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EvtResonance.cpp
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EvtResonance.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/EvtResonance.hh"
#include "EvtGenBase/EvtComplex.hh"
#include "EvtGenBase/EvtConst.hh"
#include "EvtGenBase/EvtKine.hh"
#include "EvtGenBase/EvtPatches.hh"
#include "EvtGenBase/EvtReport.hh"
#include "EvtGenBase/EvtVector4R.hh"
#include <math.h>
using std::endl;
EvtResonance& EvtResonance::operator=( const EvtResonance& n )
{
if ( &n == this )
return *this;
_p4_p = n._p4_p;
_p4_d1 = n._p4_d1;
_p4_d2 = n._p4_d2;
_ampl = n._ampl;
_theta = n._theta;
_gamma = n._gamma;
_spin = n._spin;
_bwm = n._bwm;
return *this;
}
EvtResonance::EvtResonance( const EvtVector4R& p4_p, const EvtVector4R& p4_d1,
const EvtVector4R& p4_d2, double ampl, double theta,
double gamma, double bwm, int spin ) :
_p4_p( p4_p ),
_p4_d1( p4_d1 ),
_p4_d2( p4_d2 ),
_ampl( ampl ),
_theta( theta ),
_gamma( gamma ),
_bwm( bwm ),
_spin( spin )
{
}
EvtComplex EvtResonance::resAmpl()
{
double pi180inv = 1.0 / EvtConst::radToDegrees;
EvtComplex ampl;
//EvtVector4R _p4_d3 = _p4_p-_p4_d1-_p4_d2;
//get cos of the angle between the daughters from their 4-momenta
//and the 4-momentum of the parent
//in general, EvtDecayAngle(parent, part1+part2, part1) gives the angle
//the missing particle (not listed in the arguments) makes
//with part2 in the rest frame of both
//listed particles (12)
//angle 3 makes with 2 in rest frame of 12 (CS3)
double cos_phi_0 = EvtDecayAngle( _p4_p, _p4_d1 + _p4_d2, _p4_d1 );
//angle 3 makes with 1 in 12 is, of course, -cos_phi_0
switch ( _spin ) {
case 0:
ampl = ( _ampl *
EvtComplex( cos( _theta * pi180inv ),
sin( _theta * pi180inv ) ) *
sqrt( _gamma / EvtConst::twoPi ) *
( 1.0 / ( ( _p4_d1 + _p4_d2 ).mass() - _bwm -
EvtComplex( 0.0, 0.5 * _gamma ) ) ) );
break;
case 1:
ampl = ( _ampl *
EvtComplex( cos( _theta * pi180inv ),
sin( _theta * pi180inv ) ) *
sqrt( _gamma / EvtConst::twoPi ) *
( cos_phi_0 / ( ( _p4_d1 + _p4_d2 ).mass() - _bwm -
EvtComplex( 0.0, 0.5 * _gamma ) ) ) );
break;
case 2:
ampl = ( _ampl *
EvtComplex( cos( _theta * pi180inv ),
sin( _theta * pi180inv ) ) *
sqrt( _gamma / EvtConst::twoPi ) *
( ( 1.5 * cos_phi_0 * cos_phi_0 - 0.5 ) /
( ( _p4_d1 + _p4_d2 ).mass() - _bwm -
EvtComplex( 0.0, 0.5 * _gamma ) ) ) );
break;
case 3:
ampl = ( _ampl *
EvtComplex( cos( _theta * pi180inv ),
sin( _theta * pi180inv ) ) *
sqrt( _gamma / EvtConst::twoPi ) *
( ( 2.5 * cos_phi_0 * cos_phi_0 * cos_phi_0 -
1.5 * cos_phi_0 ) /
( ( _p4_d1 + _p4_d2 ).mass() - _bwm -
EvtComplex( 0.0, 0.5 * _gamma ) ) ) );
break;
default:
EvtGenReport( EVTGEN_DEBUG, "EvtGen" )
<< "EvtGen: wrong spin in EvtResonance" << endl;
ampl = EvtComplex( 0.0 );
break;
}
return ampl;
}
EvtComplex EvtResonance::relBrWig( int i )
{
//this function returns relativistic Breit-Wigner amplitude
//for a given resonance (for P-wave decays of scalars only at the moment!)
EvtComplex BW;
EvtVector4R _p4_d3 = _p4_p - _p4_d1 - _p4_d2;
EvtVector4R _p4_12 = _p4_d1 + _p4_d2;
double msq13 = ( _p4_d1 + _p4_d3 ).mass2();
double msq23 = ( _p4_d2 + _p4_d3 ).mass2();
double msqParent = _p4_p.mass2();
double msq1 = _p4_d1.mass2();
double msq2 = _p4_d2.mass2();
double msq3 = _p4_d3.mass2();
double M;
double p2 = sqrt( ( _p4_12.mass2() - ( _p4_d1.mass() + _p4_d2.mass() ) *
( _p4_d1.mass() + _p4_d2.mass() ) ) *
( _p4_12.mass2() - ( _p4_d1.mass() - _p4_d2.mass() ) *
( _p4_d1.mass() - _p4_d2.mass() ) ) ) /
( 2.0 * _p4_12.mass() );
double p2R = sqrt( ( _bwm * _bwm - ( _p4_d1.mass() + _p4_d2.mass() ) *
( _p4_d1.mass() + _p4_d2.mass() ) ) *
( _bwm * _bwm - ( _p4_d1.mass() - _p4_d2.mass() ) *
( _p4_d1.mass() - _p4_d2.mass() ) ) ) /
( 2.0 * _bwm );
double gam, R;
if ( i == 1 ) {
R = 2.0 / ( 0.197 );
} else
R = 5.0 / ( 0.197 );
gam = _gamma * ( _bwm / _p4_12.mass() ) * ( p2 / p2R ) * ( p2 / p2R ) *
( p2 / p2R ) * ( ( 1 + R * R * p2R * p2R ) / ( 1 + R * R * p2 * p2 ) );
M = ( msq13 - msq23 -
( msqParent - msq3 ) * ( msq1 - msq2 ) / ( _bwm * _bwm ) ) *
sqrt( ( 1 + R * R * p2R * p2R ) / ( 1 + R * R * p2 * p2 ) );
BW = sqrt( _gamma ) * M /
( ( _bwm * _bwm - _p4_12.mass2() ) -
EvtComplex( 0.0, 1.0 ) * gam * _bwm );
return BW;
}

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