EvtSVVNONCPEIGEN.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      Royal Holloway, University of London
//
// Module: EvtSVVNONCPEIGEN.cc
//
// Description: Routine to decay scalar -> vector vector
//              and has CP violation.
//
//              This model does all the ckm-suppressed decays and mixing for you. It randomly
//              'overwrites' any reco or tagging state as set in the Y(4S) decay model
//              (VSS_(B)MIX) with its own generated states.
//
//              As such, the corresponding dec file requires only one decay-mode description,
//              for example: Decay MyB0 1.000    rho+ MyD*-       SVV_NONCPEIGEN dm beta gamma
//              0.322 0.31 0.941 0 0.107 1.42 0.02 0 0.02 0 0.02 0 ; EndDecay and furthermore
//              Y(4S) only needs to decay to B0's (or B0bar's). The decay above should be a
//              CKM-favored mode (eg. B0->D*-rho+ or B0bar->D*+rho-). All ckm-suppressed decays
//              and the mixing are derived from this line in the ::Decay function.
//
//              There are 15 or 27 arguments. The first three are dm, phase1
//              and phase2. dm is the B0-B0bar mass difference. Phases 1
//              and 2 are the CKM weak phases relevant for the particular mode,
//              eg for B-->DstRho phase1 is beta and phase2 is gamma.
//
//              The next arguments are the 2 amplitudes (= 12 input parameters)
//              in the order: A_f, Abar_f. In the example above, the 'A_f' amplitude now
//              stands for the ckm-favored decay 'B0->D*-rho+', and 'Abar_f' stands for
//              'B0bar->D*-rho+'
//
//              Each amplitude has its 3 helicity states in the order +, 0, -, which are each
//              specified by a magnitude and a strong phase.
//
//              The last 2 arguments A_fbar and Abar_fbar (=12 input parameters) are not
//              necessary, but can included if one wants to set them differently from A_f,
//              Abar_f.
//
//              Mind you that Hbar_+- = H_-+ (ignoring the weak phase, which flips sign).
//              It is custumary to select one set of helicity states (eg H_+-) and to adopt
//              these for the CP-conjugate decays as well (ie. depict Hbar_-+ with H_+-), which
//              is the interpretation we use for the input-parameters above. However, the
//              angular decay in EvtGen is just a formula in which helicity amplitudes are
//              'plugged' in, making no difference between B0 or B0bar decays. In the model
//              below we (thus) account for the +- flipping between B0 and B0bar.
//
//
// Modification history:
//    Ajit Kurup 9 March 2001        Module created (from EvtSVSNONCPEIGEN)
//    Max Baak 01/16/2004            Fix of Helicity amplitude ordering.
//                                   Decay also works for B0bar decays.
//------------------------------------------------------------------------
//
#include "EvtSVVNONCPEIGEN.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/EvtVector4C.hh"
#include "EvtSVVHelAmp.hh"
#include <stdlib.h>
#include <string>
 
EvtSVVNONCPEIGEN::~EvtSVVNONCPEIGEN() {}
 
void EvtSVVNONCPEIGEN::getName( std::string& model_name ) { model_name = "SVV_NONCPEIGEN"; }
 
EvtDecayBase* EvtSVVNONCPEIGEN::clone() { return new EvtSVVNONCPEIGEN; }
 
void EvtSVVNONCPEIGEN::init() {
 
  // check that there are 27 arguments
  checkNArg( 27, 15 );
  checkNDaug( 2 );
 
  checkSpinDaughter( 0, EvtSpinType::VECTOR );
  checkSpinDaughter( 1, EvtSpinType::VECTOR );
 
  //  The ordering of A_f is :
  //  A_f[0-2] = A_f
  //  A_f[3-5] = Abar_f
  //  A_f[6-8] = A_fbar
  //  A_f[9-11] = Abar_fbar
  //
  //  Each of the 4 amplitudes include the 3 different helicity states in
  //  the order +, 0, -. See more about helicity amplitude ordering in ::decay
 
  int i = 0;
  int j = ( getNArg() - 3 ) / 2;
 
  for ( i = 0; i < j; ++i )
  {
    _A_f[i] = getArg( ( 2 * i ) + 3 ) *
              EvtComplex( cos( getArg( ( 2 * i ) + 4 ) ), sin( getArg( ( 2 * i ) + 4 ) ) );
  }
 
  //  If only 6 amplitudes are specified, calculate the last 6 from the first 6:
  if ( 6 == j )
  {
    for ( i = 0; i < 3; ++i )
    {
      _A_f[6 + i] = _A_f[3 + i];
      _A_f[9 + i] = _A_f[i];
    }
  }
}
 
void EvtSVVNONCPEIGEN::initProbMax() {
  double probMax = 0;
  for ( int i = 0; i < 12; ++i )
  {
    double amp = abs( _A_f[i] );
    probMax += amp * amp;
  }
 
  setProbMax( probMax );
}
 
void EvtSVVNONCPEIGEN::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;
  EvtId  daugs[2];
 
  // MB: flip selects the final of the decay
  int flip = ( ( p->getId() == B0 ) ? 0 : 1 );
  daugs[0] = getDaug( 0 );
  daugs[1] = getDaug( 1 );
  p->initializePhaseSpace( 2, daugs );
 
  EvtCPUtil::OtherB( p, t, other_b, 0.5 );
 
  EvtComplex amp[3];
 
  double     dmt2   = getArg( 0 ) * t / ( 2 * EvtConst::c );
  double     phiCKM = ( 2.0 * getArg( 1 ) + getArg( 2 ) ); // 2b+g
  EvtComplex ePlusIPhi( cos( phiCKM ), sin( phiCKM ) );
  EvtComplex eMinusIPhi( cos( -phiCKM ), sin( -phiCKM ) );
 
  // flip == 0 : D*-rho+
  // flip == 1 : D*+rho-
 
  if ( !flip )
  {
    if ( other_b == B0B )
    {
      // At t=0 we have a B0
      for ( int i = 0; i < 3; ++i )
      {
        amp[i] =
            _A_f[i] * cos( dmt2 ) + eMinusIPhi * EvtComplex( 0.0, sin( dmt2 ) ) * _A_f[i + 3];
      }
    }
    if ( other_b == B0 )
    {
      // At t=0 we have a B0bar
      for ( int i = 0; i < 3; ++i )
      {
        amp[i] =
            _A_f[i] * ePlusIPhi * EvtComplex( 0.0, sin( dmt2 ) ) + _A_f[i + 3] * cos( dmt2 );
      }
    }
  }
  else
  {
    if ( other_b == B0B )
    {
      // At t=0 we have a B0
 
      // M.Baak 01/16/2004
      // Note: \bar{H}+- = H-+
      // If one wants to use the correct helicities for B0 and B0bar decays but the same
      // formula-notation (as done in EvtSVV_HelAmp), count the B0bar helicities backwards.
      // (Equivalently, one could flip the chi angle.)
 
      for ( int i = 0; i < 3; ++i )
      {
        amp[i] = _A_f[8 - i] * cos( dmt2 ) +
                 eMinusIPhi * EvtComplex( 0.0, sin( dmt2 ) ) * _A_f[11 - i];
      }
    }
    if ( other_b == B0 )
    {
      // At t=0 we have a B0bar
      for ( int i = 0; i < 3; ++i )
      {
        amp[i] = _A_f[8 - i] * ePlusIPhi * EvtComplex( 0.0, sin( dmt2 ) ) +
                 _A_f[11 - i] * cos( dmt2 );
      }
    }
  }
 
  EvtSVVHelAmp::SVVHel( p, _amp2, daugs[0], daugs[1], amp[0], amp[1], amp[2] );
 
  return;
}