include/EvtGenModels/EvtEtaLLPiPi.hh

0001
0002 /***********************************************************************
0003 * Copyright 1998-2020 CERN for the benefit of the EvtGen authors       *
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0020
0021 #ifndef EVT_ETALLPIPI_HH
0022 #define EVT_ETALLPIPI_HH
0023
0024 #include "EvtGenBase/EvtConst.hh"
0025 #include "EvtGenBase/EvtDecayProb.hh"
0026
0027 #include <string>
0028
0029 class EvtParticle;
0030
0031 // eta' -> mu+ mu- pi+ pi- or e+ e- pi+ pi-
0032 // From Zhang Zhen-Yu et al, Chinese Phys. C 36, p926, 2012
0033
0034 class EvtEtaLLPiPi : public EvtDecayProb {
0035   public:
0036     EvtEtaLLPiPi() = default;
0037
0038     void init() override;
0039     void initProbMax() override;
0040
0041     std::string getName() override;
0042     EvtDecayBase* clone() override;
0043
0044     void decay( EvtParticle* p ) override;
0045
0046   private:
0047     void updateMassPars( double mLep, double mPi );
0048
0049     double rhoWidth( double s, double m ) const;
0050
0051     double F0( double sLL, double sPiPi ) const;
0052
0053     double lambda( double a, double b, double c ) const;
0054
0055     double ampSquared( EvtParticle* p ) const;
0056
0057     double m_alpha{ 1.0 / 137.0 };
0058     double m_eSq{ 4.0 * EvtConst::pi * m_alpha };
0059     double m_fPi{ 0.0924 };
0060     double m_f8{ 1.3 * m_fPi };
0061     double m_f0{ 1.04 * m_fPi };
0062     double m_thetaMix{ 20.0 * EvtConst::pi / 180.0 };
0063     double m_mixSq{ 0.0 };
0064     double m_c1{ 1.0 };
0065     double m_c2{ 0.0 };
0066     double m_c3{ m_c1 - m_c2 };    // Eq 9
0067     double m_par1{ 1.0 - ( 3.0 * ( m_c1 - m_c2 + m_c3 ) / 4.0 ) };
0068     double m_parLL{ 3.0 * ( m_c1 - m_c2 - m_c3 ) / 4.0 };
0069     double m_parPiPi{ 3.0 * m_c3 / 2.0 };
0070     double m_rhoMass{ 0.775 };    // updated in init()
0071     double m_rhoMassSq{ m_rhoMass * m_rhoMass };
0072     double m_rhoGamma{ 0.149 };    // updated in init()
0073     double m_lepMass{ 0.106 };     // modified in updateMassPars()
0074     double m_lepMassSq{ m_lepMass * m_lepMass };
0075     double m_piMass{ 0.140 };    // modified in updateMassPars()
0076     double m_piMassSq{ m_piMass * m_piMass };
0077     double m_4LepMassSq{ 4.0 * m_lepMassSq };
0078     double m_4PiMassSq{ 4.0 * m_piMassSq };
0079 };
0080
0081 #endif