EvtVSSBMixCPT.cpp

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#include "EvtGenModels/EvtVSSBMixCPT.hh"
 
#include "EvtGenBase/EvtConst.hh"
#include "EvtGenBase/EvtGenKine.hh"
#include "EvtGenBase/EvtId.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtRandom.hh"
#include "EvtGenBase/EvtReport.hh"
#include "EvtGenBase/EvtVector4C.hh"
 
#include <stdlib.h>
#include <string>
using std::endl;
 
std::string EvtVSSBMixCPT::getName() const
{
    return "VSS_BMIX";
}
 
EvtDecayBase* EvtVSSBMixCPT::clone() const
{
    return new EvtVSSBMixCPT;
}
 
void EvtVSSBMixCPT::init()
{
    if ( getNArg() > 4 )
        checkNArg( 14, 12, 8 );
 
    if ( getNArg() < 1 ) {
        EvtGenReport( EVTGEN_ERROR, "EvtGen" )
            << "EvtVSSBMix generator expected "
            << " at least 1 argument (deltam) but found:" << getNArg() << endl;
        EvtGenReport( EVTGEN_ERROR, "EvtGen" )
            << "Will terminate execution!" << endl;
        ::abort();
    }
    // check that we are asked to produced exactly 2 daughters
    //4 are allowed if they are aliased..
    checkNDaug( 2, 4 );
 
    if ( getNDaug() == 4 ) {
        if ( getDaug( 0 ) != getDaug( 2 ) || getDaug( 1 ) != getDaug( 3 ) ) {
            EvtGenReport( EVTGEN_ERROR, "EvtGen" )
                << "EvtVSSBMixCPT generator allows "
                << " 4 daughters only if 1=3 and 2=4"
                << " (but 3 and 4 are aliased " << endl;
            EvtGenReport( EVTGEN_ERROR, "EvtGen" )
                << "Will terminate execution!" << endl;
            ::abort();
        }
    }
    // check that we are asked to decay a vector particle into a pair
    // of scalar particles
 
    checkSpinParent( EvtSpinType::VECTOR );
 
    checkSpinDaughter( 0, EvtSpinType::SCALAR );
    checkSpinDaughter( 1, EvtSpinType::SCALAR );
 
    // check that our daughter particles are charge conjugates of each other
    if ( !( EvtPDL::chargeConj( getDaug( 0 ) ) == getDaug( 1 ) ) ) {
        EvtGenReport( EVTGEN_ERROR, "EvtGen" )
            << "EvtVSSBMixCPT generator expected daughters "
            << "to be charge conjugate." << endl
            << "  Found " << EvtPDL::name( getDaug( 0 ) ).c_str() << " and "
            << EvtPDL::name( getDaug( 1 ) ).c_str() << endl;
        EvtGenReport( EVTGEN_ERROR, "EvtGen" )
            << "Will terminate execution!" << endl;
        ::abort();
    }
    // check that both daughter particles have the same lifetime
    if ( EvtPDL::getctau( getDaug( 0 ) ) != EvtPDL::getctau( getDaug( 1 ) ) ) {
        EvtGenReport( EVTGEN_ERROR, "EvtGen" )
            << "EvtVSSBMixCPT generator expected daughters "
            << "to have the same lifetime." << endl
            << "  Found ctau = " << EvtPDL::getctau( getDaug( 0 ) )
            << " mm and " << EvtPDL::getctau( getDaug( 1 ) ) << " mm" << endl;
        EvtGenReport( EVTGEN_ERROR, "EvtGen" )
            << "Will terminate execution!" << endl;
        ::abort();
    }
    // precompute quantities that will be used to generate events
    // and print out a summary of parameters for this decay
 
    // mixing frequency in hbar/mm
    m_freq = getArg( 0 ) / EvtConst::c;
 
    // deltaG
    double gamma = 1 / EvtPDL::getctau( getDaug( 0 ) );    // gamma/c (1/mm)
    m_dGamma = 0.0;
    double dgog = 0.0;
    if ( getNArg() > 1 ) {
        dgog = getArg( 1 );
        m_dGamma = dgog * gamma;
    }
    // q/p
    m_qoverp = EvtComplex( 1.0, 0.0 );
    if ( getNArg() > 2 ) {
        m_qoverp = EvtComplex( getArg( 2 ), 0.0 );
    }
    if ( getNArg() > 3 ) {
        m_qoverp = getArg( 2 ) *
                   EvtComplex( cos( getArg( 3 ) ), sin( getArg( 3 ) ) );
    }
    m_poverq = 1.0 / m_qoverp;
 
    // decay amplitudes
    m_A_f = EvtComplex( 1.0, 0.0 );
    m_Abar_f = EvtComplex( 0.0, 0.0 );
    m_A_fbar = m_Abar_f;    // CPT conservation
    m_Abar_fbar = m_A_f;    // CPT conservation
    if ( getNArg() > 4 ) {
        m_A_f = getArg( 4 ) *
                EvtComplex( cos( getArg( 5 ) ),
                            sin( getArg( 5 ) ) );    // this allows for DCSD
        m_Abar_f = getArg( 6 ) *
                   EvtComplex( cos( getArg( 7 ) ),
                               sin( getArg( 7 ) ) );    // this allows for DCSD
        if ( getNArg() > 8 ) {
            // CPT violation in decay
            m_A_fbar = getArg( 8 ) *
                       EvtComplex( cos( getArg( 9 ) ), sin( getArg( 9 ) ) );
            m_Abar_fbar = getArg( 10 ) * EvtComplex( cos( getArg( 11 ) ),
                                                     sin( getArg( 11 ) ) );
        } else {
            // CPT conservation in decay
            m_A_fbar = m_Abar_f;
            m_Abar_fbar = m_A_f;
        }
    }
 
    // CPT violation in mixing
    m_z = EvtComplex( 0.0, 0.0 );
    if ( getNArg() > 12 ) {
        m_z = EvtComplex( getArg( 12 ), getArg( 13 ) );
    }
 
    // some printout
    double tau = 1e12 * EvtPDL::getctau( getDaug( 0 ) ) / EvtConst::c;    // in ps
    double dm = 1e-12 * getArg( 0 );    // B0/anti-B0 mass difference in hbar/ps
    double x = dm * tau;
    double y = dgog * 0.5;    //y=dgamma/(2*gamma)
    double qop2 = abs( m_qoverp * m_qoverp );
    m_chib0_b0bar = qop2 * ( x * x + y * y ) /
                    ( qop2 * ( x * x + y * y ) + 2 + x * x -
                      y * y );    // does not include CPT in mixing
    m_chib0bar_b0 = ( 1 / qop2 ) * ( x * x + y * y ) /
                    ( ( 1 / qop2 ) * ( x * x + y * y ) + 2 + x * x -
                      y * y );    // does not include CPT in mixing
 
    if ( verbose() ) {
        EvtGenReport( EVTGEN_INFO, "EvtGen" )
            << "VSS_BMIXCPT will generate mixing and CPT/CP effects in mixing:"
            << endl
            << endl
            << "    " << EvtPDL::name( getParentId() ).c_str() << " --> "
            << EvtPDL::name( getDaug( 0 ) ).c_str() << " + "
            << EvtPDL::name( getDaug( 1 ) ).c_str() << endl
            << endl
            << "using parameters:" << endl
            << endl
            << "  delta(m)  = " << dm << " hbar/ps" << endl
            << "  freq      = " << m_freq << " hbar/mm" << endl
            << "  dgog      = " << dgog << endl
            << "  dGamma    = " << m_dGamma << " hbar/mm" << endl
            << "  q/p       = " << m_qoverp << endl
            << "  z         = " << m_z << endl
            << "  tau       = " << tau << " ps" << endl
            << "  x         = " << x << endl
            << " chi(B0->B0bar) = " << m_chib0_b0bar << endl
            << " chi(B0bar->B0) = " << m_chib0bar_b0 << endl
            << " Af         = " << m_A_f << endl
            << " Abarf      = " << m_Abar_f << endl
            << " Afbar      = " << m_A_fbar << endl
            << " Abarfbar   = " << m_Abar_fbar << endl
            << endl;
    }
}
 
void EvtVSSBMixCPT::initProbMax()
{
    // this value is ok for reasonable values of all the parameters
    setProbMax( 4.0 );
}
 
void EvtVSSBMixCPT::decay( EvtParticle* p )
{
    static const EvtId B0 = EvtPDL::getId( "B0" );
    static const EvtId B0B = EvtPDL::getId( "anti-B0" );
 
    // generate a final state according to phase space
 
    double rndm = EvtRandom::random();
 
    if ( getNDaug() == 4 ) {
        EvtId tempDaug[2];
 
        if ( rndm < 0.5 ) {
            tempDaug[0] = getDaug( 0 );
            tempDaug[1] = getDaug( 3 );
        } else {
            tempDaug[0] = getDaug( 2 );
            tempDaug[1] = getDaug( 1 );
        }
 
        p->initializePhaseSpace( 2, tempDaug );
    } else {    //nominal case.
        p->initializePhaseSpace( 2, getDaugs() );
    }
 
    EvtParticle *s1, *s2;
 
    s1 = p->getDaug( 0 );
    s2 = p->getDaug( 1 );
    //delete any daughters - if there are daughters, they
    //are from the initialization and will be redone later
    if ( s1->getNDaug() > 0 ) {
        s1->deleteDaughters();
    }
    if ( s2->getNDaug() > 0 ) {
        s2->deleteDaughters();
    }
 
    EvtVector4R p1 = s1->getP4();
    EvtVector4R p2 = s2->getP4();
 
    // throw a random number to decide if this final state should be mixed
    rndm = EvtRandom::random();
    int mixed = ( rndm < 0.5 ) ? 1 : 0;
 
    // if this decay is mixed, choose one of the 2 possible final states
    // with equal probability (re-using the same random number)
    if ( mixed == 1 ) {
        EvtId mixedId = ( rndm < 0.25 ) ? getDaug( 0 ) : getDaug( 1 );
        EvtId mixedId2 = mixedId;
        if ( getNDaug() == 4 && rndm < 0.25 )
            mixedId2 = getDaug( 2 );
        if ( getNDaug() == 4 && rndm > 0.25 )
            mixedId2 = getDaug( 3 );
        s1->init( mixedId, p1 );
        s2->init( mixedId2, p2 );
    }
 
    // if this decay is unmixed, choose one of the 2 possible final states
    // with equal probability (re-using the same random number)
    if ( mixed == 0 ) {
        EvtId unmixedId = ( rndm < 0.75 ) ? getDaug( 0 ) : getDaug( 1 );
        EvtId unmixedId2 = ( rndm < 0.75 ) ? getDaug( 1 ) : getDaug( 0 );
        if ( getNDaug() == 4 && rndm < 0.75 )
            unmixedId2 = getDaug( 3 );
        if ( getNDaug() == 4 && rndm > 0.75 )
            unmixedId2 = getDaug( 2 );
        s1->init( unmixedId, p1 );
        s2->init( unmixedId2, p2 );
    }
 
    // choose a decay time for each final state particle using the
    // lifetime (which must be the same for both particles) in pdt.table
    // and calculate the lifetime difference for this event
    s1->setLifetime();
    s2->setLifetime();
    double dct = s1->getLifetime() - s2->getLifetime();    // in mm
 
    // Convention: m_dGamma=GammaLight-GammaHeavy
    EvtComplex exp1( -0.25 * m_dGamma * dct, 0.5 * m_freq * dct );
 
    /*
  //Find the flavor of the B that decayed first.
  EvtId firstDec = (dct > 0 ) ? s2->getId() : s1->getId();
 
  //This tags the flavor of the other particle at that time.
  EvtId stateAtDeltaTeq0 = ( firstDec==B0 ) ? B0B : B0;
  */
    EvtId stateAtDeltaTeq0 = ( s2->getId() == B0 ) ? B0B : B0;
 
    // calculate the oscillation amplitude, based on wether this event is mixed or not
    EvtComplex osc_amp;
 
    //define some useful functions: (see BAD #188 eq. 39 for ref.)
    EvtComplex gp = 0.5 * ( exp( -1.0 * exp1 ) + exp( exp1 ) );
    EvtComplex gm = 0.5 * ( exp( -1.0 * exp1 ) - exp( exp1 ) );
    EvtComplex sqz = sqrt( abs( 1 - m_z * m_z ) ) *
                     exp( EvtComplex( 0, arg( 1 - m_z * m_z ) / 2 ) );
 
    EvtComplex BB = gp + m_z * gm;              // <B0|B0(t)>
    EvtComplex barBB = -sqz * m_qoverp * gm;    // <B0bar|B0(t)>
    EvtComplex BbarB = -sqz * m_poverq * gm;    // <B0|B0bar(t)>
    EvtComplex barBbarB = gp - m_z * gm;        // <B0bar|B0bar(t)>
 
    //
    if ( !mixed && stateAtDeltaTeq0 == B0 ) {
        osc_amp = BB * m_A_f + barBB * m_Abar_f;
    }
    if ( !mixed && stateAtDeltaTeq0 == B0B ) {
        osc_amp = barBbarB * m_Abar_fbar + BbarB * m_A_fbar;
    }
 
    if ( mixed && stateAtDeltaTeq0 == B0 ) {
        osc_amp = barBB * m_Abar_fbar + BB * m_A_fbar;
    }
    if ( mixed && stateAtDeltaTeq0 == B0B ) {
        osc_amp = BbarB * m_A_f + barBbarB * m_Abar_f;
    }
 
    // store the amplitudes for each parent spin basis state
    double norm = 1.0 / p1.d3mag();
    vertex( 0, norm * osc_amp * p1 * ( p->eps( 0 ) ) );
    vertex( 1, norm * osc_amp * p1 * ( p->eps( 1 ) ) );
    vertex( 2, norm * osc_amp * p1 * ( p->eps( 2 ) ) );
 
    return;
}
 
std::string EvtVSSBMixCPT::getParamName( int i )
{
    switch ( i ) {
        case 0:
            return "deltaM";
        case 1:
            return "deltaGammaOverGamma";
        case 2:
            return "qOverP";
        case 3:
            return "qOverPPhase";
        case 4:
            return "Af";
        case 5:
            return "AfPhase";
        case 6:
            return "Abarf";
        case 7:
            return "AbarfPhase";
        case 8:
            return "Afbar";
        case 9:
            return "AfbarPhase";
        case 10:
            return "Abarfbar";
        case 11:
            return "AbarfbarPhase";
        case 12:
            return "Z";
        case 13:
            return "ZPhase";
        default:
            return "";
    }
}
 
std::string EvtVSSBMixCPT::getParamDefault( int i )
{
    switch ( i ) {
        case 3:
            return "0.0";
        case 4:
            return "1.0";
        case 5:
            return "0.0";
        case 6:
            return "1.0";
        case 7:
            return "0.0";
        default:
            return "";
    }
}