EvtRareLbToLllFFGutsche.cpp

Go to the documentation of this file.

/***********************************************************************
* 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 "EvtGenModels/EvtRareLbToLllFFGutsche.hh"

#include "EvtGenBase/EvtIdSet.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtVector4R.hh"

//-----------------------------------------------------------------------------
// Implementation file for class : EvtRareLbToLllFFGutsche
//
// 2014-10-21 : Michal Kreps
//-----------------------------------------------------------------------------

//=============================================================================
// Standard constructor, initializes variables
//=============================================================================

EvtIdSet EvtRareLbToLllFFGutsche::fParents( "Lambda_b0", "anti-Lambda_b0" );
EvtIdSet EvtRareLbToLllFFGutsche::fDaughters( "Lambda0", "anti-Lambda0" );

void EvtRareLbToLllFFGutsche::init()
{
    fVconsts[0][0] = 0.107;
    fVconsts[0][1] = 2.27;
    fVconsts[0][2] = 1.367;
    fVconsts[1][0] = 0.043;
    fVconsts[1][1] = 2.411;
    fVconsts[1][2] = 1.531;
    fVconsts[2][0] = -0.003;
    fVconsts[2][1] = 2.815;
    fVconsts[2][2] = 2.041;

    fAconsts[0][0] = 0.104;
    fAconsts[0][1] = 2.232;
    fAconsts[0][2] = 1.328;
    fAconsts[1][0] = -0.003;
    fAconsts[1][1] = 2.955;
    fAconsts[1][2] = 3.620;
    fAconsts[2][0] = -0.052;
    fAconsts[2][1] = 2.437;
    fAconsts[2][2] = 1.559;

    fTVconsts[0][0] = -0.043;
    fTVconsts[0][1] = 2.411;
    fTVconsts[0][2] = 1.531;
    fTVconsts[1][0] = -0.105;
    fTVconsts[1][1] = 2.27118;
    fTVconsts[1][2] = 1.36776;
    fTVconsts[2][0] = 0;    // Not used anywhere
    fTVconsts[2][1] = 0;
    fTVconsts[2][2] = 0;

    fTAconsts[0][0] = 0.003;
    fTAconsts[0][1] = 2.955;
    fTAconsts[0][2] = 3.620;
    fTAconsts[1][0] = -0.105;
    fTAconsts[1][1] = 2.233;
    fTAconsts[1][2] = 1.328;
    fTAconsts[2][0] = 0;    // Not used anywhere
    fTAconsts[2][1] = 0;
    fTAconsts[2][2] = 0;

    EvtGenReport( EVTGEN_INFO, "EvtGen" )
        << " EvtRareLbToLll is using form factors from arXiv:1301.3737 "
        << std::endl;
}

//=============================================================================

void EvtRareLbToLllFFGutsche::getFF( EvtParticle* parent, EvtParticle* lambda,
                                     EvtRareLbToLllFFBase::FormFactors& FF )
{
    // Find the FF information for this particle, start by setting all to zero
    FF.areZero();

    /*
  if ( ! ( fParents.contains(parent->getId()) &&
           fDaughters.contains(lambda->getId()) ) )
  {
    EvtGenReport(EVTGEN_ERROR,"EvtGen") << " EvtRareLbToLllFFGutsche: Unknown mother and/or daughter. " << std::endl;
    return;
  }
*/

    double m1 = parent->getP4().mass();
    double m2 = lambda->getP4().mass();
    EvtVector4R p4parent;
    p4parent.set( parent->mass(), 0, 0, 0 );
    double q2 = ( p4parent - lambda->getP4() ).mass2();
    double m21 = m2 / m1;
    double shat = q2 / m1 / m1;

    double fV[3];
    double fA[3];
    for ( int i = 0; i <= 2; ++i ) {
        fV[i] = formFactorParametrization( shat, fVconsts[i][0], fVconsts[i][1],
                                           fVconsts[i][2] );
        fA[i] = formFactorParametrization( shat, fAconsts[i][0], fAconsts[i][1],
                                           fAconsts[i][2] );
    }
    double fTV[2];
    double fTA[2];
    for ( int i = 0; i <= 1; ++i ) {
        fTV[i] = formFactorParametrization( shat, fTVconsts[i][0],
                                            fTVconsts[i][1], fTVconsts[i][2] );
        fTA[i] = formFactorParametrization( shat, fTAconsts[i][0],
                                            fTAconsts[i][1], fTAconsts[i][2] );
    }

    // Both v^2==v'^2==1 by definition
    FF.F_[0] = fV[0] + fV[1] * ( 1 + m21 );
    FF.F_[1] = fV[2] - fV[1];
    FF.F_[2] = -m21 * ( fV[1] + fV[2] );

    FF.G_[0] = fA[0] - fA[1] * ( 1 - m21 );
    FF.G_[1] = fA[2] - fA[1];
    FF.G_[2] = -m21 * ( +fA[1] + fA[2] );

    FF.FT_[0] = fTV[1] * ( m1 + m2 ) + fTV[0] * ( q2 / m1 );
    FF.FT_[1] = +fTV[0] * ( m2 - m1 ) - fTV[1] * m1;
    FF.FT_[2] = m2 * ( fTV[0] - fTV[1] ) - fTV[0] * m21 * m2;

    FF.GT_[0] = -fTA[1] * ( m1 - m2 ) + fTA[0] * ( q2 / m1 );
    FF.GT_[1] = -fTA[1] * m1 + fTA[0] * ( m1 + m2 );
    FF.GT_[2] = -fTA[0] * m2 * m21 - m2 * ( fTA[0] + fTA[1] );

    return;
}

double EvtRareLbToLllFFGutsche::formFactorParametrization( double s, double f0,
                                                           double a, double b )
{
    return f0 / ( 1 - a * s + b * s * s );
}