EvtSSDCP.cc

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//--------------------------------------------------------------------------
//
// Environment:
//      This software is part of the EvtGen package developed jointly
//      for the BaBar and CLEO collaborations.  If you use all or part
//      of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/COPYRIGHT
//      Copyright (C) 2001      Caltech
//
// Module: EvtSSDCP.cc
//
// Description: See EvtSSDCP.hh
//
// Modification history:
//
//    RYD       August 12, 2001        Module created
//    F. Sandrelli, Fernando M-V  March 1, 2002     Debugged and added z parameter (CPT
//    violation)
//------------------------------------------------------------------------
//
#include "EvtSSDCP.hh"
#include "../EvtGenBase/EvtCPUtil.hh"
#include "../EvtGenBase/EvtConst.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtRandom.hh"
#include "../EvtGenBase/EvtReport.hh"
#include "../EvtGenBase/EvtTensor4C.hh"
#include "../EvtGenBase/EvtVector4C.hh"
#include <stdlib.h>
#include <string>
using std::endl;
 
EvtSSDCP::~EvtSSDCP() {}
 
void EvtSSDCP::getName( std::string& model_name ) { model_name = "SSD_CP"; }
 
EvtDecayBase* EvtSSDCP::clone() { return new EvtSSDCP; }
 
void EvtSSDCP::init() {
 
  // check that there are 8 or 12 or 14 arguments
 
  checkNArg( 14, 12, 8 );
  checkNDaug( 2 );
 
  EvtSpinType::spintype d1type = EvtPDL::getSpinType( getDaug( 0 ) );
  EvtSpinType::spintype d2type = EvtPDL::getSpinType( getDaug( 1 ) );
 
  // FS commented this check to include alias of B0
  //  if ( !((getParentId() == EvtPDL::getId("B0"))||(getParentId() == EvtPDL::getId("B0B"))) )
  //  {
  //    report(ERROR, "EvtGen") << "EvtSSDCP cannot decay "
  //            << EvtPDL::name(getParentId())
  //            << ". Must be specified to decay"
  //            << " only B0 or a B0B ." << endl;
  //  report(ERROR,"EvtGen") << "Will terminate execution!"<<endl;
  //  ::abort();
  //}
 
  if ( ( !( d1type == EvtSpinType::SCALAR || d2type == EvtSpinType::SCALAR ) ) ||
       ( !( ( d2type == EvtSpinType::SCALAR ) || ( d2type == EvtSpinType::VECTOR ) ||
            ( d2type == EvtSpinType::TENSOR ) ) ) ||
       ( !( ( d1type == EvtSpinType::SCALAR ) || ( d1type == EvtSpinType::VECTOR ) ||
            ( d1type == EvtSpinType::TENSOR ) ) ) )
  {
    report( ERROR, "EvtGen" ) << "EvtSSDCP generator expected "
                              << "one of the daugters to be a scalar, the other either "
                                 "scalar, vector, or tensor, found:"
                              << EvtPDL::name( getDaug( 0 ) ).c_str() << " and "
                              << EvtPDL::name( getDaug( 1 ) ).c_str() << endl;
    report( ERROR, "EvtGen" ) << "Will terminate execution!" << endl;
    ::abort();
  }
 
  _dm = getArg( 0 ) / EvtConst::c; // units of 1/mm
 
  _dgog = getArg( 1 );
 
  _qoverp = getArg( 2 ) * EvtComplex( cos( getArg( 3 ) ), sin( getArg( 3 ) ) );
  _poverq = 1.0 / _qoverp;
 
  _A_f = getArg( 4 ) * EvtComplex( cos( getArg( 5 ) ), sin( getArg( 5 ) ) );
 
  _Abar_f = getArg( 6 ) * EvtComplex( cos( getArg( 7 ) ), sin( getArg( 7 ) ) );
 
  if ( getNArg() >= 12 )
  {
    _eigenstate = false;
    _A_fbar     = getArg( 8 ) * EvtComplex( cos( getArg( 9 ) ), sin( getArg( 9 ) ) );
    _Abar_fbar  = getArg( 10 ) * EvtComplex( cos( getArg( 11 ) ), sin( getArg( 11 ) ) );
  }
  else
  {
    // I'm somewhat confused about this. For a CP eigenstate set the
    // amplitudes to the same. For a non CP eigenstate CPT invariance
    // is enforced. (ryd)
    if ( ( getDaug( 0 ) == EvtPDL::chargeConj( getDaug( 0 ) ) &&
           getDaug( 1 ) == EvtPDL::chargeConj( getDaug( 1 ) ) ) ||
         ( getDaug( 0 ) == EvtPDL::chargeConj( getDaug( 1 ) ) &&
           getDaug( 1 ) == EvtPDL::chargeConj( getDaug( 0 ) ) ) )
    { _eigenstate = true; }
    else
    {
      _eigenstate = false;
      _A_fbar     = conj( _Abar_f );
      _Abar_fbar  = conj( _A_f );
    }
  }
 
  // FS: new check for z
  if ( getNArg() == 14 )
  { // FS Set _z parameter if provided else set it 0
    _z = EvtComplex( getArg( 12 ), getArg( 13 ) );
  }
  else { _z = EvtComplex( 0.0, 0.0 ); }
 
  // FS substituted next 2 lines...
 
  //
  //  _gamma=EvtPDL::getctau(EvtPDL::getId("B0"));  //units of 1/mm
  //_dgamma=_gamma*0.5*_dgog;
  //
  // ...with:
 
  _gamma  = 1 / EvtPDL::getctau( EvtPDL::getId( "B0" ) ); // gamma/c (1/mm)
  _dgamma = _gamma * _dgog;                               // dgamma/c (1/mm)
 
  if ( verbose() )
  {
    report( INFO, "EvtGen" ) << "SSD_CP will generate CP/CPT violation:" << 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
                             << "dGamma      = " << _dgamma << " ps-1" << endl
                             << "       q/p  = " << _qoverp << endl
                             << "        z  = " << _z << endl
                             << "       tau  = " << 1. / _gamma << " ps" << endl;
  }
}
 
void EvtSSDCP::initProbMax() {
  double theProbMax = abs( _A_f ) * abs( _A_f ) + abs( _Abar_f ) * abs( _Abar_f ) +
                      abs( _A_fbar ) * abs( _A_fbar ) + abs( _Abar_fbar ) * abs( _Abar_fbar );
 
  if ( _eigenstate ) theProbMax *= 2;
 
  EvtSpinType::spintype d2type = EvtPDL::getSpinType( getDaug( 1 ) );
  EvtSpinType::spintype d1type = EvtPDL::getSpinType( getDaug( 0 ) );
  if ( d1type == EvtSpinType::TENSOR || d2type == EvtSpinType::TENSOR ) theProbMax *= 10;
 
  setProbMax( theProbMax );
}
 
void EvtSSDCP::decay( EvtParticle* p ) {
 
  static EvtId B0  = EvtPDL::getId( "B0" );
  static EvtId B0B = EvtPDL::getId( "anti-B0" );
 
  double t;
  EvtId  other_b;
  EvtId  daugs[2];
 
  int flip = 0;
  if ( !_eigenstate )
  {
    if ( EvtRandom::Flat( 0.0, 1.0 ) < 0.5 ) flip = 1;
  }
 
  if ( !flip )
  {
    daugs[0] = getDaug( 0 );
    daugs[1] = getDaug( 1 );
  }
  else
  {
    daugs[0] = EvtPDL::chargeConj( getDaug( 0 ) );
    daugs[1] = EvtPDL::chargeConj( getDaug( 1 ) );
  }
 
  EvtParticle* d;
  p->initializePhaseSpace( 2, daugs );
 
  EvtComplex amp;
 
  EvtCPUtil::OtherB( p, t, other_b, 0.5 ); // t is c*Dt (mm)
 
  // if (flip) t=-t;
 
  // FS We assume DGamma=GammaLow-GammaHeavy and Dm=mHeavy-mLow
  EvtComplex expL = exp( -EvtComplex( -0.25 * _dgamma * t, 0.5 * _dm * t ) );
  EvtComplex expH = exp( EvtComplex( -0.25 * _dgamma * t, 0.5 * _dm * t ) );
  // FS Definition of gp and gm
  EvtComplex gp = 0.5 * ( expL + expH );
  EvtComplex gm = 0.5 * ( expL - expH );
  // FS Calculation os sqrt(1-z^2)
  EvtComplex sqz = sqrt( abs( 1 - _z * _z ) ) * exp( EvtComplex( 0, arg( 1 - _z * _z ) / 2 ) );
 
  // EvtComplex BB=0.5*(expL+expH);                  // <B0|B0(t)>
  // EvtComplex barBB=_qoverp*0.5*(expL-expH);       // <B0bar|B0(t)>
  // EvtComplex BbarB=_poverq*0.5*(expL-expH);       // <B0|B0bar(t)>
  // EvtComplex barBbarB=BB;                         // <B0bar|B0bar(t)>
  //   FS redefinition of these guys... (See BAD #188 eq.35 for ref.)
  //   q/p is taken as in the BaBar Phys. Book (opposite sign wrt ref.)
  EvtComplex BB       = gp + _z * gm;       // <B0|B0(t)>
  EvtComplex barBB    = sqz * _qoverp * gm; // <B0bar|B0(t)>
  EvtComplex BbarB    = sqz * _poverq * gm; // <B0|B0bar(t)>
  EvtComplex barBbarB = gp - _z * gm;       // <B0bar|B0bar(t)>
 
  if ( !flip )
  {
    if ( other_b == B0B )
    {
      // at t=0 we have a B0
      // report(INFO,"EvtGen") << "B0B"<<endl;
      amp = BB * _A_f + BbarB * _Abar_f;
      // std::cout << "noflip B0B tag:"<<amp<<std::endl;
      // amp=0.0;
    }
    if ( other_b == B0 )
    {
      // report(INFO,"EvtGen") << "B0"<<endl;
      amp = barBB * _A_f + barBbarB * _Abar_f;
    }
  }
  else
  {
    if ( other_b == B0 )
    {
      amp = barBB * _A_fbar + barBbarB * _Abar_fbar;
      // std::cout << "flip B0 tag:"<<amp<<std::endl;
      // amp=0.0;
    }
    if ( other_b == B0B ) { amp = BB * _A_fbar + BbarB * _Abar_fbar; }
  }
 
  EvtVector4R p4_parent = p->getP4Restframe();
  double      m_parent  = p4_parent.mass();
 
  EvtSpinType::spintype d2type = EvtPDL::getSpinType( getDaug( 1 ) );
 
  EvtVector4R momv;
  EvtVector4R moms;
 
  if ( d2type == EvtSpinType::SCALAR )
  {
    d2type = EvtPDL::getSpinType( getDaug( 0 ) );
    d      = p->getDaug( 0 );
    momv   = d->getP4();
    moms   = p->getDaug( 1 )->getP4();
  }
  else
  {
    d    = p->getDaug( 1 );
    momv = d->getP4();
    moms = p->getDaug( 0 )->getP4();
  }
 
  if ( d2type == EvtSpinType::SCALAR ) { vertex( amp ); }
 
  if ( d2type == EvtSpinType::VECTOR )
  {
 
    double norm = momv.mass() / ( momv.d3mag() * p->mass() );
 
    vertex( 0, amp * norm * p4_parent * ( d->epsParent( 0 ) ) );
    vertex( 1, amp * norm * p4_parent * ( d->epsParent( 1 ) ) );
    vertex( 2, amp * norm * p4_parent * ( d->epsParent( 2 ) ) );
  }
 
  if ( d2type == EvtSpinType::TENSOR )
  {
 
    double norm =
        d->mass() * d->mass() / ( m_parent * d->getP4().d3mag() * d->getP4().d3mag() );
 
    vertex( 0, amp * norm * d->epsTensorParent( 0 ).cont1( p4_parent ) * p4_parent );
    vertex( 1, amp * norm * d->epsTensorParent( 1 ).cont1( p4_parent ) * p4_parent );
    vertex( 2, amp * norm * d->epsTensorParent( 2 ).cont1( p4_parent ) * p4_parent );
    vertex( 3, amp * norm * d->epsTensorParent( 3 ).cont1( p4_parent ) * p4_parent );
    vertex( 4, amp * norm * d->epsTensorParent( 4 ).cont1( p4_parent ) * p4_parent );
  }
 
  return;
}