EvtSSSCPpng.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) 1998      Caltech, UCSB
//
// Module: EvtSSSCPpng.cc
//
// Description: Routine to decay B -> 2 scalars taking into account penguin
//              contributions (assuming single quark dominance for penguins)
//
// Modification history:
//
//    RYD/NK    December 3, 1997          Module created
//
//------------------------------------------------------------------------
//
#include "EvtSSSCPpng.hh"
#include "../EvtGenBase/EvtCPUtil.hh"
#include "../EvtGenBase/EvtConst.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtId.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtRandom.hh"
#include "../EvtGenBase/EvtReport.hh"
#include <stdlib.h>
#include <string>
 
EvtSSSCPpng::~EvtSSSCPpng() {}
 
void EvtSSSCPpng::getName( std::string& model_name ) { model_name = "SSS_CP_PNG"; }
 
EvtDecayBase* EvtSSSCPpng::clone() { return new EvtSSSCPpng; }
 
void EvtSSSCPpng::init() {
 
  // check that there are 7 arguments
  checkNArg( 7 );
  checkNDaug( 2 );
 
  checkSpinParent( EvtSpinType::SCALAR );
 
  checkSpinDaughter( 0, EvtSpinType::SCALAR );
  checkSpinDaughter( 1, EvtSpinType::SCALAR );
}
 
void EvtSSSCPpng::initProbMax() {
 
  setProbMax( getArg( 5 ) * getArg( 5 ) * ( 1 + getArg( 6 ) * getArg( 6 ) ) );
}
 
void EvtSSSCPpng::decay( EvtParticle* p ) {
 
  // added by Lange Jan4,2000
  static EvtId B0  = EvtPDL::getId( "B0" );
  static EvtId B0B = EvtPDL::getId( "anti-B0" );
 
  double t;
  EvtId  other_b;
 
  p->initializePhaseSpace( getNDaug(), getDaugs() );
 
  EvtComplex amp;
 
  EvtComplex A, Abar;
  // EvtComplex ACC, AbarCC;
 
  // assume single (top) quark dominance for the penguin.
 
  // old: a0=alpha, a1=dm, a2=1, a3=1, a4=0, a5=1, a6=0
  // new: a0=beta, a1=gamma, a2=delta, a3=dm, a4=1, a5=1=A_{T}, a6=A_{P}/A_{T}
 
  // e.g., for B -> pi pi
  // A_{T} = |V_{ub} V_{ud}| T
  // A_{P} = |V_{tb} V_{td}| P
  // P and T are purely hadronic matrix elements
  // P/T = 0.055, A_{P}/A_{T} = 0.2 (see Marrocchesi and Paver, hep-ph/9702353)
 
  // A = A_{T}( exp(i(beta+gamma)) + (A_{P}/A_{T}) exp(i(delta))
  // A_bar = same, except for the sign of the weak phases
  // here, delta = delta_{p}-delta_{t} (rel. strong phase)
 
  A = getArg( 5 ) *
      ( EvtComplex( cos( -getArg( 0 ) - getArg( 1 ) ), sin( -getArg( 0 ) - getArg( 1 ) ) ) +
        getArg( 6 ) * EvtComplex( cos( getArg( 2 ) ), sin( getArg( 2 ) ) ) );
 
  Abar = getArg( 5 ) *
         ( EvtComplex( cos( getArg( 0 ) + getArg( 1 ) ), sin( getArg( 0 ) + getArg( 1 ) ) ) +
           getArg( 6 ) * EvtComplex( cos( getArg( 2 ) ), sin( getArg( 2 ) ) ) );
 
  // get fraction of B0 tags with these amplitudes
 
  // double xd = 0.65;
  double ratio = 1 / ( 1 + 0.65 * 0.65 );
 
  EvtComplex rf, rbarf;
 
  rf    = EvtComplex( cos( 2.0 * getArg( 0 ) ), sin( 2.0 * getArg( 0 ) ) ) * Abar / A;
  rbarf = EvtComplex( 1.0 ) / rf;
 
  double A2    = real( A ) * real( A ) + imag( A ) * imag( A );
  double Abar2 = real( Abar ) * real( Abar ) + imag( Abar ) * imag( Abar );
 
  double rf2    = real( rf ) * real( rf ) + imag( rf ) * imag( rf );
  double rbarf2 = real( rbarf ) * real( rbarf ) + imag( rbarf ) * imag( rbarf );
 
  // fraction of B0 _tags_
  double fract = ( Abar2 * ( 1 + rbarf2 + ( 1 - rbarf2 ) * ratio ) ) /
                 ( Abar2 * ( 1 + rbarf2 + ( 1 - rbarf2 ) * ratio ) +
                   A2 * ( 1 + rf2 + ( 1 - rf2 ) * ratio ) );
 
  EvtCPUtil::OtherB( p, t, other_b, fract );
 
  // this method works just as well -- NK
  // randomly generate the tag (B0 or B0B)
 
  //  double tag = EvtRandom::Flat(0.0,1.0);
  //  if (tag < 0.5) {
  //
  //   EvtCPUtil::OtherB(p,t,other_b,1.0);
  //   other_b = B0;
  //  }
  //  else {
  //
  //   EvtCPUtil::OtherB(p,t,other_b,0.0);
  //   other_b = B0B;
  //  }
 
  // mixing angle = -beta
 
  if ( other_b == B0B )
  {
    amp = A * cos( getArg( 3 ) * t / ( 2 * EvtConst::c ) ) +
          EvtComplex( cos( 2.0 * getArg( 0 ) ), sin( 2.0 * getArg( 0 ) ) ) * getArg( 4 ) *
              EvtComplex( 0.0, 1.0 ) * Abar * sin( getArg( 3 ) * t / ( 2 * EvtConst::c ) );
  }
  if ( other_b == B0 )
  {
    amp = A * EvtComplex( cos( -2.0 * getArg( 0 ) ), sin( -2.0 * getArg( 0 ) ) ) *
              EvtComplex( 0.0, 1.0 ) * sin( getArg( 3 ) * t / ( 2 * EvtConst::c ) ) +
          getArg( 4 ) * Abar * cos( getArg( 3 ) * t / ( 2 * EvtConst::c ) );
  }
 
  vertex( amp );
 
  return;
}