EvtBLLNuLAmp.hh

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#ifndef EVTBLLNUL_AMP_HH
#define EVTBLLNUL_AMP_HH

#include "EvtGenBase/EvtAmp.hh"
#include "EvtGenBase/EvtComplex.hh"
#include "EvtGenBase/EvtId.hh"
#include "EvtGenBase/EvtTensor4C.hh"
#include "EvtGenBase/EvtVector4R.hh"

#include <vector>

class EvtParticle;

// Description: Header file for the amplitude calculation for the "BLLNUL"
//              model which generates rare four-leptonic B-decays
//              B^-(p) -> ell^+(k_1) ell^-(k_2) neu (k_3) ell^-(k_4)

class EvtBLLNuLAmp {
  public:
    EvtBLLNuLAmp( double Vub = 4.09e-3 );
    EvtBLLNuLAmp( double qSqMin, double kSqMin, bool symmetry,
                  double Vub = 4.09e-3 );

    void CalcAmp( EvtParticle* parent, EvtAmp& amp ) const;
    void setParameters( double qSqMin, double kSqMin, bool symmetry );

    // Resonance poles
    class ResPole final {
      public:
        ResPole( double mass, double width, double coupling );

        EvtComplex propagator( double qSq, int numForm = 0 ) const;

        double getMass() const { return m0_; }
        double getMassSq() const { return m0Sq_; }
        double getWidth() const { return w0_; }
        double getCoupling() const { return c_; }

      private:
        double m0_;    // pole mass
        double m0Sq_;
        double w0_;    // width
        double c_;     // coupling constant
        EvtComplex I_;
        EvtComplex Imw_;
    };

  protected:
    EvtTensor4C getHadronTensor( const EvtVector4R& q, const EvtVector4R& k,
                                 const double qSq, const double kSq,
                                 const double MB, const int sign ) const;

    std::vector<EvtComplex> getVMDTerms( double qSq, double kSq, double MB ) const;

    EvtComplex getBStarTerm( double qSq, double kSq, double MB ) const;

    double FF_B2Bstar( double qSq ) const;

    double FF_V( double kSq ) const;

    double FF_A1( double kSq ) const;

    double FF_A2( double kSq ) const;

  private:
    // Kinematic cut-offs
    double qSqMin_;
    double kSqMin_;

    // If we have identical charged lepton flavours
    bool symmetry_;

    // B+, B- Ids
    EvtId BpId_, BnId_;

    // Form factor constants
    double coupling_, sqrt2_;
    double fBu_;

    // Resonance poles
    EvtBLLNuLAmp::ResPole Bstar_, Upsilon_;

    std::vector<EvtBLLNuLAmp::ResPole> resPoles_;
    int nPoles_;

    // Complex number constants
    EvtComplex zero_, unitI_;
};

inline void EvtBLLNuLAmp::setParameters( double qSqMin, double kSqMin,
                                         bool symmetry )
{
    qSqMin_ = qSqMin;
    kSqMin_ = kSqMin;
    symmetry_ = symmetry;
}

#endif