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EvtPropFlatte.cpp
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EvtPropFlatte.cpp
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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/>. *
***********************************************************************/
#include "EvtGenBase/EvtPropFlatte.hh"
#include "EvtGenBase/EvtPatches.hh"
#include <iostream>
#include <math.h>
using std::cout;
using std::endl;
EvtPropFlatte::EvtPropFlatte( double m0, double g0, double m0a, double m0b,
double g1, double m1a, double m1b ) :
EvtPropagator( m0, g0 ),
_m0a( m0a ),
_m0b( m0b ),
_g1( g1 ),
_m1a( m1a ),
_m1b( m1b )
{
}
EvtAmplitude<EvtPoint1D>* EvtPropFlatte::clone() const
{
return new EvtPropFlatte( *this );
}
EvtComplex EvtPropFlatte::amplitude( const EvtPoint1D& x ) const
{
/*
Use BES parameterization:
1.
-----------------------------------------
m0^2 - m^2 - i*m0*( g1*rho1 + g2*rho2 )
Resonance mass: m0
Channel1: m0a, m0b, g0
Channel2: m1a, m1b, g1
where breakup momenta q's are:
E0a = (m^2 + m0a^2 - m0b^2) / 2m
q0 = sqrt( E0a^2 - m0a^2 )
E1a = (m^2 + m1a^2 - m1b^2) / 2m
q1 = sqrt( E1a^2 - m1a^2 )
*/
double s = x.value() * x.value();
double m = x.value();
double E0a = 0.5 * ( s + _m0a * _m0a - _m0b * _m0b ) / m;
double qSq0 = E0a * E0a - _m0a * _m0a;
double E1a = 0.5 * ( s + _m1a * _m1a - _m1b * _m1b ) / m;
double qSq1 = E1a * E1a - _m1a * _m1a;
EvtComplex gamma0 = qSq0 >= 0 ? EvtComplex( _g0 * sqrt( qSq0 ), 0 )
: EvtComplex( 0, _g0 * sqrt( -qSq0 ) );
EvtComplex gamma1 = qSq1 >= 0 ? EvtComplex( _g1 * sqrt( qSq1 ), 0 )
: EvtComplex( 0, _g1 * sqrt( -qSq1 ) );
EvtComplex gamma = gamma0 + gamma1;
EvtComplex a = 1.0 /
( _m0 * _m0 - s - EvtComplex( 0.0, 2 * _m0 / m ) * gamma );
return a;
}

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