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EvtBlattWeisskopf.cpp
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EvtBlattWeisskopf.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/EvtBlattWeisskopf.hh"
#include "EvtGenBase/EvtPatches.hh"
#include "EvtGenBase/EvtReport.hh"
#include <assert.h>
#include <iostream>
#include <math.h>
using std::endl;
EvtBlattWeisskopf::EvtBlattWeisskopf( int LL, double R, double p0 ) :
_LL( LL ), _radial( R ), _p0( p0 )
{
if ( R < 0 ) {
EvtGenReport( EVTGEN_INFO, "EvtGen" )
<< "Radius " << R << " negative" << endl;
assert( 0 );
}
_radial = R;
// compute formula for nominal momentum
_F0 = compute( _p0 );
if ( _F0 <= 0 ) {
EvtGenReport( EVTGEN_INFO, "EvtGen" )
<< "Invalid nominal form factor computed " << _F0 << endl;
assert( 0 );
}
}
EvtBlattWeisskopf::EvtBlattWeisskopf( const EvtBlattWeisskopf& other ) :
_LL( other._LL ), _radial( other._radial ), _p0( other._p0 ), _F0( other._F0 )
{
}
double EvtBlattWeisskopf::operator()( double p ) const
{
double ret = compute( p ) / _F0;
// EvtGenReport(EVTGEN_INFO,"EvtGen") << p << " " << _p0 << " " << _F0 << " " << _LL << " " << _radial << " " << ret << endl;
return ret;
}
// Blatt-Weisskopf form factors
// see e.g. hep-ex/0011065
// Dalitz Analysis of the Decay D0->K-pi+pi0 (CLEO)
//
// p - momentum of either daugher in the meson rest frame,
// the mass of the meson is used
// pAB - momentum of either daughter in the candidate rest frame
// the mass of the candidate is used
// R - meson radial parameter
//
// In the CLEO paper R=5 GeV-1 for D0, R=1.5 for intermediate resonances
double EvtBlattWeisskopf::compute( double p ) const
{
double value( 1.0 );
double z = p * _radial;
double zSq = z * z;
if ( _LL == 0 ) {
value = 1.0;
} else if ( _LL == 1 ) {
value = sqrt( 1.0 / ( 1.0 + zSq ) );
} else if ( _LL == 2 ) {
value = sqrt( 1.0 / ( zSq * ( zSq + 3.0 ) + 9.0 ) );
} else if ( _LL == 3 ) {
double denom = zSq * ( zSq * ( zSq + 6.0 ) + 45.0 ) + 225.0;
value = sqrt( 1.0 / denom );
} else if ( _LL == 4 ) {
double denom = zSq * ( zSq * ( zSq * ( zSq + 10.0 ) + 135.0 ) + 1575.0 ) +
11025.0;
value = sqrt( 1.0 / denom );
} else if ( _LL == 5 ) {
double denom =
zSq * ( zSq * ( zSq * ( zSq * ( zSq + 15.0 ) + 315.0 ) + 6300.0 ) +
99225.0 ) +
893025.0;
value = sqrt( 1.0 / denom );
}
return value;
}

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