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EvtEtaLLPiPi.hh
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/***********************************************************************
* Copyright 1998-2020 CERN for the benefit of the EvtGen authors *
* *
* This file is part of EvtGen. *
* *
* EvtGen is free software: you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation, either version 3 of the License, or *
* (at your option) any later version. *
* *
* EvtGen is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU General Public License for more details. *
* *
* You should have received a copy of the GNU General Public License *
* along with EvtGen. If not, see <https://www.gnu.org/licenses/>. *
***********************************************************************/
#ifndef EVT_ETALLPIPI_HH
#define EVT_ETALLPIPI_HH
#include "EvtGenBase/EvtConst.hh"
#include "EvtGenBase/EvtDecayProb.hh"
#include <string>
class EvtParticle;
// eta' -> mu+ mu- pi+ pi- or e+ e- pi+ pi-
// From Zhang Zhen-Yu et al, Chinese Phys. C 36, p926, 2012
class EvtEtaLLPiPi : public EvtDecayProb {
public:
EvtEtaLLPiPi() = default;
void init() override;
void initProbMax() override;
std::string getName() const override;
EvtDecayBase* clone() const override;
void decay( EvtParticle* p ) override;
private:
void updateMassPars( double mLep, double mPi );
double rhoWidth( double s, double m ) const;
double F0( double sLL, double sPiPi ) const;
double lambda( double a, double b, double c ) const;
double ampSquared( EvtParticle* p ) const;
double m_alpha{ 1.0 / 137.0 };
double m_eSq{ 4.0 * EvtConst::pi * m_alpha };
double m_fPi{ 0.0924 };
double m_f8{ 1.3 * m_fPi };
double m_f0{ 1.04 * m_fPi };
double m_thetaMix{ 20.0 * EvtConst::pi / 180.0 };
double m_mixSq{ 0.0 };
double m_c1{ 1.0 };
double m_c2{ 0.0 };
double m_c3{ m_c1 - m_c2 }; // Eq 9
double m_par1{ 1.0 - ( 3.0 * ( m_c1 - m_c2 + m_c3 ) / 4.0 ) };
double m_parLL{ 3.0 * ( m_c1 - m_c2 - m_c3 ) / 4.0 };
double m_parPiPi{ 3.0 * m_c3 / 2.0 };
double m_rhoMass{ 0.775 }; // updated in init()
double m_rhoMassSq{ m_rhoMass * m_rhoMass };
double m_rhoGamma{ 0.149 }; // updated in init()
double m_lepMass{ 0.106 }; // modified in updateMassPars()
double m_lepMassSq{ m_lepMass * m_lepMass };
double m_piMass{ 0.140 }; // modified in updateMassPars()
double m_piMassSq{ m_piMass * m_piMass };
double m_4LepMassSq{ 4.0 * m_lepMassSq };
double m_4PiMassSq{ 4.0 * m_piMassSq };
};
#endif

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