EvtEvalHelAmp.hh

//--------------------------------------------------------------------------
//
// 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) 2002      Caltech
//
// Module: EvtGen/EvtEvalHelAmp.hh
//
// Description: Class for evaluation of amplitudes in the 
//              helicity formalism.
//             
//
// Modification history:
//
//    RYD      October 24, 2002         Module created
//
//------------------------------------------------------------------------

#ifndef EVTEVALHELAMP_HH
#define EVTEVALHELAMP_HH

#include "EvtGenBase/EvtDecayAmp.hh"
#include "EvtGenBase/EvtSpinType.hh"
#include "EvtGenBase/EvtId.hh"

class EvtParticle;
class EvtAmp;

class EvtEvalHelAmp{

public:

  EvtEvalHelAmp(EvtId idA,
                EvtId idB,
                EvtId idC,
                EvtComplexPtrPtr HBC);

  virtual ~EvtEvalHelAmp();

  double probMax();

  void evalAmp(EvtParticle *p, EvtAmp& amp); 


private:

  void fillHelicity(int* lambda2,int n,int J2, EvtId id);
  void setUpRotationMatrices(EvtParticle *p,double theta, double phi);
  void applyRotationMatrices();

  //spins states available for particle A, B, and C.
  int _nA,_nB,_nC;

  //helicity amplitudes
  EvtComplexPtrPtr _HBC;

  //2 times spin for each of the particles
  int _JA2,_JB2,_JC2;

  //2 times the helicity for the states
  int *_lambdaA2,*_lambdaB2,*_lambdaC2;

  //Rotation matrices
  EvtComplexPtrPtr _RA,_RB,_RC;

  //temporary array for amplitudes
  EvtComplexPtrPtrPtr _amp,_amp1,_amp3;

};

#endif