EvtBlattWeisskopf.cpp

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#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;
}