A new function for propagating the tracks taking into account all three components...

diff --git a/STEER/AliTracker.cxx b/STEER/AliTracker.cxx
index c755dc82f31cb368641d6c570e3cdd08989e9d68..37b65e6d7496b63b4d20682f8b29eaa308d65d1c 100644 (file)
--- a/STEER/AliTracker.cxx
+++ b/STEER/AliTracker.cxx
@@ -94,6 +94,28 @@ Double_t AliTracker::GetBz(const Double_t *r) {
   return  TMath::Sign(0.5*kAlmost0Field,bz) + bz;
 }
 
+//__________________________________________________________________________
+void AliTracker::GetBxByBz(const Double_t r[3], Double_t b[3]) {
+  //------------------------------------------------------------------
+  // Returns Bx, By and Bz (kG) at the point "r" .
+  //------------------------------------------------------------------
+  AliMagF* fld = (AliMagF*)TGeoGlobalMagField::Instance()->GetField();
+  if (!fld) {
+     b[0] = b[1] = 0.;
+     b[2] = 0.5*kAlmost0Field;
+     return;
+  }
+
+  if (fld->IsUniform()) {
+     b[0] = b[1] = 0.;
+     b[2] = fld->SolenoidField();
+  }  else {
+     fld->Field(r,b);
+  }
+  b[2] = (TMath::Sign(0.5*kAlmost0Field,b[2]) + b[2]);
+  return;
+}
+
 //__________________________________________________________________________
 void AliTracker::FillClusterArray(TObjArray* /*array*/) const
 {
@@ -372,6 +394,61 @@ Double_t mass, Double_t maxStep, Bool_t rotateTo, Double_t maxSnp){
   return kTRUE;
 }
 
+Bool_t 
+AliTracker::PropagateTrackToBxByBz(AliExternalTrackParam *track,
+Double_t xToGo, 
+Double_t mass, Double_t maxStep, Bool_t rotateTo, Double_t maxSnp){
+  //----------------------------------------------------------------
+  //
+  // Propagates the track to the plane X=xk (cm)
+  // taking into account all the three components of the magnetic field 
+  // and correcting for the crossed material.
+  //
+  // mass     - mass used in propagation - used for energy loss correction
+  // maxStep  - maximal step for propagation
+  //
+  //  Origin: Marian Ivanov,  Marian.Ivanov@cern.ch
+  //
+  //----------------------------------------------------------------
+  const Double_t kEpsilon = 0.00001;
+  Double_t xpos     = track->GetX();
+  Double_t dir      = (xpos<xToGo) ? 1.:-1.;
+  //
+  while ( (xToGo-xpos)*dir > kEpsilon){
+    Double_t step = dir*TMath::Min(TMath::Abs(xToGo-xpos), maxStep);
+    Double_t x    = xpos+step;
+    Double_t xyz0[3],xyz1[3],param[7];
+    track->GetXYZ(xyz0);   //starting global position
+
+    Double_t b[3]; GetBxByBz(xyz0,b); // getting the local Bx, By and Bz
+
+    if (!track->GetXYZAt(x,b[2],xyz1)) return kFALSE;   // no prolongation
+    xyz1[2]+=kEpsilon; // waiting for bug correction in geo
+
+    if (TMath::Abs(track->GetSnpAt(x,b[2])) >= maxSnp) return kFALSE;
+    if (!track->PropagateToBxByBz(x,b))  return kFALSE;
+
+    MeanMaterialBudget(xyz0,xyz1,param);       
+    Double_t xrho=param[0]*param[4], xx0=param[1];
+
+    if (!track->CorrectForMeanMaterial(xx0,xrho,mass)) return kFALSE;
+    if (rotateTo){
+      if (TMath::Abs(track->GetSnp()) >= maxSnp) return kFALSE;
+      track->GetXYZ(xyz0);   // global position
+      Double_t alphan = TMath::ATan2(xyz0[1], xyz0[0]); 
+      //
+      Double_t ca=TMath::Cos(alphan-track->GetAlpha()), 
+               sa=TMath::Sin(alphan-track->GetAlpha());
+      Double_t sf=track->GetSnp(), cf=TMath::Sqrt((1.-sf)*(1.+sf));
+      Double_t sinNew =  sf*ca - cf*sa;
+      if (TMath::Abs(sinNew) >= maxSnp) return kFALSE;
+      if (!track->Rotate(alphan)) return kFALSE;
+    }
+    xpos = track->GetX();
+  }
+  return kTRUE;
+}
+
 void AliTracker::FillResiduals(const AliExternalTrackParam *t,
                              Double_t *p, Double_t *cov, 
                               UShort_t id, Bool_t updated) {

diff --git a/STEER/AliTracker.h b/STEER/AliTracker.h
index e3b1ea3e200fd51700bb0631c1572522592dc240..a9127285f999aed4e57c31bd768d7a7fdcc4f56f 100644 (file)
--- a/STEER/AliTracker.h
+++ b/STEER/AliTracker.h
@@ -61,8 +61,12 @@ public:
   static
   Bool_t PropagateTrackTo(AliExternalTrackParam *track, Double_t x, Double_t m,
         Double_t maxStep, Bool_t rotateTo=kTRUE, Double_t maxSnp=0.8);  
+  Bool_t PropagateTrackToBxByBz(AliExternalTrackParam *track, Double_t x, 
+         Double_t m,
+        Double_t maxStep, Bool_t rotateTo=kTRUE, Double_t maxSnp=0.8);  
   //
   static Double_t GetBz(const Double_t *r);
+  static void GetBxByBz(const Double_t r[3], Double_t b[3]);
   static Double_t GetBz();
   static Bool_t   UniformField();
   //