EvtHighSpinParticle.cpp

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#include "EvtGenBase/EvtHighSpinParticle.hh"

#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtPatches.hh"
#include "EvtGenBase/EvtSpinDensity.hh"
#include "EvtGenBase/EvtVector4R.hh"
#include "EvtGenBase/EvtdFunction.hh"

#include <assert.h>
#include <iostream>
#include <math.h>

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

    setLifetime();
}

EvtSpinDensity EvtHighSpinParticle::rotateToHelicityBasis() const
{
    int n = EvtSpinType::getSpinStates( EvtPDL::getSpinType( getId() ) );

    EvtSpinDensity R;
    R.setDiag( n );

    return R;
}

EvtSpinDensity EvtHighSpinParticle::rotateToHelicityBasis( double alpha,
                                                           double beta,
                                                           double gamma ) const
{
    int i, j;

    int n = EvtSpinType::getSpinStates( EvtPDL::getSpinType( getId() ) );

    EvtSpinDensity R;

    R.setDim( n );

    int J2 = EvtSpinType::getSpin2( EvtPDL::getSpinType( getId() ) );

    assert( n == J2 + 1 );

    auto lambda2 = [J2]( int i ) { return J2 - i * 2; };

    for ( i = 0; i < n; i++ ) {
        for ( j = 0; j < n; j++ ) {
            R.set( i, j,
                   EvtdFunction::d( J2, lambda2( j ), lambda2( i ), beta ) *
                       exp( EvtComplex( 0.0, 0.5 * ( alpha * lambda2( i ) -
                                                     gamma * lambda2( j ) ) ) ) );
        }
    }

    return R;
}