STEER/AliKFVertex.cxx

   1 //----------------------------------------------------------------------------
   2 // Implementation of the AliKFVertex class
   3 // .
   4 // @author  S.Gorbunov, I.Kisel
   5 // @version 1.0
   6 // @since   13.05.07
   7 //
   8 // Class to reconstruct and store primary and secondary vertices
   9 // The method is described in CBM-SOFT note 2007-003,
  10 // ``Reconstruction of decayed particles based on the Kalman filter'',
  11 // http://www.gsi.de/documents/DOC-2007-May-14-1.pdf
  12 //
  13 // This class is ALICE interface to general mathematics in AliKFParticleCore
  14 //
  15 //  -= Copyright &copy ALICE HLT Group =-
  16 //____________________________________________________________________________
  17
  18
  19 #include "AliKFVertex.h"
  20 #include "Riostream.h"
  21
  22 ClassImp(AliKFVertex)
  23
  24
  25 AliKFVertex::AliKFVertex( const AliVVertex &vertex ): fIsConstrained(0)
  26 {
  27   // Constructor from ALICE VVertex
  28
  29   vertex.GetXYZ( fP );
  30   vertex.GetCovarianceMatrix( fC );
  31   fChi2 = vertex.GetChi2();
  32   fNDF = 2*vertex.GetNContributors() - 3;
  33   fQ = 0;
  34   fAtProductionVertex = 0;
  35   fIsLinearized = 0;
  36   fSFromDecay = 0;
  37 }
  38
  39 /*
  40 void     AliKFVertex::Print(Option_t* ) const
  41 {
  42   cout<<"AliKFVertex position:    "<<GetX()<<" "<<GetY()<<" "<<GetZ()<<endl;
  43   cout<<"AliKFVertex cov. matrix: "<<GetCovariance(0)<<endl;
  44   cout<<"                         "<<GetCovariance(1)<<" "<<GetCovariance(2)<<endl;
  45   cout<<"                         "<<GetCovariance(3)<<" "<<GetCovariance(4)<<" "<<GetCovariance(5)<<endl;
  46 }
  47   */
  48
  49 void AliKFVertex::SetBeamConstraint( Double_t x, Double_t y, Double_t z,
  50                                       Double_t errX, Double_t errY, Double_t errZ )
  51 {
  52   // Set beam constraint to the vertex
  53   fP[0] = x;
  54   fP[1] = y;
  55   fP[2] = z;
  56   fC[0] = errX*errX;
  57   fC[1] = 0;
  58   fC[2] = errY*errY;
  59   fC[3] = 0;
  60   fC[4] = 0;
  61   fC[5] = errZ*errZ;
  62   fIsConstrained = 1;
  63 }
  64
  65 void AliKFVertex::SetBeamConstraintOff()
  66 {
  67   fIsConstrained = 0;
  68 }
  69
  70 void AliKFVertex::ConstructPrimaryVertex( const AliKFParticle *vDaughters[],
  71                                           int NDaughters, Bool_t vtxFlag[],
  72                                           Double_t ChiCut  )
  73 {
  74   //* Primary vertex finder with simple rejection of outliers
  75   if( NDaughters<2 ) return;
  76   Construct( vDaughters, NDaughters, 0, -1, fIsConstrained );
  77   for( int i=0; i<NDaughters; i++ ) vtxFlag[i] = 1;
  78
  79   Int_t nRest = NDaughters;
  80   while( nRest>2 )
  81     {
  82       Double_t worstChi = 0.;
  83       Int_t worstDaughter = 0;
  84       for( Int_t it=0; it<NDaughters; it++ ){
  85         if( !vtxFlag[it] ) continue;
  86         const AliKFParticle &p = *(vDaughters[it]);
  87         AliKFVertex tmp = *this - p;
  88         Double_t chi = p.GetDeviationFromVertex( tmp );
  89         if( worstChi < chi ){
  90           worstChi = chi;
  91           worstDaughter = it;
  92         }
  93       }
  94       if( worstChi < ChiCut ) break;
  95
  96       vtxFlag[worstDaughter] = 0;
  97       *this -= *(vDaughters[worstDaughter]);
  98       nRest--;
  99     }
 100
 101   if( nRest<=2 && GetChi2()>ChiCut*ChiCut*GetNDF() ){
 102     for( int i=0; i<NDaughters; i++ ) vtxFlag[i] = 0;
 103     fNDF = -3;
 104     fChi2 = 0;
 105   }
 106 }