EvtDiracParticle.cpp

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#include "EvtGenBase/EvtDiracParticle.hh"

#include "EvtGenBase/EvtComplex.hh"
#include "EvtGenBase/EvtGammaMatrix.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtPatches.hh"
#include "EvtGenBase/EvtReport.hh"
#include "EvtGenBase/EvtSpinDensity.hh"
#include "EvtGenBase/EvtVector4R.hh"

#include <iostream>
#include <math.h>
#include <stdlib.h>
using std::endl;

void EvtDiracParticle::init( EvtId part_n, const EvtVector4R& p4 )
{
    _validP4 = true;
    setp( p4 );
    setpart_num( part_n );

    if ( EvtPDL::getStdHep( part_n ) == 0 ) {
        EvtGenReport( EVTGEN_ERROR, "EvtGen" )
            << "Error in EvtDiracParticle::init, part_n=" << part_n.getId()
            << endl;
        ::abort();
    }

    if ( EvtPDL::getStdHep( part_n ) > 0 ) {
        _spinorRest[0].set( EvtComplex( sqrt( 2.0 * mass() ), 0.0 ),
                            EvtComplex( 0.0, 0.0 ), EvtComplex( 0.0, 0.0 ),
                            EvtComplex( 0.0, 0.0 ) );
        _spinorRest[1].set( EvtComplex( 0.0, 0.0 ),
                            EvtComplex( sqrt( 2.0 * mass() ), 0.0 ),
                            EvtComplex( 0.0, 0.0 ), EvtComplex( 0.0, 0.0 ) );

        _spinorParent[0] = boostTo( _spinorRest[0], p4 );
        _spinorParent[1] = boostTo( _spinorRest[1], p4 );

    } else {
        _spinorRest[0].set( EvtComplex( 0.0, 0.0 ), EvtComplex( 0.0, 0.0 ),
                            EvtComplex( sqrt( 2.0 * mass() ), 0.0 ),
                            EvtComplex( 0.0, 0.0 ) );
        _spinorRest[1].set( EvtComplex( 0.0, 0.0 ), EvtComplex( 0.0, 0.0 ),
                            EvtComplex( 0.0, 0.0 ),
                            EvtComplex( sqrt( 2.0 * mass() ), 0.0 ) );

        _spinorParent[0] = boostTo( _spinorRest[0], p4 );
        _spinorParent[1] = boostTo( _spinorRest[1], p4 );
    }

    setLifetime();
}

void EvtDiracParticle::init( EvtId part_n, const EvtVector4R& p4,
                             const EvtDiracSpinor& prod1,
                             const EvtDiracSpinor& prod2,
                             const EvtDiracSpinor& rest1,
                             const EvtDiracSpinor& rest2 )
{
    _validP4 = true;
    setp( p4 );
    setpart_num( part_n );

    if ( EvtPDL::getStdHep( part_n ) == 0 ) {
        EvtGenReport( EVTGEN_ERROR, "EvtGen" )
            << "Error in EvtDiracParticle::init, part_n=" << part_n.getId()
            << std::endl;
        ::abort();
    }
    _spinorRest[0] = rest1;
    _spinorRest[1] = rest2;
    _spinorParent[0] = prod1;
    _spinorParent[1] = prod2;

    setLifetime();
}

EvtSpinDensity EvtDiracParticle::rotateToHelicityBasis() const
{
    EvtDiracSpinor spplus;
    EvtDiracSpinor spminus;

    double sqmt2 = sqrt( 2. * ( getP4().mass() ) );

    if ( EvtPDL::getStdHep( getId() ) > 0 ) {
        spplus.set( 1.0, 0.0, 0.0, 0.0 );
        spminus.set( 0.0, 1.0, 0.0, 0.0 );
    } else {
        spplus.set( 0.0, 0.0, 1.0, 0.0 );
        spminus.set( 0.0, 0.0, 0.0, 1.0 );
    }

    EvtSpinDensity R;
    R.setDim( 2 );

    for ( int i = 0; i < 2; i++ ) {
        R.set( 0, i, ( spplus * _spinorRest[i] ) / sqmt2 );
        R.set( 1, i, ( spminus * _spinorRest[i] ) / sqmt2 );
    }

    return R;
}

EvtSpinDensity EvtDiracParticle::rotateToHelicityBasis( double alpha, double beta,
                                                        double gamma ) const
{
    EvtDiracSpinor spplus;
    EvtDiracSpinor spminus;

    double sqmt2 = sqrt( 2. * ( getP4().mass() ) );

    if ( EvtPDL::getStdHep( getId() ) > 0 ) {
        spplus.set( 1.0, 0.0, 0.0, 0.0 );
        spminus.set( 0.0, 1.0, 0.0, 0.0 );
    } else {
        spplus.set( 0.0, 0.0, 1.0, 0.0 );
        spminus.set( 0.0, 0.0, 0.0, 1.0 );
    }

    spplus.applyRotateEuler( alpha, beta, gamma );
    spminus.applyRotateEuler( alpha, beta, gamma );

    EvtSpinDensity R;
    R.setDim( 2 );

    for ( int i = 0; i < 2; i++ ) {
        R.set( 0, i, ( spplus * _spinorRest[i] ) / sqmt2 );
        R.set( 1, i, ( spminus * _spinorRest[i] ) / sqmt2 );
    }

    return R;
}