*(m1+sqrt(p*p+m1*m1))/p*EvtComplex(cos(delta),sin(delta));
 
}
 
void EvtHypNonLepton::initProbMax(){
 
  double maxProb,m1,m2,M,p;
 
  M=EvtPDL::getMass(getParentId());
  m1=EvtPDL::getMass(getDaug(0));
  m2=EvtPDL::getMass(getDaug(1));
 
  if(m1+m2>=M){
    report(ERROR,"EvtGen") << " ERROR: EvtHypNonLepton found impossible decay: " << M << " --> " << m1 << " + " << m2 << " GeV\n" << std::endl;
    ::abort();
  }
 
  p=sqrt(M*M-(m1+m2)*(m1+m2))*sqrt(M*M-(m1-m2)*(m1-m2))/2/M;
  maxProb=16*M*(sqrt(p*p+m1*m1)+m1+abs(m_B_to_A)*abs(m_B_to_A)*(sqrt(p*p+m1*m1)-m1));
  //maxProb *= G_F*M_pi*M_pi;
 
  setProbMax(maxProb);
  report(INFO,"EvtGen") << " EvtHypNonLepton set up maximum probability to " << maxProb << std::endl;
 
}
 
void EvtHypNonLepton::decay(EvtParticle* parent){
 
  parent->initializePhaseSpace(getNDaug(),getDaugs());
  calcAmp(&_amp2,parent);
  
}
 
void EvtHypNonLepton::calcAmp(EvtAmp *amp,EvtParticle *parent){
 
  static long noTries=0;
  int i;
  EvtComplex Matrix[2][2],B_to_A;
 
  //G_F  = 1.16637e-5;
  //M_pi = 0.13957;
 
  for(i=0;i<4;i++){
    //std::cout << "--------------------------------------------------" << std::endl;
    Matrix[i/2][i%2]  = EvtLeptonSCurrent(parent->sp(i/2),parent->getDaug(0)->spParent(i%2));
    //std::cout << "Matrix = " << Matrix[i/2][i%2] << std::endl;
    Matrix[i/2][i%2] -= m_B_to_A*EvtLeptonPCurrent(parent->sp(i/2),parent->getDaug(0)->spParent(i%2));
    //std::cout << "Matrix = " << Matrix[i/2][i%2] << std::endl;
    //Matrix[i/2][i%2] *= G_F*M_pi*M_pi;
    //std::cout << "Matrix = " << Matrix[i/2][i%2] << std::endl;
    //std::cout << "--------------------------------------------------" << std::endl;
    amp->vertex(i/2,i%2,Matrix[i/2][i%2]);
  }
 
  if(m_noTries>0) if(!((++noTries)%m_noTries)) report(DEBUG,"EvtGen") << " EvtHypNonLepton already finished " << noTries << " matrix element calculations" << std::endl;
}