AliDecayer realisation for the EvtGen code and EvtGen itself.

[u/mrichter/AliRoot.git] / TEvtGen / EvtGenModels / EvtLambdaP_BarGamma.cxx

diff --git a/TEvtGen/EvtGenModels/EvtLambdaP_BarGamma.cxx b/TEvtGen/EvtGenModels/EvtLambdaP_BarGamma.cxx
new file mode 100644 (file)
index 0000000..d9db16b
--- /dev/null
+++ b/TEvtGen/EvtGenModels/EvtLambdaP_BarGamma.cxx
@@ -0,0 +1,136 @@
+//--------------------------------------------------------------------------
+//
+// 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) 2003      Caltech
+//
+// Module: EvtGen/EvtRadiativeBaryonicPenguins.hh
+//
+// Description:Implementation of the decay B- -> lambda p_bar gamma according to
+// Cheng, Yang; hep-ph/0201015
+//
+// Modification history:
+//
+//    JFS     December 16th, 2003         Module created
+//
+//------------------------------------------------------------------------
+#include "EvtGenBase/EvtPatches.hh"
+
+#include "EvtGenModels/EvtLambdaP_BarGamma.hh"
+#include "EvtGenBase/EvtGammaMatrix.hh"
+#include "EvtGenBase/EvtDiracSpinor.hh"
+#include "EvtGenBase/EvtSpinType.hh"
+#include "EvtGenBase/EvtDiracParticle.hh"
+#include "EvtGenBase/EvtPhotonParticle.hh"
+#include <stdlib.h>
+using std::cout;
+using std::endl;
+
+EvtLambdaP_BarGamma::EvtLambdaP_BarGamma() :
+  _mLambdab   ( 5.624),            // Lambda_b mass
+  _mLambda0    ( 1.115684),         // Lambda0 mass
+  _c7Eff       ( -0.31),            // Wilson coefficient                                      
+  _mb          (  4.4),             // running b mass                                          
+  _mV          (  5.42),            // pole mass vector current                                
+  _mA          (  5.86),            // pole mass axial current                                 
+  _GF          (  1.166E-5),        // Fermi constant                                          
+  _gLambdab   (  16),               // coupling constant Lambda_b -> B- p
+  _e0          (  1),               // electromagnetic coupling (+1)                           
+  _g1          (  0.64),            // heavy-light form factors at q_mSqare                    
+  _g2          ( -0.10),     
+  _f1          (  0.64),
+  _f2          ( -0.31),
+  _VtbVtsStar ( 0.038)            // |V_tb V_ts^*|
+{
+}
+
+
+
+std::string EvtLambdaP_BarGamma::getName(){
+    return "B_TO_LAMBDA_PBAR_GAMMA";
+}
+
+EvtDecayBase* EvtLambdaP_BarGamma::clone(){
+    return new EvtLambdaP_BarGamma;
+}
+
+void EvtLambdaP_BarGamma::init() {
+    // no arguments, daughter lambda p_bar gamma
+    checkNArg(0);
+    checkNDaug(3);
+    
+    checkSpinParent(EvtSpinType::SCALAR);
+    checkSpinDaughter(0, EvtSpinType::DIRAC);
+    checkSpinDaughter(1, EvtSpinType::DIRAC);
+    checkSpinDaughter(2, EvtSpinType::PHOTON);    
+}
+
+
+// initialize phasespace and calculate the amplitude
+void EvtLambdaP_BarGamma::decay(EvtParticle* p) {
+    EvtComplex I(0, 1);
+    
+    p->initializePhaseSpace(getNDaug(), getDaugs());
+    
+    EvtDiracParticle* theLambda = static_cast<EvtDiracParticle*>(p->getDaug(0));
+    EvtVector4R lambdaMomentum = theLambda->getP4Lab();
+    
+    EvtDiracParticle* theAntiP = static_cast<EvtDiracParticle*>(p->getDaug(1));
+    
+    EvtPhotonParticle* thePhoton = static_cast<EvtPhotonParticle*>(p->getDaug(2));
+    EvtVector4R photonMomentum = thePhoton->getP4Lab();     // get momentum in the same frame
+        
+    // loop over all possible spin states
+    for (int i=0; i<2; ++i) {
+      EvtDiracSpinor lambdaPol = theLambda->spParent(i);
+      for (int j=0; j<2; ++j)  {
+       EvtDiracSpinor antiP_Pol = theAntiP->spParent(j);
+       for (int k=0; k<2; ++k) {
+         EvtVector4C photonPol = thePhoton->epsParentPhoton(k); // one of two possible polarization states
+         EvtGammaMatrix photonGamma; // sigma[mu][nu] * epsilon[mu] * k[nu] (watch lower indices)
+         for (int mu=0; mu<4; ++mu)
+           for (int nu=0; nu<4; ++nu)
+             photonGamma += EvtGammaMatrix::sigmaLower(mu, nu) * photonPol.get(mu) * photonMomentum.get(nu);
+         
+         EvtComplex amp = 
+           -I*_gLambdab * lambdaPol.adjoint() * ((constA()*EvtGammaMatrix::id() + constB()*EvtGammaMatrix::g5())
+                                                  * photonGamma * (slash(lambdaMomentum) + slash(photonMomentum) + _mLambdab*EvtGammaMatrix::id())
+                                                  / ((lambdaMomentum + photonMomentum)*(lambdaMomentum + photonMomentum) - _mLambdab*_mLambdab)
+                                                  * EvtGammaMatrix::g5() * antiP_Pol);
+         // use of parentheses so I do not have to define EvtDiracSpinor*EvtGammaMatrix, which shouldn't be defined to prevent errors in indexing
+
+         vertex(i, j, k, amp);
+       }
+      }
+    }
+}
+
+void EvtLambdaP_BarGamma::initProbMax()
+{
+    // setProbMax(1);
+    setProbMax(9.0000E-13); // found by trial and error
+}
+
+// form factors at 0
+const double EvtLambdaP_BarGamma::f0(double fqm, int n){
+    return fqm * pow(1 - pow(_mLambdab - _mLambda0, 2) / (_mV * _mV), n);
+}
+
+const double EvtLambdaP_BarGamma::g0(double gqm, int n){
+    return gqm * pow(1 - pow(_mLambdab - _mLambda0, 2) / (_mA * _mA), n);
+}
+
+
+const double EvtLambdaP_BarGamma::constA(){
+    return _GF/sqrt(2.) * _e0 / (8 * EvtConst::pi*EvtConst::pi) * 2 * _c7Eff * _mb * _VtbVtsStar
+        * (f0(_f1) - f0(_f2));
+}
+
+const double EvtLambdaP_BarGamma::constB(){
+    return _GF/sqrt(2.) * _e0 / (8 * EvtConst::pi*EvtConst::pi) * 2 * _c7Eff * _mb * _VtbVtsStar
+        * (g0(_g1) - (_mLambdab - _mLambda0) / (_mLambdab + _mLambda0) * g0(_g2));
+}