X-Git-Url: http://git.uio.no/git/?a=blobdiff_plain;f=MUON%2FAliMUONTrackExtrap.cxx;h=e136fef62be51699619990f78fccfa123c987e41;hb=3d9a3ee315ea13df2ec213a606f1d060d6818230;hp=42fe6ffb4db9f55e755c34f4e88ae4ce059bafd1;hpb=4284483e6e9366546ff7c5fd437912accdf263f5;p=u%2Fmrichter%2FAliRoot.git

diff --git a/MUON/AliMUONTrackExtrap.cxx b/MUON/AliMUONTrackExtrap.cxx
index 42fe6ffb4db..e136fef62be 100644
--- a/MUON/AliMUONTrackExtrap.cxx
+++ b/MUON/AliMUONTrackExtrap.cxx
@@ -15,39 +15,55 @@
 
 /* $Id$ */
 
-///////////////////////////////////////////////////
-//
-// Tools
-// for
-// track
-// extrapolation
-// in
-// ALICE
-// dimuon
-// spectrometer
-//
-///////////////////////////////////////////////////
-
-#include <Riostream.h>
-#include <TMath.h>
-#include <TMatrixD.h>
+//-----------------------------------------------------------------------------
+// Class AliMUONTrackExtrap
+// ------------------------
+// Tools for track extrapolation in ALICE dimuon spectrometer
+// Author: Philippe Pillot
+//-----------------------------------------------------------------------------
 
 #include "AliMUONTrackExtrap.h" 
 #include "AliMUONTrackParam.h"
 #include "AliMUONConstants.h"
-#include "AliMagF.h" 
-#include "AliLog.h" 
-#include "AliTracker.h"
+#include "AliMUONReconstructor.h"
+
+#include "AliMagF.h"
+#include "AliExternalTrackParam.h"
+
+#include <TGeoGlobalMagField.h>
+#include <TGeoManager.h>
+#include <TMath.h>
+#include <TDatabasePDG.h>
+
+#include <Riostream.h>
 
+/// \cond CLASSIMP
 ClassImp(AliMUONTrackExtrap) // Class implementation in ROOT context
+/// \endcond
 
-const AliMagF* AliMUONTrackExtrap::fgkField = 0x0;
+const Double_t AliMUONTrackExtrap::fgkSimpleBPosition = 0.5 * (AliMUONConstants::CoilZ() + AliMUONConstants::YokeZ());
+const Double_t AliMUONTrackExtrap::fgkSimpleBLength = 0.5 * (AliMUONConstants::CoilL() + AliMUONConstants::YokeL());
+      Double_t AliMUONTrackExtrap::fgSimpleBValue = 0.;
+      Bool_t   AliMUONTrackExtrap::fgFieldON = kFALSE;
 const Bool_t   AliMUONTrackExtrap::fgkUseHelix = kFALSE;
 const Int_t    AliMUONTrackExtrap::fgkMaxStepNumber = 5000;
 const Double_t AliMUONTrackExtrap::fgkHelixStepLength = 6.;
 const Double_t AliMUONTrackExtrap::fgkRungeKuttaMaxResidue = 0.002;
 
-  //__________________________________________________________________________
+//__________________________________________________________________________
+void AliMUONTrackExtrap::SetField()
+{
+  /// set field on/off flag;  
+  /// set field at the centre of the dipole
+  const Double_t x[3] = {50.,50.,fgkSimpleBPosition};
+  Double_t b[3] = {0.,0.,0.};
+  TGeoGlobalMagField::Instance()->Field(x,b);
+  fgSimpleBValue = b[0];
+  fgFieldON = (TMath::Abs(fgSimpleBValue) > 1.e-10) ? kTRUE : kFALSE;
+  
+}
+
+//__________________________________________________________________________
 Double_t AliMUONTrackExtrap::GetImpactParamFromBendingMomentum(Double_t bendingMomentum)
 {
   /// Returns impact parameter at vertex in bending plane (cm),
@@ -57,21 +73,14 @@ Double_t AliMUONTrackExtrap::GetImpactParamFromBendingMomentum(Double_t bendingM
   
   if (bendingMomentum == 0.) return 1.e10;
   
-  Double_t simpleBPosition = 0.5 * (AliMUONConstants::CoilZ() + AliMUONConstants::YokeZ());
-  Double_t simpleBLength = 0.5 * (AliMUONConstants::CoilL() + AliMUONConstants::YokeL());
-  Float_t b[3], x[3] = {0.,0.,(Float_t) simpleBPosition};
-  if (fgkField) fgkField->Field(x,b);
-  else {
-    cout<<"F-AliMUONTrackExtrap::GetField: fgkField = 0x0"<<endl;
-    exit(-1);
-  }
-  Double_t simpleBValue = (Double_t) b[0];
+  const Double_t kCorrectionFactor = 1.1; // impact parameter is 10% underestimated
   
-  return (-0.0003 * simpleBValue * simpleBLength * simpleBPosition / bendingMomentum);
+  return kCorrectionFactor * (-0.0003 * fgSimpleBValue * fgkSimpleBLength * fgkSimpleBPosition / bendingMomentum);
 }
 
-  //__________________________________________________________________________
-Double_t AliMUONTrackExtrap::GetBendingMomentumFromImpactParam(Double_t impactParam)
+//__________________________________________________________________________
+Double_t 
+AliMUONTrackExtrap::GetBendingMomentumFromImpactParam(Double_t impactParam)
 {
   /// Returns signed bending momentum in bending plane (GeV/c),
   /// the sign being the sign of the charge for particles moving forward in Z,
@@ -80,34 +89,89 @@ Double_t AliMUONTrackExtrap::GetBendingMomentumFromImpactParam(Double_t impactPa
   
   if (impactParam == 0.) return 1.e10;
   
-  Double_t simpleBPosition = 0.5 * (AliMUONConstants::CoilZ() + AliMUONConstants::YokeZ());
-  Double_t simpleBLength = 0.5 * (AliMUONConstants::CoilL() + AliMUONConstants::YokeL());
-  Float_t b[3], x[3] = {0.,0.,(Float_t) simpleBPosition};
-  if (fgkField) fgkField->Field(x,b);
-  else {
-    cout<<"F-AliMUONTrackExtrap::GetField: fgkField = 0x0"<<endl;
-    exit(-1);
+  const Double_t kCorrectionFactor = 1.1; // bending momentum is 10% underestimated
+  
+  if (fgFieldON) 
+  {
+    return kCorrectionFactor * (-0.0003 * fgSimpleBValue * fgkSimpleBLength * fgkSimpleBPosition / impactParam);
+  }
+  else 
+  {
+    return AliMUONConstants::GetMostProbBendingMomentum();
+  }
+}
+
+//__________________________________________________________________________
+void AliMUONTrackExtrap::LinearExtrapToZ(AliMUONTrackParam* trackParam, Double_t zEnd)
+{
+  /// Track parameters linearly extrapolated to the plane at "zEnd".
+  /// On return, results from the extrapolation are updated in trackParam.
+  
+  if (trackParam->GetZ() == zEnd) return; // nothing to be done if same z
+  
+  // Compute track parameters
+  Double_t dZ = zEnd - trackParam->GetZ();
+  trackParam->SetNonBendingCoor(trackParam->GetNonBendingCoor() + trackParam->GetNonBendingSlope() * dZ);
+  trackParam->SetBendingCoor(trackParam->GetBendingCoor() + trackParam->GetBendingSlope() * dZ);
+  trackParam->SetZ(zEnd);
+}
+
+//__________________________________________________________________________
+void AliMUONTrackExtrap::LinearExtrapToZCov(AliMUONTrackParam* trackParam, Double_t zEnd, Bool_t updatePropagator)
+{
+  /// Track parameters and their covariances linearly extrapolated to the plane at "zEnd".
+  /// On return, results from the extrapolation are updated in trackParam.
+  
+  if (trackParam->GetZ() == zEnd) return; // nothing to be done if same z
+  
+  // No need to propagate the covariance matrix if it does not exist
+  if (!trackParam->CovariancesExist()) {
+    cout<<"W-AliMUONTrackExtrap::LinearExtrapToZCov: Covariance matrix does not exist"<<endl;
+    // Extrapolate linearly track parameters to "zEnd"
+    LinearExtrapToZ(trackParam,zEnd);
+    return;
   }
-  Double_t simpleBValue = (Double_t) b[0];
   
-  return (-0.0003 * simpleBValue * simpleBLength * simpleBPosition / impactParam);
+  // Compute track parameters
+  Double_t dZ = zEnd - trackParam->GetZ();
+  trackParam->SetNonBendingCoor(trackParam->GetNonBendingCoor() + trackParam->GetNonBendingSlope() * dZ);
+  trackParam->SetBendingCoor(trackParam->GetBendingCoor() + trackParam->GetBendingSlope() * dZ);
+  trackParam->SetZ(zEnd);
+  
+  // Calculate the jacobian related to the track parameters linear extrapolation to "zEnd"
+  TMatrixD jacob(5,5);
+  jacob.UnitMatrix();
+  jacob(0,1) = dZ;
+  jacob(2,3) = dZ;
+  
+  // Extrapolate track parameter covariances to "zEnd"
+  TMatrixD tmp(trackParam->GetCovariances(),TMatrixD::kMultTranspose,jacob);
+  TMatrixD tmp2(jacob,TMatrixD::kMult,tmp);
+  trackParam->SetCovariances(tmp2);
+  
+  // Update the propagator if required
+  if (updatePropagator) trackParam->UpdatePropagator(jacob);
 }
 
-  //__________________________________________________________________________
-void AliMUONTrackExtrap::ExtrapToZ(AliMUONTrackParam* trackParam, Double_t zEnd)
+//__________________________________________________________________________
+Bool_t AliMUONTrackExtrap::ExtrapToZ(AliMUONTrackParam* trackParam, Double_t zEnd)
 {
   /// Interface to track parameter extrapolation to the plane at "Z" using Helix or Rungekutta algorithm.
   /// On return, the track parameters resulting from the extrapolation are updated in trackParam.
-  if (fgkUseHelix) AliMUONTrackExtrap::ExtrapToZHelix(trackParam,zEnd);
-  else AliMUONTrackExtrap::ExtrapToZRungekutta(trackParam,zEnd);
+  if (!fgFieldON) {
+    AliMUONTrackExtrap::LinearExtrapToZ(trackParam,zEnd);
+    return kTRUE;
+  }
+  else if (fgkUseHelix) return AliMUONTrackExtrap::ExtrapToZHelix(trackParam,zEnd);
+  else return AliMUONTrackExtrap::ExtrapToZRungekutta(trackParam,zEnd);
 }
 
-  //__________________________________________________________________________
-void AliMUONTrackExtrap::ExtrapToZHelix(AliMUONTrackParam* trackParam, Double_t zEnd)
+//__________________________________________________________________________
+Bool_t AliMUONTrackExtrap::ExtrapToZHelix(AliMUONTrackParam* trackParam, Double_t zEnd)
 {
   /// Track parameter extrapolation to the plane at "Z" using Helix algorithm.
   /// On return, the track parameters resulting from the extrapolation are updated in trackParam.
-  if (trackParam->GetZ() == zEnd) return; // nothing to be done if same Z
+  if (trackParam->GetZ() == zEnd) return kTRUE; // nothing to be done if same Z
   Double_t forwardBackward; // +1 if forward, -1 if backward
   if (zEnd < trackParam->GetZ()) forwardBackward = 1.0; // spectro. z<0 
   else forwardBackward = -1.0;
@@ -125,7 +189,7 @@ void AliMUONTrackExtrap::ExtrapToZHelix(AliMUONTrackParam* trackParam, Double_t
     stepNumber++;
     ExtrapOneStepHelix(chargeExtrap, fgkHelixStepLength, v3, v3New);
     if ((-forwardBackward * (v3New[2] - zEnd)) > 0.0) break; // one is beyond Z spectro. z<0
-    // better use TArray ????
+							     // better use TArray ????
     for (i3 = 0; i3 < 7; i3++) {v3[i3] = v3New[i3];}
   }
   // check fgkMaxStepNumber ????
@@ -153,14 +217,15 @@ void AliMUONTrackExtrap::ExtrapToZHelix(AliMUONTrackParam* trackParam, Double_t
   }
   // Recover track parameters (charge back for forward motion)
   RecoverTrackParam(v3, chargeExtrap * forwardBackward, trackParam);
+  return kTRUE;
 }
 
-  //__________________________________________________________________________
-void AliMUONTrackExtrap::ExtrapToZRungekutta(AliMUONTrackParam* trackParam, Double_t zEnd)
+//__________________________________________________________________________
+Bool_t AliMUONTrackExtrap::ExtrapToZRungekutta(AliMUONTrackParam* trackParam, Double_t zEnd)
 {
   /// Track parameter extrapolation to the plane at "Z" using Rungekutta algorithm.
   /// On return, the track parameters resulting from the extrapolation are updated in trackParam.
-  if (trackParam->GetZ() == zEnd) return; // nothing to be done if same Z
+  if (trackParam->GetZ() == zEnd) return kTRUE; // nothing to be done if same Z
   Double_t forwardBackward; // +1 if forward, -1 if backward
   if (zEnd < trackParam->GetZ()) forwardBackward = 1.0; // spectro. z<0 
   else forwardBackward = -1.0;
@@ -171,35 +236,74 @@ void AliMUONTrackExtrap::ExtrapToZRungekutta(AliMUONTrackParam* trackParam, Doub
   Double_t dZ, step;
   Int_t stepNumber = 0;
   
-  // Extrapolation loop (until within tolerance)
+  // Extrapolation loop (until within tolerance or the track turn around)
   Double_t residue = zEnd - trackParam->GetZ();
+  Bool_t uturn = kFALSE;
+  Bool_t trackingFailed = kFALSE;
+  Bool_t tooManyStep = kFALSE;
   while (TMath::Abs(residue) > fgkRungeKuttaMaxResidue && stepNumber <= fgkMaxStepNumber) {
+    
     dZ = zEnd - trackParam->GetZ();
     // step lenght assuming linear trajectory
     step = dZ * TMath::Sqrt(1.0 + trackParam->GetBendingSlope()*trackParam->GetBendingSlope() +
-    			    trackParam->GetNonBendingSlope()*trackParam->GetNonBendingSlope());
+			    trackParam->GetNonBendingSlope()*trackParam->GetNonBendingSlope());
     ConvertTrackParamForExtrap(trackParam, forwardBackward, v3);
+    
     do { // reduce step lenght while zEnd oversteped
       if (stepNumber > fgkMaxStepNumber) {
         cout<<"W-AliMUONTrackExtrap::ExtrapToZRungekutta: Too many trials: "<<stepNumber<<endl;
+	tooManyStep = kTRUE;
 	break;
       }
       stepNumber ++;
       step = TMath::Abs(step);
-      AliMUONTrackExtrap::ExtrapOneStepRungekutta(chargeExtrap,step,v3,v3New);
+      if (!AliMUONTrackExtrap::ExtrapOneStepRungekutta(chargeExtrap,step,v3,v3New)) {
+	trackingFailed = kTRUE;
+	break;
+      }
       residue = zEnd - v3New[2];
       step *= dZ/(v3New[2]-trackParam->GetZ());
     } while (residue*dZ < 0 && TMath::Abs(residue) > fgkRungeKuttaMaxResidue);
-    RecoverTrackParam(v3New, chargeExtrap * forwardBackward, trackParam);
+    
+    if (trackingFailed) break;
+    else if (v3New[5]*v3[5] < 0) { // the track turned around
+      cout<<"W-AliMUONTrackExtrap::ExtrapToZRungekutta: The track turned around"<<endl;
+      uturn = kTRUE;
+      break;
+    } else RecoverTrackParam(v3New, chargeExtrap * forwardBackward, trackParam);
+    
   }
   
   // terminate the extropolation with a straight line up to the exact "zEnd" value
-  trackParam->SetNonBendingCoor(trackParam->GetNonBendingCoor() + residue * trackParam->GetNonBendingSlope());
-  trackParam->SetBendingCoor(trackParam->GetBendingCoor() + residue * trackParam->GetBendingSlope());
-  trackParam->SetZ(zEnd);
+  if (trackingFailed || uturn) {
+    
+    // track ends +-100 meters away in the bending direction
+    dZ = zEnd - v3[2];
+    Double_t bendingSlope = TMath::Sign(1.e4,-fgSimpleBValue*trackParam->GetInverseBendingMomentum()) / dZ;
+    Double_t pZ = TMath::Abs(1. / trackParam->GetInverseBendingMomentum()) / TMath::Sqrt(1.0 + bendingSlope * bendingSlope);
+    Double_t nonBendingSlope = TMath::Sign(TMath::Abs(v3[3]) * v3[6] / pZ, trackParam->GetNonBendingSlope());
+    trackParam->SetNonBendingCoor(trackParam->GetNonBendingCoor() + dZ * nonBendingSlope);
+    trackParam->SetNonBendingSlope(nonBendingSlope);
+    trackParam->SetBendingCoor(trackParam->GetBendingCoor() + dZ * bendingSlope);
+    trackParam->SetBendingSlope(bendingSlope);
+    trackParam->SetZ(zEnd);
+    
+    return kFALSE;
+    
+  } else {
+    
+    // track extrapolated normally
+    trackParam->SetNonBendingCoor(trackParam->GetNonBendingCoor() + residue * trackParam->GetNonBendingSlope());
+    trackParam->SetBendingCoor(trackParam->GetBendingCoor() + residue * trackParam->GetBendingSlope());
+    trackParam->SetZ(zEnd);
+    
+    return !tooManyStep;
+    
+  }
+  
 }
 
-  //__________________________________________________________________________
+//__________________________________________________________________________
 void AliMUONTrackExtrap::ConvertTrackParamForExtrap(AliMUONTrackParam* trackParam, Double_t forwardBackward, Double_t *v3)
 {
   /// Set vector of Geant3 parameters pointed to by "v3" from track parameters in trackParam.
@@ -216,7 +320,7 @@ void AliMUONTrackExtrap::ConvertTrackParamForExtrap(AliMUONTrackParam* trackPara
   v3[4] = trackParam->GetBendingSlope() * v3[5]; // PY/PTOT
 }
 
-  //__________________________________________________________________________
+//__________________________________________________________________________
 void AliMUONTrackExtrap::RecoverTrackParam(Double_t *v3, Double_t charge, AliMUONTrackParam* trackParam)
 {
   /// Set track parameters in trackParam from Geant3 parameters pointed to by "v3",
@@ -225,488 +329,706 @@ void AliMUONTrackExtrap::RecoverTrackParam(Double_t *v3, Double_t charge, AliMUO
   trackParam->SetNonBendingCoor(v3[0]); // X
   trackParam->SetBendingCoor(v3[1]); // Y
   trackParam->SetZ(v3[2]); // Z
-  Double_t pYZ = v3[6] * TMath::Sqrt(1.0 - v3[3] * v3[3]);
+  Double_t pYZ = v3[6] * TMath::Sqrt((1.-v3[3])*(1.+v3[3]));
   trackParam->SetInverseBendingMomentum(charge/pYZ);
   trackParam->SetBendingSlope(v3[4]/v3[5]);
   trackParam->SetNonBendingSlope(v3[3]/v3[5]);
 }
 
-  //__________________________________________________________________________
-void AliMUONTrackExtrap::ExtrapToZCov(AliMUONTrackParam* trackParam, Double_t zEnd)
+//__________________________________________________________________________
+Bool_t AliMUONTrackExtrap::ExtrapToZCov(AliMUONTrackParam* trackParam, Double_t zEnd, Bool_t updatePropagator)
 {
   /// Track parameters and their covariances extrapolated to the plane at "zEnd".
   /// On return, results from the extrapolation are updated in trackParam.
   
-  if (trackParam->GetZ() == zEnd) return; // nothing to be done if same z
+  if (trackParam->GetZ() == zEnd) return kTRUE; // nothing to be done if same z
+  
+  if (!fgFieldON) { // linear extrapolation if no magnetic field
+    AliMUONTrackExtrap::LinearExtrapToZCov(trackParam,zEnd,updatePropagator);
+    return kTRUE;
+  }
+  
+  // No need to propagate the covariance matrix if it does not exist
+  if (!trackParam->CovariancesExist()) {
+    cout<<"W-AliMUONTrackExtrap::ExtrapToZCov: Covariance matrix does not exist"<<endl;
+    // Extrapolate track parameters to "zEnd"
+    return ExtrapToZ(trackParam,zEnd);
+  }
   
   // Save the actual track parameters
   AliMUONTrackParam trackParamSave(*trackParam);
-  Double_t nonBendingCoor 	  = trackParamSave.GetNonBendingCoor();
-  Double_t nonBendingSlope 	  = trackParamSave.GetNonBendingSlope();
-  Double_t bendingCoor 		  = trackParamSave.GetBendingCoor();
-  Double_t bendingSlope 	  = trackParamSave.GetBendingSlope();
-  Double_t inverseBendingMomentum = trackParamSave.GetInverseBendingMomentum();
-  Double_t zBegin		  = trackParamSave.GetZ();
+  TMatrixD paramSave(trackParamSave.GetParameters());
+  Double_t zBegin = trackParamSave.GetZ();
   
+  // Get reference to the parameter covariance matrix
+  const TMatrixD& kParamCov = trackParam->GetCovariances();
+	
   // Extrapolate track parameters to "zEnd"
-  ExtrapToZ(trackParam,zEnd);
-  Double_t extrapNonBendingCoor 	= trackParam->GetNonBendingCoor();
-  Double_t extrapNonBendingSlope 	= trackParam->GetNonBendingSlope();
-  Double_t extrapBendingCoor 		= trackParam->GetBendingCoor();
-  Double_t extrapBendingSlope		= trackParam->GetBendingSlope();
-  Double_t extrapInverseBendingMomentum = trackParam->GetInverseBendingMomentum();
-  
-  // Get the pointer to the parameter covariance matrix
-  if (!trackParam->CovariancesExist()) {
-    //cout<<"W-AliMUONTrackExtrap::ExtrapToZCov: track parameter covariance matrix does not exist"<<endl;
-    //cout<<"                                    -> nothing to extrapolate !!"<<endl;
-    return;
-  }
-  TMatrixD* paramCov = trackParam->GetCovariances();
+  // Do not update the covariance matrix if the extrapolation failed
+  if (!ExtrapToZ(trackParam,zEnd)) return kFALSE;
+  
+  // Get reference to the extrapolated parameters
+  const TMatrixD& extrapParam = trackParam->GetParameters();
   
   // Calculate the jacobian related to the track parameters extrapolation to "zEnd"
+  Bool_t extrapStatus = kTRUE;
   TMatrixD jacob(5,5);
-  jacob = 0.;
-  Double_t dParam[5];
+  jacob.Zero();
+  TMatrixD dParam(5,1);
+  Double_t direction[5] = {-1.,-1.,1.,1.,-1.};
   for (Int_t i=0; i<5; i++) {
     // Skip jacobian calculation for parameters with no associated error
-    if ((*paramCov)(i,i) == 0.) continue;
+    if (kParamCov(i,i) <= 0.) continue;
+    
     // Small variation of parameter i only
     for (Int_t j=0; j<5; j++) {
       if (j==i) {
-        dParam[j] = TMath::Sqrt((*paramCov)(i,i));
-	if (j == 4) dParam[j] *= TMath::Sign(1.,-inverseBendingMomentum); // variation always in the same direction
-      } else dParam[j] = 0.;
+        dParam(j,0) = TMath::Sqrt(kParamCov(i,i));
+	dParam(j,0) *= TMath::Sign(1.,direction[j]*paramSave(j,0)); // variation always in the same direction
+      } else dParam(j,0) = 0.;
     }
+    
     // Set new parameters
-    trackParamSave.SetNonBendingCoor	    (nonBendingCoor	    + dParam[0]);
-    trackParamSave.SetNonBendingSlope	    (nonBendingSlope	    + dParam[1]);
-    trackParamSave.SetBendingCoor	    (bendingCoor	    + dParam[2]);
-    trackParamSave.SetBendingSlope	    (bendingSlope	    + dParam[3]);
-    trackParamSave.SetInverseBendingMomentum(inverseBendingMomentum + dParam[4]);
-    trackParamSave.SetZ			    (zBegin);
+    trackParamSave.SetParameters(paramSave);
+    trackParamSave.AddParameters(dParam);
+    trackParamSave.SetZ(zBegin);
+    
     // Extrapolate new track parameters to "zEnd"
-    ExtrapToZ(&trackParamSave,zEnd);
+    if (!ExtrapToZ(&trackParamSave,zEnd)) {
+      cout<<"W-AliMUONTrackExtrap::ExtrapToZCov: Bad covariance matrix"<<endl;
+      extrapStatus = kFALSE;
+    }
+    
     // Calculate the jacobian
-    jacob(0,i) = (trackParamSave.GetNonBendingCoor()	     - extrapNonBendingCoor 	   ) / dParam[i];
-    jacob(1,i) = (trackParamSave.GetNonBendingSlope()	     - extrapNonBendingSlope 	   ) / dParam[i];
-    jacob(2,i) = (trackParamSave.GetBendingCoor()	     - extrapBendingCoor    	   ) / dParam[i];
-    jacob(3,i) = (trackParamSave.GetBendingSlope()	     - extrapBendingSlope   	   ) / dParam[i];
-    jacob(4,i) = (trackParamSave.GetInverseBendingMomentum() - extrapInverseBendingMomentum) / dParam[i];
+    TMatrixD jacobji(trackParamSave.GetParameters(),TMatrixD::kMinus,extrapParam);
+    jacobji *= 1. / dParam(i,0);
+    jacob.SetSub(0,i,jacobji);
   }
   
   // Extrapolate track parameter covariances to "zEnd"
-  TMatrixD tmp((*paramCov),TMatrixD::kMultTranspose,jacob);
-  (*paramCov) = TMatrixD(jacob,TMatrixD::kMult,tmp);
+  TMatrixD tmp(kParamCov,TMatrixD::kMultTranspose,jacob);
+  TMatrixD tmp2(jacob,TMatrixD::kMult,tmp);
+  trackParam->SetCovariances(tmp2);
+  
+  // Update the propagator if required
+  if (updatePropagator) trackParam->UpdatePropagator(jacob);
   
+  return extrapStatus;
 }
 
-  //__________________________________________________________________________
-void AliMUONTrackExtrap::ExtrapToStation(AliMUONTrackParam* trackParamIn, Int_t station, AliMUONTrackParam *trackParamOut)
+//__________________________________________________________________________
+void AliMUONTrackExtrap::AddMCSEffectInAbsorber(AliMUONTrackParam* param, Double_t signedPathLength, Double_t f0, Double_t f1, Double_t f2)
 {
-  /// Track parameters extrapolated from "trackParamIn" to both chambers of the station(0..) "station"
-  /// are returned in the array (dimension 2) of track parameters pointed to by "TrackParamOut"
-  /// (index 0 and 1 for first and second chambers).
-  Double_t extZ[2], z1, z2;
-  Int_t i1 = -1, i2 = -1; // = -1 to avoid compilation warnings
-  // range of station to be checked ????
-  z1 = AliMUONConstants::DefaultChamberZ(2 * station);
-  z2 = AliMUONConstants::DefaultChamberZ(2 * station + 1);
-  // First and second Z to extrapolate at
-  if ((z1 > trackParamIn->GetZ()) && (z2 > trackParamIn->GetZ())) {i1 = 0; i2 = 1;}
-  else if ((z1 < trackParamIn->GetZ()) && (z2 < trackParamIn->GetZ())) {i1 = 1; i2 = 0;}
-  else {
-    cout<<"E-AliMUONTrackExtrap::ExtrapToStation: Starting Z ("<<trackParamIn->GetZ()
-    	<<") in between z1 ("<<z1<<") and z2 ("<<z2<<") of station(0..)"<<station<<endl;
-    exit(-1);
+  /// Add to the track parameter covariances the effects of multiple Coulomb scattering
+  /// signedPathLength must have the sign of (zOut - zIn) where all other parameters are assumed to be given at zOut.
+  
+  // absorber related covariance parameters
+  Double_t bendingSlope = param->GetBendingSlope();
+  Double_t nonBendingSlope = param->GetNonBendingSlope();
+  Double_t inverseBendingMomentum = param->GetInverseBendingMomentum();
+  Double_t alpha2 = 0.0136 * 0.0136 * inverseBendingMomentum * inverseBendingMomentum * (1.0 + bendingSlope * bendingSlope) /
+                    (1.0 + bendingSlope *bendingSlope + nonBendingSlope * nonBendingSlope); // velocity = 1
+  Double_t pathLength = TMath::Abs(signedPathLength);
+  Double_t varCoor = alpha2 * (pathLength * pathLength * f0 - 2. * pathLength * f1 + f2);
+  Double_t covCorrSlope = TMath::Sign(1.,signedPathLength) * alpha2 * (pathLength * f0 - f1);
+  Double_t varSlop = alpha2 * f0;
+  
+  // Set MCS covariance matrix
+  TMatrixD newParamCov(param->GetCovariances());
+  // Non bending plane
+  newParamCov(0,0) += varCoor;       newParamCov(0,1) += covCorrSlope;
+  newParamCov(1,0) += covCorrSlope;  newParamCov(1,1) += varSlop;
+  // Bending plane
+  newParamCov(2,2) += varCoor;       newParamCov(2,3) += covCorrSlope;
+  newParamCov(3,2) += covCorrSlope;  newParamCov(3,3) += varSlop;
+  
+  // Set momentum related covariances if B!=0
+  if (fgFieldON) {
+    // compute derivative d(q/Pxy) / dSlopeX and d(q/Pxy) / dSlopeY
+    Double_t dqPxydSlopeX = inverseBendingMomentum * nonBendingSlope / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
+    Double_t dqPxydSlopeY = - inverseBendingMomentum * nonBendingSlope*nonBendingSlope * bendingSlope /
+                              (1. + bendingSlope*bendingSlope) / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
+    // Inverse bending momentum (due to dependences with bending and non bending slopes)
+    newParamCov(4,0) += dqPxydSlopeX * covCorrSlope; newParamCov(0,4) += dqPxydSlopeX * covCorrSlope;
+    newParamCov(4,1) += dqPxydSlopeX * varSlop;      newParamCov(1,4) += dqPxydSlopeX * varSlop;
+    newParamCov(4,2) += dqPxydSlopeY * covCorrSlope; newParamCov(2,4) += dqPxydSlopeY * covCorrSlope;
+    newParamCov(4,3) += dqPxydSlopeY * varSlop;      newParamCov(3,4) += dqPxydSlopeY * varSlop;
+    newParamCov(4,4) += (dqPxydSlopeX*dqPxydSlopeX + dqPxydSlopeY*dqPxydSlopeY) * varSlop;
   }
-  extZ[i1] = z1;
-  extZ[i2] = z2;
-  // copy of track parameters
-  trackParamOut[i1] = *trackParamIn;
-  // first extrapolation
-  ExtrapToZ(&(trackParamOut[i1]),extZ[0]);
-  trackParamOut[i2] = trackParamOut[i1];
-  // second extrapolation
-  ExtrapToZ(&(trackParamOut[i2]),extZ[1]);
-  return;
+  
+  // Set new covariances
+  param->SetCovariances(newParamCov);
 }
 
-  //__________________________________________________________________________
-void AliMUONTrackExtrap::ExtrapToVertexUncorrected(AliMUONTrackParam* trackParam, Double_t zVtx)
+//__________________________________________________________________________
+void AliMUONTrackExtrap::CorrectMCSEffectInAbsorber(AliMUONTrackParam* param,
+						    Double_t xVtx, Double_t yVtx, Double_t zVtx,
+						    Double_t errXVtx, Double_t errYVtx,
+						    Double_t absZBeg, Double_t pathLength, Double_t f0, Double_t f1, Double_t f2)
 {
-  /// Extrapolation to the vertex (at the z position "zVtx") without Branson and Field correction.
-  /// Returns the track parameters resulting from the extrapolation in the current TrackParam.
-  /// Include multiple Coulomb scattering effects in trackParam covariances.
+  /// Correct parameters and corresponding covariances using Branson correction
+  /// - input param are parameters and covariances at the end of absorber
+  /// - output param are parameters and covariances at vertex
+  /// Absorber correction parameters are supposed to be calculated at the current track z-position
   
-  if (trackParam->GetZ() > zVtx) { // spectro. (z<0)
-    cout<<"W-AliMUONTrackExtrap::ExtrapToVertexUncorrected: Starting Z ("<<trackParam->GetZ()
-    	<<") upstream the vertex (zVtx = "<<zVtx<<")"<<endl;
-    exit(-1);
-  }
+  // Position of the Branson plane (spectro. (z<0))
+  Double_t zB = (f1>0.) ? absZBeg - f2/f1 : 0.;
   
-  if (zVtx < AliMUONConstants::ZAbsorberEnd()) { // spectro. (z<0)
-    cout<<"W-AliMUONTrackExtrap::ExtrapToVertexUncorrected: Ending Z ("<<zVtx
-    	<<") downstream the front absorber (zAbsorberEnd = "<<AliMUONConstants::ZAbsorberEnd()<<")"<<endl;
-    
-    ExtrapToZCov(trackParam,zVtx);
-    return;
+  // Add MCS effects to current parameter covariances (spectro. (z<0))
+  AddMCSEffectInAbsorber(param, -pathLength, f0, f1, f2);
+  
+  // Get track parameters and covariances in the Branson plane corrected for magnetic field effect
+  ExtrapToZCov(param,zVtx);
+  LinearExtrapToZCov(param,zB);
+  
+  // compute track parameters at vertex
+  TMatrixD newParam(5,1);
+  newParam(0,0) = xVtx;
+  newParam(1,0) = (param->GetNonBendingCoor() - xVtx) / (zB - zVtx);
+  newParam(2,0) = yVtx;
+  newParam(3,0) = (param->GetBendingCoor() - yVtx) / (zB - zVtx);
+  newParam(4,0) = param->GetCharge() / param->P() *
+                  TMath::Sqrt(1.0 + newParam(1,0)*newParam(1,0) + newParam(3,0)*newParam(3,0)) /
+		  TMath::Sqrt(1.0 + newParam(3,0)*newParam(3,0));
+  
+  // Get covariances in (X, SlopeX, Y, SlopeY, q*PTot) coordinate system
+  TMatrixD paramCovP(param->GetCovariances());
+  Cov2CovP(param->GetParameters(),paramCovP);
+  
+  // Get the covariance matrix in the (XVtx, X, YVtx, Y, q*PTot) coordinate system
+  TMatrixD paramCovVtx(5,5);
+  paramCovVtx.Zero();
+  paramCovVtx(0,0) = errXVtx * errXVtx;
+  paramCovVtx(1,1) = paramCovP(0,0);
+  paramCovVtx(2,2) = errYVtx * errYVtx;
+  paramCovVtx(3,3) = paramCovP(2,2);
+  paramCovVtx(4,4) = paramCovP(4,4);
+  paramCovVtx(1,3) = paramCovP(0,2);
+  paramCovVtx(3,1) = paramCovP(2,0);
+  paramCovVtx(1,4) = paramCovP(0,4);
+  paramCovVtx(4,1) = paramCovP(4,0);
+  paramCovVtx(3,4) = paramCovP(2,4);
+  paramCovVtx(4,3) = paramCovP(4,2);
+  
+  // Jacobian of the transformation (XVtx, X, YVtx, Y, q*PTot) -> (XVtx, SlopeXVtx, YVtx, SlopeYVtx, q*PTotVtx)
+  TMatrixD jacob(5,5);
+  jacob.UnitMatrix();
+  jacob(1,0) = - 1. / (zB - zVtx);
+  jacob(1,1) = 1. / (zB - zVtx);
+  jacob(3,2) = - 1. / (zB - zVtx);
+  jacob(3,3) = 1. / (zB - zVtx);
+  
+  // Compute covariances at vertex in the (XVtx, SlopeXVtx, YVtx, SlopeYVtx, q*PTotVtx) coordinate system
+  TMatrixD tmp(paramCovVtx,TMatrixD::kMultTranspose,jacob);
+  TMatrixD newParamCov(jacob,TMatrixD::kMult,tmp);
+  
+  // Compute covariances at vertex in the (XVtx, SlopeXVtx, YVtx, SlopeYVtx, q/PyzVtx) coordinate system
+  CovP2Cov(newParam,newParamCov);
+  
+  // Set parameters and covariances at vertex
+  param->SetParameters(newParam);
+  param->SetZ(zVtx);
+  param->SetCovariances(newParamCov);
+}
+
+//__________________________________________________________________________
+void AliMUONTrackExtrap::CorrectELossEffectInAbsorber(AliMUONTrackParam* param, Double_t eLoss, Double_t sigmaELoss2)
+{
+  /// Correct parameters for energy loss and add energy loss fluctuation effect to covariances
+  
+  // Get parameter covariances in (X, SlopeX, Y, SlopeY, q*PTot) coordinate system
+  TMatrixD newParamCov(param->GetCovariances());
+  Cov2CovP(param->GetParameters(),newParamCov);
+  
+  // Compute new parameters corrected for energy loss
+  Double_t muMass = TDatabasePDG::Instance()->GetParticle("mu-")->Mass(); // GeV
+  Double_t p = param->P();
+  Double_t e = TMath::Sqrt(p*p + muMass*muMass);
+  Double_t eCorr = e + eLoss;
+  Double_t pCorr = TMath::Sqrt(eCorr*eCorr - muMass*muMass);
+  Double_t nonBendingSlope = param->GetNonBendingSlope();
+  Double_t bendingSlope = param->GetBendingSlope();
+  param->SetInverseBendingMomentum(param->GetCharge() / pCorr *
+				   TMath::Sqrt(1.0 + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope) /
+				   TMath::Sqrt(1.0 + bendingSlope*bendingSlope));
+  
+  // Add effects of energy loss fluctuation to covariances
+  newParamCov(4,4) += eCorr * eCorr / pCorr / pCorr * sigmaELoss2;
+  
+  // Get new parameter covariances in (X, SlopeX, Y, SlopeY, q/Pyz) coordinate system
+  CovP2Cov(param->GetParameters(),newParamCov);
+  
+  // Set new parameter covariances
+  param->SetCovariances(newParamCov);
+}
+
+//__________________________________________________________________________
+Bool_t AliMUONTrackExtrap::GetAbsorberCorrectionParam(Double_t trackXYZIn[3], Double_t trackXYZOut[3], Double_t pTotal,
+						      Double_t &pathLength, Double_t &f0, Double_t &f1, Double_t &f2,
+						      Double_t &meanRho, Double_t &totalELoss, Double_t &sigmaELoss2)
+{
+  /// Parameters used to correct for Multiple Coulomb Scattering and energy loss in absorber
+  /// Calculated assuming a linear propagation from trackXYZIn to trackXYZOut (order is important)
+  // pathLength: path length between trackXYZIn and trackXYZOut (cm)
+  // f0:         0th moment of z calculated with the inverse radiation-length distribution
+  // f1:         1st moment of z calculated with the inverse radiation-length distribution
+  // f2:         2nd moment of z calculated with the inverse radiation-length distribution
+  // meanRho:    average density of crossed material (g/cm3)
+  // totalELoss: total energy loss in absorber
+  
+  // Reset absorber's parameters
+  pathLength = 0.;
+  f0 = 0.;
+  f1 = 0.;
+  f2 = 0.;
+  meanRho = 0.;
+  totalELoss = 0.;
+  sigmaELoss2 = 0.;
+  
+  // Check whether the geometry is available
+  if (!gGeoManager) {
+    cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: no TGeo"<<endl;
+    return kFALSE;
   }
   
-  // First Extrapolates track parameters upstream to the "Z" end of the front absorber
-  if (trackParam->GetZ() < AliMUONConstants::ZAbsorberEnd()) { // spectro. (z<0)
-    ExtrapToZCov(trackParam,AliMUONConstants::ZAbsorberEnd());
-  } else {
-    cout<<"W-AliMUONTrackExtrap::ExtrapToVertexUncorrected: Starting Z ("<<trackParam->GetZ()
-    	<<") upstream or inside the front absorber (zAbsorberEnd = "<<AliMUONConstants::ZAbsorberEnd()<<")"<<endl;
+  // Initialize starting point and direction
+  pathLength = TMath::Sqrt((trackXYZOut[0] - trackXYZIn[0])*(trackXYZOut[0] - trackXYZIn[0])+
+			   (trackXYZOut[1] - trackXYZIn[1])*(trackXYZOut[1] - trackXYZIn[1])+
+			   (trackXYZOut[2] - trackXYZIn[2])*(trackXYZOut[2] - trackXYZIn[2]));
+  if (pathLength < TGeoShape::Tolerance()) return kFALSE;
+  Double_t b[3];
+  b[0] = (trackXYZOut[0] - trackXYZIn[0]) / pathLength;
+  b[1] = (trackXYZOut[1] - trackXYZIn[1]) / pathLength;
+  b[2] = (trackXYZOut[2] - trackXYZIn[2]) / pathLength;
+  TGeoNode *currentnode = gGeoManager->InitTrack(trackXYZIn, b);
+  if (!currentnode) {
+    cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: start point out of geometry"<<endl;
+    return kFALSE;
   }
   
-  // Then go through all the absorber layers
-  Double_t tan3 = TMath::Tan(3./180.*TMath::Pi());
-  Double_t r0Norm, x0, z, zElement, dZ, nonBendingCoor, bendingCoor;
-  for (Int_t iElement=AliMUONConstants::NAbsorberElements()-1; iElement>=0; iElement--) {
-    zElement = AliMUONConstants::ZAbsorberElement(iElement);
-    z = trackParam->GetZ();
-    if (z > zElement) continue; // spectro. (z<0)
-    nonBendingCoor = trackParam->GetNonBendingCoor();
-    bendingCoor = trackParam->GetBendingCoor();
-    r0Norm = nonBendingCoor * nonBendingCoor + bendingCoor * bendingCoor;
-    r0Norm  = TMath::Sqrt(r0Norm) / TMath::Abs(trackParam->GetZ()) / tan3;
-    if (r0Norm > 1.) x0 = AliMUONConstants::X0AbsorberOut(iElement); // outer part of the absorber
-    else x0 = AliMUONConstants::X0AbsorberIn(iElement); // inner part of the absorber
+  // loop over absorber slices and calculate absorber's parameters
+  Double_t rho = 0.; // material density (g/cm3)
+  Double_t x0 = 0.;  // radiation-length (cm-1)
+  Double_t atomicA = 0.; // A of material
+  Double_t atomicZ = 0.; // Z of material
+  Double_t atomicZoverA = 0.; // Z/A of material
+  Double_t localPathLength = 0;
+  Double_t remainingPathLength = pathLength;
+  Double_t zB = trackXYZIn[2];
+  Double_t zE, dzB, dzE;
+  do {
+    // Get material properties
+    TGeoMaterial *material = currentnode->GetVolume()->GetMedium()->GetMaterial();
+    rho = material->GetDensity();
+    x0 = material->GetRadLen();
+    atomicA = material->GetA();
+    atomicZ = material->GetZ();
+    if(material->IsMixture()){
+      TGeoMixture * mixture = (TGeoMixture*)material;
+      atomicZoverA = 0.;
+      Double_t sum = 0.;
+      for (Int_t iel=0;iel<mixture->GetNelements();iel++){
+	sum  += mixture->GetWmixt()[iel];
+	atomicZoverA += mixture->GetZmixt()[iel]*mixture->GetWmixt()[iel]/mixture->GetAmixt()[iel];
+      }
+      atomicZoverA/=sum;
+    }
+    else atomicZoverA = atomicZ/atomicA;
     
-    if (zVtx > zElement) {
-      ExtrapToZCov(trackParam,zElement); // extrapolate to absorber element "iElement"
-      dZ = zElement - z;
-      AddMCSEffectInTrackParamCov(trackParam,dZ,x0); // include MCS effect in covariances
-    } else {
-      ExtrapToZCov(trackParam,zVtx); // extrapolate to zVtx
-      dZ = zVtx - z;
-      AddMCSEffectInTrackParamCov(trackParam,dZ,x0); // include MCS effect in covariances
-      break;
+    // Get path length within this material
+    gGeoManager->FindNextBoundary(remainingPathLength);
+    localPathLength = gGeoManager->GetStep() + 1.e-6;
+    // Check if boundary within remaining path length. If so, make sure to cross the boundary to prepare the next step
+    if (localPathLength >= remainingPathLength) localPathLength = remainingPathLength;
+    else {
+      currentnode = gGeoManager->Step();
+      if (!currentnode) {
+        cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: navigation failed"<<endl;
+	f0 = f1 = f2 = meanRho = totalELoss = sigmaELoss2 = 0.;
+	return kFALSE;
+      }
+      if (!gGeoManager->IsEntering()) {
+        // make another small step to try to enter in new absorber slice
+        gGeoManager->SetStep(0.001);
+	currentnode = gGeoManager->Step();
+	if (!gGeoManager->IsEntering() || !currentnode) {
+          cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: navigation failed"<<endl;
+	  f0 = f1 = f2 = meanRho = totalELoss = sigmaELoss2 = 0.;
+	  return kFALSE;
+	}
+        localPathLength += 0.001;
+      }
     }
-  }
+    
+    // calculate absorber's parameters
+    zE = b[2] * localPathLength + zB;
+    dzB = zB - trackXYZIn[2];
+    dzE = zE - trackXYZIn[2];
+    f0 += localPathLength / x0;
+    f1 += (dzE*dzE - dzB*dzB) / b[2] / b[2] / x0 / 2.;
+    f2 += (dzE*dzE*dzE - dzB*dzB*dzB) / b[2] / b[2] / b[2] / x0 / 3.;
+    meanRho += localPathLength * rho;
+    totalELoss += BetheBloch(pTotal, localPathLength, rho, atomicZ, atomicZoverA);
+    sigmaELoss2 += EnergyLossFluctuation2(pTotal, localPathLength, rho, atomicZoverA);
+    
+    // prepare next step
+    zB = zE;
+    remainingPathLength -= localPathLength;
+  } while (remainingPathLength > TGeoShape::Tolerance());
   
-  // finally go to the vertex
-  ExtrapToZCov(trackParam,zVtx);
+  meanRho /= pathLength;
   
+  return kTRUE;
 }
 
-  //__________________________________________________________________________
-void AliMUONTrackExtrap::AddMCSEffectInTrackParamCov(AliMUONTrackParam *param, Double_t dZ, Double_t x0)
+//__________________________________________________________________________
+Double_t AliMUONTrackExtrap::GetMCSAngle2(const AliMUONTrackParam& param, Double_t dZ, Double_t x0)
 {
-  /// Add to the track parameter covariances the effects of multiple Coulomb scattering
+  /// Return the angular dispersion square due to multiple Coulomb scattering
   /// through a material of thickness "dZ" and of radiation length "x0"
   /// assuming linear propagation and using the small angle approximation.
   
-  Double_t bendingSlope = param->GetBendingSlope();
-  Double_t nonBendingSlope = param->GetNonBendingSlope();
-  Double_t inverseTotalMomentum2 = param->GetInverseBendingMomentum() * param->GetInverseBendingMomentum() *
-  				   (1.0 + bendingSlope * bendingSlope) /
-			  	   (1.0 + bendingSlope *bendingSlope + nonBendingSlope * nonBendingSlope); 
+  Double_t bendingSlope = param.GetBendingSlope();
+  Double_t nonBendingSlope = param.GetNonBendingSlope();
+  Double_t inverseTotalMomentum2 = param.GetInverseBendingMomentum() * param.GetInverseBendingMomentum() *
+                                   (1.0 + bendingSlope * bendingSlope) /
+                                   (1.0 + bendingSlope *bendingSlope + nonBendingSlope * nonBendingSlope); 
   // Path length in the material
   Double_t pathLength = TMath::Abs(dZ) * TMath::Sqrt(1.0 + bendingSlope*bendingSlope + nonBendingSlope*nonBendingSlope);
-  Double_t pathLength2 = pathLength * pathLength;
   // relativistic velocity
   Double_t velo = 1.;
   // Angular dispersion square of the track (variance) in a plane perpendicular to the trajectory
   Double_t theta02 = 0.0136 / velo * (1 + 0.038 * TMath::Log(pathLength/x0));
-  theta02 *= theta02 * inverseTotalMomentum2 * pathLength / x0;
   
-  // Add effects of multiple Coulomb scattering in track parameter covariances
-  TMatrixD* paramCov = param->GetCovariances();
-  Double_t varCoor 	= pathLength2 * theta02 / 3.;
+  return theta02 * theta02 * inverseTotalMomentum2 * pathLength / x0;
+}
+
+//__________________________________________________________________________
+void AliMUONTrackExtrap::AddMCSEffect(AliMUONTrackParam *param, Double_t dZ, Double_t x0)
+{
+  /// Add to the track parameter covariances the effects of multiple Coulomb scattering
+  /// through a material of thickness "Abs(dZ)" and of radiation length "x0"
+  /// assuming linear propagation and using the small angle approximation.
+  /// dZ = zOut - zIn (sign is important) and "param" is assumed to be given zOut.
+  /// If x0 <= 0., assume dZ = pathLength/x0 and consider the material thickness as negligible.
+  
+  Double_t bendingSlope = param->GetBendingSlope();
+  Double_t nonBendingSlope = param->GetNonBendingSlope();
+  Double_t inverseBendingMomentum = param->GetInverseBendingMomentum();
+  Double_t inverseTotalMomentum2 = inverseBendingMomentum * inverseBendingMomentum *
+                                   (1.0 + bendingSlope * bendingSlope) /
+                                   (1.0 + bendingSlope *bendingSlope + nonBendingSlope * nonBendingSlope); 
+  // Path length in the material
+  Double_t signedPathLength = dZ * TMath::Sqrt(1.0 + bendingSlope*bendingSlope + nonBendingSlope*nonBendingSlope);
+  Double_t pathLengthOverX0 = (x0 > 0.) ? TMath::Abs(signedPathLength) / x0 : TMath::Abs(signedPathLength);
+  // relativistic velocity
+  Double_t velo = 1.;
+  // Angular dispersion square of the track (variance) in a plane perpendicular to the trajectory
+  Double_t theta02 = 0.0136 / velo * (1 + 0.038 * TMath::Log(pathLengthOverX0));
+  theta02 *= theta02 * inverseTotalMomentum2 * pathLengthOverX0;
+  
+  Double_t varCoor 	= (x0 > 0.) ? signedPathLength * signedPathLength * theta02 / 3. : 0.;
   Double_t varSlop 	= theta02;
-  Double_t covCorrSlope = pathLength * theta02 / 2.;
+  Double_t covCorrSlope = (x0 > 0.) ? signedPathLength * theta02 / 2. : 0.;
+  
+  // Set MCS covariance matrix
+  TMatrixD newParamCov(param->GetCovariances());
   // Non bending plane
-  (*paramCov)(0,0) += varCoor;		(*paramCov)(0,1) += covCorrSlope;
-  (*paramCov)(1,0) += covCorrSlope;	(*paramCov)(1,1) += varSlop;
+  newParamCov(0,0) += varCoor;       newParamCov(0,1) += covCorrSlope;
+  newParamCov(1,0) += covCorrSlope;  newParamCov(1,1) += varSlop;
   // Bending plane
-  (*paramCov)(2,2) += varCoor;		(*paramCov)(2,3) += covCorrSlope;
-  (*paramCov)(3,2) += covCorrSlope;	(*paramCov)(3,3) += varSlop;
+  newParamCov(2,2) += varCoor;       newParamCov(2,3) += covCorrSlope;
+  newParamCov(3,2) += covCorrSlope;  newParamCov(3,3) += varSlop;
   
+  // Set momentum related covariances if B!=0
+  if (fgFieldON) {
+    // compute derivative d(q/Pxy) / dSlopeX and d(q/Pxy) / dSlopeY
+    Double_t dqPxydSlopeX = inverseBendingMomentum * nonBendingSlope / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
+    Double_t dqPxydSlopeY = - inverseBendingMomentum * nonBendingSlope*nonBendingSlope * bendingSlope /
+                              (1. + bendingSlope*bendingSlope) / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
+    // Inverse bending momentum (due to dependences with bending and non bending slopes)
+    newParamCov(4,0) += dqPxydSlopeX * covCorrSlope; newParamCov(0,4) += dqPxydSlopeX * covCorrSlope;
+    newParamCov(4,1) += dqPxydSlopeX * varSlop;      newParamCov(1,4) += dqPxydSlopeX * varSlop;
+    newParamCov(4,2) += dqPxydSlopeY * covCorrSlope; newParamCov(2,4) += dqPxydSlopeY * covCorrSlope;
+    newParamCov(4,3) += dqPxydSlopeY * varSlop;      newParamCov(3,4) += dqPxydSlopeY * varSlop;
+    newParamCov(4,4) += (dqPxydSlopeX*dqPxydSlopeX + dqPxydSlopeY*dqPxydSlopeY) * varSlop;
+  }
+  
+  // Set new covariances
+  param->SetCovariances(newParamCov);
 }
 
-  //__________________________________________________________________________
-void AliMUONTrackExtrap::ExtrapToVertex(AliMUONTrackParam* trackParam, Double_t xVtx, Double_t yVtx, Double_t zVtx)
+//__________________________________________________________________________
+void AliMUONTrackExtrap::ExtrapToVertex(AliMUONTrackParam* trackParam,
+					Double_t xVtx, Double_t yVtx, Double_t zVtx,
+					Double_t errXVtx, Double_t errYVtx,
+					Bool_t correctForMCS, Bool_t correctForEnergyLoss)
 {
-  /// Extrapolation to the vertex.
-  /// Returns the track parameters resulting from the extrapolation in the current TrackParam.
-  /// Changes parameters according to Branson correction through the absorber 
-  
-  // Extrapolates track parameters upstream to the "Z" end of the front absorber
-  ExtrapToZ(trackParam,AliMUONConstants::ZAbsorberEnd()); // !!!
-  // Makes Branson correction (multiple scattering + energy loss)
-  BransonCorrection(trackParam,xVtx,yVtx,zVtx);
-  // Makes a simple magnetic field correction through the absorber
-  FieldCorrection(trackParam,AliMUONConstants::ZAbsorberEnd());
+  /// Main method for extrapolation to the vertex:
+  /// Returns the track parameters and covariances resulting from the extrapolation of the current trackParam
+  /// Changes parameters and covariances according to multiple scattering and energy loss corrections:
+  /// if correctForMCS=kTRUE:  compute parameters using Branson correction and add correction resolution to covariances
+  /// if correctForMCS=kFALSE: add parameter dispersion due to MCS in parameter covariances
+  /// if correctForEnergyLoss=kTRUE:  correct parameters for energy loss and add energy loss fluctuation to covariances
+  /// if correctForEnergyLoss=kFALSE: do nothing about energy loss
+  
+  if (trackParam->GetZ() == zVtx) return; // nothing to be done if already at vertex
+  
+  if (trackParam->GetZ() > zVtx) { // spectro. (z<0)
+    cout<<"E-AliMUONTrackExtrap::ExtrapToVertex: Starting Z ("<<trackParam->GetZ()
+        <<") upstream the vertex (zVtx = "<<zVtx<<")"<<endl;
+    return;
+  }
+  
+  // Check the vertex position relatively to the absorber
+  if (zVtx < AliMUONConstants::AbsZBeg() && zVtx > AliMUONConstants::AbsZEnd()) { // spectro. (z<0)
+    cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Ending Z ("<<zVtx
+        <<") inside the front absorber ("<<AliMUONConstants::AbsZBeg()<<","<<AliMUONConstants::AbsZEnd()<<")"<<endl;
+  } else if (zVtx < AliMUONConstants::AbsZEnd() ) { // spectro. (z<0)
+    cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Ending Z ("<<zVtx
+        <<") downstream the front absorber (zAbsorberEnd = "<<AliMUONConstants::AbsZEnd()<<")"<<endl;
+    if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,zVtx);
+    else ExtrapToZ(trackParam,zVtx);
+    return;
+  }
+  
+  // Check the track position relatively to the absorber and extrapolate track parameters to the end of the absorber if needed
+  if (trackParam->GetZ() > AliMUONConstants::AbsZBeg()) { // spectro. (z<0)
+    cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Starting Z ("<<trackParam->GetZ()
+        <<") upstream the front absorber (zAbsorberBegin = "<<AliMUONConstants::AbsZBeg()<<")"<<endl;
+    if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,zVtx);
+    else ExtrapToZ(trackParam,zVtx);
+    return;
+  } else if (trackParam->GetZ() > AliMUONConstants::AbsZEnd()) { // spectro. (z<0)
+    cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Starting Z ("<<trackParam->GetZ()
+        <<") inside the front absorber ("<<AliMUONConstants::AbsZBeg()<<","<<AliMUONConstants::AbsZEnd()<<")"<<endl;
+  } else {
+    if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,AliMUONConstants::AbsZEnd());
+    else ExtrapToZ(trackParam,AliMUONConstants::AbsZEnd());
+  }
+  
+  // Get absorber correction parameters assuming linear propagation in absorber
+  Double_t trackXYZOut[3];
+  trackXYZOut[0] = trackParam->GetNonBendingCoor();
+  trackXYZOut[1] = trackParam->GetBendingCoor();
+  trackXYZOut[2] = trackParam->GetZ();
+  Double_t trackXYZIn[3];
+  if (correctForMCS) { // assume linear propagation until the vertex
+    trackXYZIn[2] = TMath::Min(zVtx, AliMUONConstants::AbsZBeg()); // spectro. (z<0)
+    trackXYZIn[0] = trackXYZOut[0] + (xVtx - trackXYZOut[0]) / (zVtx - trackXYZOut[2]) * (trackXYZIn[2] - trackXYZOut[2]);
+    trackXYZIn[1] = trackXYZOut[1] + (yVtx - trackXYZOut[1]) / (zVtx - trackXYZOut[2]) * (trackXYZIn[2] - trackXYZOut[2]);
+  } else {
+    AliMUONTrackParam trackParamIn(*trackParam);
+    ExtrapToZ(&trackParamIn, TMath::Min(zVtx, AliMUONConstants::AbsZBeg()));
+    trackXYZIn[0] = trackParamIn.GetNonBendingCoor();
+    trackXYZIn[1] = trackParamIn.GetBendingCoor();
+    trackXYZIn[2] = trackParamIn.GetZ();
+  }
+  Double_t pTot = trackParam->P();
+  Double_t pathLength, f0, f1, f2, meanRho, totalELoss, sigmaELoss2;
+  if (!GetAbsorberCorrectionParam(trackXYZIn,trackXYZOut,pTot,pathLength,f0,f1,f2,meanRho,totalELoss,sigmaELoss2)) {
+    cout<<"E-AliMUONTrackExtrap::ExtrapToVertex: Unable to take into account the absorber effects"<<endl;
+    if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,zVtx);
+    else ExtrapToZ(trackParam,zVtx);
+    return;
+  }
+  
+  // Compute track parameters and covariances at vertex according to correctForMCS and correctForEnergyLoss flags
+  if (correctForMCS) {
+    
+    if (correctForEnergyLoss) {
+      
+      // Correct for multiple scattering and energy loss
+      CorrectELossEffectInAbsorber(trackParam, 0.5*totalELoss, 0.5*sigmaELoss2);
+      CorrectMCSEffectInAbsorber(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx,
+				 trackXYZIn[2], pathLength, f0, f1, f2);
+      CorrectELossEffectInAbsorber(trackParam, 0.5*totalELoss, 0.5*sigmaELoss2);
+      
+    } else {
+      
+      // Correct for multiple scattering
+      CorrectMCSEffectInAbsorber(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx,
+				 trackXYZIn[2], pathLength, f0, f1, f2);
+    }
+    
+  } else {
+    
+    if (correctForEnergyLoss) {
+      
+      // Correct for energy loss add multiple scattering dispersion in covariance matrix
+      CorrectELossEffectInAbsorber(trackParam, 0.5*totalELoss, 0.5*sigmaELoss2);
+      AddMCSEffectInAbsorber(trackParam, -pathLength, f0, f1, f2); // (spectro. (z<0))
+      ExtrapToZCov(trackParam, trackXYZIn[2]);
+      CorrectELossEffectInAbsorber(trackParam, 0.5*totalELoss, 0.5*sigmaELoss2);
+      ExtrapToZCov(trackParam, zVtx);
+      
+    } else {
+      
+      // add multiple scattering dispersion in covariance matrix
+      AddMCSEffectInAbsorber(trackParam, -pathLength, f0, f1, f2); // (spectro. (z<0))
+      ExtrapToZCov(trackParam, zVtx);
+      
+    }
+    
+  }
+  
 }
 
-
-//  Keep this version for future developments
-  //__________________________________________________________________________
-// void AliMUONTrackExtrap::BransonCorrection(AliMUONTrackParam* trackParam)
-// {
-//   /// Branson correction of track parameters
-//   // the entry parameters have to be calculated at the end of the absorber
-//   Double_t zEndAbsorber, zBP, xBP, yBP;
-//   Double_t  pYZ, pX, pY, pZ, pTotal, xEndAbsorber, yEndAbsorber, radiusEndAbsorber2, pT, theta;
-//   Int_t sign;
-//   // Would it be possible to calculate all that from Geant configuration ????
-//   // and to get the Branson parameters from a function in ABSO module ????
-//   // with an eventual contribution from other detectors like START ????
-//   // Radiation lengths outer part theta > 3 degres
-//   static Double_t x01[9] = { 18.8,    // C (cm)
-// 			     10.397,   // Concrete (cm)
-// 			     0.56,    // Plomb (cm)
-// 			     47.26,   // Polyethylene (cm)
-// 			     0.56,   // Plomb (cm)
-// 			     47.26,   // Polyethylene (cm)
-// 			     0.56,   // Plomb (cm)
-// 			     47.26,   // Polyethylene (cm)
-// 			     0.56 };   // Plomb (cm)
-//   // inner part theta < 3 degres
-//   static Double_t x02[3] = { 18.8,    // C (cm)
-// 			     10.397,   // Concrete (cm)
-// 			     0.35 };    // W (cm) 
-//   // z positions of the materials inside the absober outer part theta > 3 degres
-//   static Double_t z1[10] = { 90, 315, 467, 472, 477, 482, 487, 492, 497, 502 };
-//   // inner part theta < 3 degres
-//   static Double_t z2[4] = { 90, 315, 467, 503 };
-//   static Bool_t first = kTRUE;
-//   static Double_t zBP1, zBP2, rLimit;
-//   // Calculates z positions of the Branson's planes: zBP1 for outer part and zBP2 for inner part (only at the first call)
-//   if (first) {
-//     first = kFALSE;
-//     Double_t aNBP = 0.0;
-//     Double_t aDBP = 0.0;
-//     Int_t iBound;
-//     
-//     for (iBound = 0; iBound < 9; iBound++) {
-//       aNBP = aNBP +
-// 	(z1[iBound+1] * z1[iBound+1] * z1[iBound+1] -
-// 	 z1[iBound]   * z1[iBound]   * z1[iBound]    ) / x01[iBound];
-//       aDBP = aDBP +
-// 	(z1[iBound+1] * z1[iBound+1] - z1[iBound]   * z1[iBound]    ) / x01[iBound];
-//     }
-//     zBP1 = (2.0 * aNBP) / (3.0 * aDBP);
-//     aNBP = 0.0;
-//     aDBP = 0.0;
-//     for (iBound = 0; iBound < 3; iBound++) {
-//       aNBP = aNBP +
-// 	(z2[iBound+1] * z2[iBound+1] * z2[iBound+1] -
-// 	 z2[iBound]   * z2[iBound ]  * z2[iBound]    ) / x02[iBound];
-//       aDBP = aDBP +
-// 	(z2[iBound+1] * z2[iBound+1] - z2[iBound] * z2[iBound]) / x02[iBound];
-//     }
-//     zBP2 = (2.0 * aNBP) / (3.0 * aDBP);
-//     rLimit = z2[3] * TMath::Tan(3.0 * (TMath::Pi()) / 180.);
-//   }
-// 
-//   pYZ = TMath::Abs(1.0 / trackParam->GetInverseBendingMomentum());
-//   sign = 1;      
-//   if (trackParam->GetInverseBendingMomentum() < 0) sign = -1;     
-//   pZ = pYZ / (TMath::Sqrt(1.0 + trackParam->GetBendingSlope() * trackParam->GetBendingSlope())); 
-//   pX = pZ * trackParam->GetNonBendingSlope(); 
-//   pY = pZ * trackParam->GetBendingSlope(); 
-//   pTotal = TMath::Sqrt(pYZ *pYZ + pX * pX);
-//   xEndAbsorber = trackParam->GetNonBendingCoor(); 
-//   yEndAbsorber = trackParam->GetBendingCoor(); 
-//   radiusEndAbsorber2 = xEndAbsorber * xEndAbsorber + yEndAbsorber * yEndAbsorber;
-// 
-//   if (radiusEndAbsorber2 > rLimit*rLimit) {
-//     zEndAbsorber = z1[9];
-//     zBP = zBP1;
-//   } else {
-//     zEndAbsorber = z2[3];
-//     zBP = zBP2;
-//   }
-// 
-//   xBP = xEndAbsorber - (pX / pZ) * (zEndAbsorber - zBP);
-//   yBP = yEndAbsorber - (pY / pZ) * (zEndAbsorber - zBP);
-// 
-//   // new parameters after Branson and energy loss corrections
-//   pZ = pTotal * zBP / TMath::Sqrt(xBP * xBP + yBP * yBP + zBP * zBP);
-//   pX = pZ * xBP / zBP;
-//   pY = pZ * yBP / zBP;
-//   trackParam->SetBendingSlope(pY/pZ);
-//   trackParam->SetNonBendingSlope(pX/pZ);
-//   
-//   pT = TMath::Sqrt(pX * pX + pY * pY);      
-//   theta = TMath::ATan2(pT, pZ); 
-//   pTotal = TotalMomentumEnergyLoss(rLimit, pTotal, theta, xEndAbsorber, yEndAbsorber);
-// 
-//   trackParam->SetInverseBendingMomentum((sign / pTotal) *
-//     TMath::Sqrt(1.0 +
-// 		trackParam->GetBendingSlope() * trackParam->GetBendingSlope() +
-// 		trackParam->GetNonBendingSlope() * trackParam->GetNonBendingSlope()) /
-//     TMath::Sqrt(1.0 + trackParam->GetBendingSlope() * trackParam->GetBendingSlope()));
-// 
-//   // vertex position at (0,0,0)
-//   // should be taken from vertex measurement ???
-//   trackParam->SetBendingCoor(0.);
-//   trackParam->SetNonBendingCoor(0.);
-//   trackParam->SetZ(0.);
-// }
-
-void AliMUONTrackExtrap::BransonCorrection(AliMUONTrackParam* trackParam, Double_t xVtx, Double_t yVtx, Double_t zVtx)
+//__________________________________________________________________________
+void AliMUONTrackExtrap::ExtrapToVertex(AliMUONTrackParam* trackParam,
+					Double_t xVtx, Double_t yVtx, Double_t zVtx,
+					Double_t errXVtx, Double_t errYVtx)
 {
-  /// Branson correction of track parameters
-  // the entry parameters have to be calculated at the end of the absorber
-  // simplified version: the z positions of Branson's planes are no longer calculated
-  // but are given as inputs. One can use the macros MUONTestAbso.C and DrawTestAbso.C
-  // to test this correction. 
-  // Would it be possible to calculate all that from Geant configuration ????
-  // and to get the Branson parameters from a function in ABSO module ????
-  // with an eventual contribution from other detectors like START ????
-  // change to take into account the vertex postition (real, reconstruct,....)
-
-  Double_t  zBP, xBP, yBP;
-  Double_t  pYZ, pX, pY, pZ, pTotal, xEndAbsorber, yEndAbsorber, radiusEndAbsorber2, pT, theta;
-  Int_t sign;
-  static Bool_t first = kTRUE;
-  static Double_t zBP1, zBP2, rLimit, thetaLimit;
-  // zBP1 for outer part and zBP2 for inner part (only at the first call)
-  if (first) {
-    first = kFALSE;
-  
-    thetaLimit = 3.0 * (TMath::Pi()) / 180.;
-    rLimit = TMath::Abs(AliMUONConstants::ZAbsorberEnd()) * TMath::Tan(thetaLimit);
-    zBP1 = -450; // values close to those calculated with EvalAbso.C
-    zBP2 = -480;
-  }
+  /// Extrapolate track parameters to vertex, corrected for multiple scattering and energy loss effects
+  /// Add branson correction resolution and energy loss fluctuation to parameter covariances
+  ExtrapToVertex(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx, kTRUE, kTRUE);
+}
 
-  pYZ = TMath::Abs(1.0 / trackParam->GetInverseBendingMomentum());
-  sign = 1;      
-  if (trackParam->GetInverseBendingMomentum() < 0) sign = -1;  
-  pZ = trackParam->Pz();
-  pX = trackParam->Px(); 
-  pY = trackParam->Py(); 
-  pTotal = TMath::Sqrt(pYZ *pYZ + pX * pX);
-  xEndAbsorber = trackParam->GetNonBendingCoor(); 
-  yEndAbsorber = trackParam->GetBendingCoor(); 
-  radiusEndAbsorber2 = xEndAbsorber * xEndAbsorber + yEndAbsorber * yEndAbsorber;
-
-  if (radiusEndAbsorber2 > rLimit*rLimit) {
-    zBP = zBP1;
-  } else {
-    zBP = zBP2;
-  }
+//__________________________________________________________________________
+void AliMUONTrackExtrap::ExtrapToVertexWithoutELoss(AliMUONTrackParam* trackParam,
+						    Double_t xVtx, Double_t yVtx, Double_t zVtx,
+						    Double_t errXVtx, Double_t errYVtx)
+{
+  /// Extrapolate track parameters to vertex, corrected for multiple scattering effects only
+  /// Add branson correction resolution to parameter covariances
+  ExtrapToVertex(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx, kTRUE, kFALSE);
+}
 
-  xBP = xEndAbsorber - (pX / pZ) * (AliMUONConstants::ZAbsorberEnd() - zBP);
-  yBP = yEndAbsorber - (pY / pZ) * (AliMUONConstants::ZAbsorberEnd() - zBP);
+//__________________________________________________________________________
+void AliMUONTrackExtrap::ExtrapToVertexWithoutBranson(AliMUONTrackParam* trackParam, Double_t zVtx)
+{
+  /// Extrapolate track parameters to vertex, corrected for energy loss effects only
+  /// Add dispersion due to multiple scattering and energy loss fluctuation to parameter covariances
+  ExtrapToVertex(trackParam, 0., 0., zVtx, 0., 0., kFALSE, kTRUE);
+}
 
-  // new parameters after Branson and energy loss corrections
-//   Float_t zSmear = zBP - gRandom->Gaus(0.,2.);  // !!! possible smearing of Z vertex position
+//__________________________________________________________________________
+void AliMUONTrackExtrap::ExtrapToVertexUncorrected(AliMUONTrackParam* trackParam, Double_t zVtx)
+{
+  /// Extrapolate track parameters to vertex without multiple scattering and energy loss corrections
+  /// Add dispersion due to multiple scattering to parameter covariances
+  ExtrapToVertex(trackParam, 0., 0., zVtx, 0., 0., kFALSE, kFALSE);
+}
 
-  Float_t zSmear = zBP ;
+//__________________________________________________________________________
+Double_t AliMUONTrackExtrap::TotalMomentumEnergyLoss(AliMUONTrackParam* trackParam, Double_t xVtx, Double_t yVtx, Double_t zVtx)
+{
+  /// Calculate the total momentum energy loss in-between the track position and the vertex assuming a linear propagation
   
-  pZ = pTotal * (zSmear-zVtx) / TMath::Sqrt((xBP-xVtx) * (xBP-xVtx) + (yBP-yVtx) * (yBP-yVtx) +( zSmear-zVtx) * (zSmear-zVtx) );
-  pX = pZ * (xBP - xVtx)/ (zSmear-zVtx);
-  pY = pZ * (yBP - yVtx) / (zSmear-zVtx);
-  trackParam->SetBendingSlope(pY/pZ);
-  trackParam->SetNonBendingSlope(pX/pZ);
-
+  if (trackParam->GetZ() == zVtx) return 0.; // nothing to be done if already at vertex
   
-  pT = TMath::Sqrt(pX * pX + pY * pY);      
-  theta = TMath::ATan2(pT, TMath::Abs(pZ)); 
-  pTotal = TotalMomentumEnergyLoss(thetaLimit, pTotal, theta);
-
-  trackParam->SetInverseBendingMomentum((sign / pTotal) *
-    TMath::Sqrt(1.0 +
-		trackParam->GetBendingSlope() * trackParam->GetBendingSlope() +
-		trackParam->GetNonBendingSlope() * trackParam->GetNonBendingSlope()) /
-    TMath::Sqrt(1.0 + trackParam->GetBendingSlope() * trackParam->GetBendingSlope()));
-
-  // vertex position at (0,0,0)
-  // should be taken from vertex measurement ???
+  // Check whether the geometry is available
+  if (!gGeoManager) {
+    cout<<"E-AliMUONTrackExtrap::TotalMomentumEnergyLoss: no TGeo"<<endl;
+    return 0.;
+  }
+  
+  // Get encountered material correction parameters assuming linear propagation from vertex to the track position
+  Double_t trackXYZOut[3];
+  trackXYZOut[0] = trackParam->GetNonBendingCoor();
+  trackXYZOut[1] = trackParam->GetBendingCoor();
+  trackXYZOut[2] = trackParam->GetZ();
+  Double_t trackXYZIn[3];
+  trackXYZIn[0] = xVtx;
+  trackXYZIn[1] = yVtx;
+  trackXYZIn[2] = zVtx;
+  Double_t pTot = trackParam->P();
+  Double_t pathLength, f0, f1, f2, meanRho, totalELoss, sigmaELoss2;
+  GetAbsorberCorrectionParam(trackXYZIn,trackXYZOut,pTot,pathLength,f0,f1,f2,meanRho,totalELoss,sigmaELoss2);
+  
+  // total momentum corrected for energy loss
+  Double_t muMass = TDatabasePDG::Instance()->GetParticle("mu-")->Mass(); // GeV
+  Double_t e = TMath::Sqrt(pTot*pTot + muMass*muMass);
+  Double_t eCorr = e + totalELoss;
+  Double_t pTotCorr = TMath::Sqrt(eCorr*eCorr - muMass*muMass);
+  
+  return pTotCorr - pTot;
+}
 
-  trackParam->SetBendingCoor(xVtx);
-  trackParam->SetNonBendingCoor(yVtx);
-  trackParam->SetZ(zVtx);
+//__________________________________________________________________________
+Double_t AliMUONTrackExtrap::BetheBloch(Double_t pTotal, Double_t pathLength, Double_t rho, Double_t atomicZ, Double_t atomicZoverA)
+{
+  /// Returns the mean total momentum energy loss of muon with total momentum='pTotal'
+  /// in the absorber layer of lenght='pathLength', density='rho', A='atomicA' and Z='atomicZ'
+  Double_t muMass = TDatabasePDG::Instance()->GetParticle("mu-")->Mass(); // GeV
+  
+  // mean exitation energy (GeV)
+  Double_t i;
+  if (atomicZ < 13) i = (12. * atomicZ + 7.) * 1.e-9;
+  else i = (9.76 * atomicZ + 58.8 * TMath::Power(atomicZ,-0.19)) * 1.e-9;
+  
+  return pathLength * rho * AliExternalTrackParam::BetheBlochGeant(pTotal/muMass, rho, 0.20, 3.00, i, atomicZoverA);
+}
 
+//__________________________________________________________________________
+Double_t AliMUONTrackExtrap::EnergyLossFluctuation2(Double_t pTotal, Double_t pathLength, Double_t rho, Double_t atomicZoverA)
+{
+  /// Returns the total momentum energy loss fluctuation of muon with total momentum='pTotal'
+  /// in the absorber layer of lenght='pathLength', density='rho', A='atomicA' and Z='atomicZ'
+  Double_t muMass = TDatabasePDG::Instance()->GetParticle("mu-")->Mass(); // GeV
+  //Double_t eMass = 0.510998918e-3; // GeV
+  Double_t k = 0.307075e-3; // GeV.g^-1.cm^2
+  Double_t p2=pTotal*pTotal;
+  Double_t beta2=p2/(p2 + muMass*muMass);
+  
+  Double_t fwhm = 2. * k * rho * pathLength * atomicZoverA / beta2; // FWHM of the energy loss Landau distribution
+  Double_t sigma2 = fwhm * fwhm / (8.*log(2.)); // gaussian: fwmh = 2 * srqt(2*ln(2)) * sigma (i.e. fwmh = 2.35 * sigma)
+  
+  //sigma2 = k * rho * pathLength * atomicZ / atomicA * eMass; // sigma2 of the energy loss gaussian distribution
+  
+  return sigma2;
 }
 
-  //__________________________________________________________________________
-Double_t AliMUONTrackExtrap::TotalMomentumEnergyLoss(Double_t thetaLimit, Double_t pTotal, Double_t theta)
+//__________________________________________________________________________
+void AliMUONTrackExtrap::Cov2CovP(const TMatrixD &param, TMatrixD &cov)
 {
-  /// Returns the total momentum corrected from energy loss in the front absorber
-  // One can use the macros MUONTestAbso.C and DrawTestAbso.C
-  // to test this correction. 
-  // Momentum energy loss behaviour evaluated with the simulation of single muons (april 2002)
-  Double_t deltaP, pTotalCorrected;
-
-   // Parametrization to be redone according to change of absorber material ????
-  // See remark in function BransonCorrection !!!!
-  // The name is not so good, and there are many arguments !!!!
-  if (theta  < thetaLimit ) {
-    if (pTotal < 20) {
-      deltaP = 2.5938 + 0.0570 * pTotal - 0.001151 * pTotal * pTotal;
-    } else {
-      deltaP = 3.0714 + 0.011767 *pTotal;
-    }
-    deltaP *= 0.75; // AZ
-  } else {
-    if (pTotal < 20) {
-      deltaP  = 2.1207 + 0.05478 * pTotal - 0.00145079 * pTotal * pTotal;
-    } else { 
-      deltaP = 2.6069 + 0.0051705 * pTotal;
-    }
-    deltaP *= 0.9; // AZ
-  }
-  pTotalCorrected = pTotal + deltaP / TMath::Cos(theta);
-  return pTotalCorrected;
+  /// change coordinate system: (X, SlopeX, Y, SlopeY, q/Pyz) -> (X, SlopeX, Y, SlopeY, q*PTot)
+  /// parameters (param) are given in the (X, SlopeX, Y, SlopeY, q/Pyz) coordinate system
+  
+  // charge * total momentum
+  Double_t qPTot = TMath::Sqrt(1. + param(1,0)*param(1,0) + param(3,0)*param(3,0)) /
+                   TMath::Sqrt(1. + param(3,0)*param(3,0)) / param(4,0);
+  
+  // Jacobian of the opposite transformation
+  TMatrixD jacob(5,5);
+  jacob.UnitMatrix();
+  jacob(4,1) = qPTot * param(1,0) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
+  jacob(4,3) = - qPTot * param(1,0) * param(1,0) * param(3,0) /
+                 (1. + param(3,0)*param(3,0)) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
+  jacob(4,4) = - qPTot / param(4,0);
+  
+  // compute covariances in new coordinate system
+  TMatrixD tmp(cov,TMatrixD::kMultTranspose,jacob);
+  cov.Mult(jacob,tmp);
 }
 
-  //__________________________________________________________________________
-void AliMUONTrackExtrap::FieldCorrection(AliMUONTrackParam *trackParam, Double_t zEnd)
+//__________________________________________________________________________
+void AliMUONTrackExtrap::CovP2Cov(const TMatrixD &param, TMatrixD &covP)
 {
-  /// Correction of the effect of the magnetic field in the absorber
-  // Assume a constant field along Z axis.
-  Float_t b[3],x[3]; 
-  Double_t bZ;
-  Double_t pYZ,pX,pY,pZ,pT;
-  Double_t pXNew,pYNew;
-  Double_t c;
-
-  pYZ = TMath::Abs(1.0 / trackParam->GetInverseBendingMomentum());
-  c = TMath::Sign(1.0,trackParam->GetInverseBendingMomentum()); // particle charge 
- 
-  pZ = trackParam->Pz();
-  pX = trackParam->Px(); 
-  pY = trackParam->Py();
-  pT = TMath::Sqrt(pX*pX+pY*pY);
-
-  if (TMath::Abs(pZ) <= 0) return;
-  x[2] = zEnd/2;
-  x[0] = x[2]*trackParam->GetNonBendingSlope();  
-  x[1] = x[2]*trackParam->GetBendingSlope();
-
-  // Take magn. field value at position x.
-  if (fgkField) fgkField->Field(x,b);
-  else {
-    cout<<"F-AliMUONTrackExtrap::FieldCorrection: fgkField = 0x0"<<endl;
-    exit(-1);
-  }
-  bZ =  b[2];
- 
-  // Transverse momentum rotation
-  // Parameterized with the study of DeltaPhi = phiReco - phiGen as a function of pZ.
-  Double_t phiShift = c*0.436*0.0003*bZ*zEnd/pZ; 
- // Rotate momentum around Z axis.
-  pXNew = pX*TMath::Cos(phiShift) - pY*TMath::Sin(phiShift);
-  pYNew = pX*TMath::Sin(phiShift) + pY*TMath::Cos(phiShift);
- 
-  trackParam->SetBendingSlope(pYNew/pZ);
-  trackParam->SetNonBendingSlope(pXNew/pZ);
+  /// change coordinate system: (X, SlopeX, Y, SlopeY, q*PTot) -> (X, SlopeX, Y, SlopeY, q/Pyz)
+  /// parameters (param) are given in the (X, SlopeX, Y, SlopeY, q/Pyz) coordinate system
   
-  trackParam->SetInverseBendingMomentum(c/TMath::Sqrt(pYNew*pYNew+pZ*pZ));
- 
+  // charge * total momentum
+  Double_t qPTot = TMath::Sqrt(1. + param(1,0)*param(1,0) + param(3,0)*param(3,0)) /
+                   TMath::Sqrt(1. + param(3,0)*param(3,0)) / param(4,0);
+  
+  // Jacobian of the transformation
+  TMatrixD jacob(5,5);
+  jacob.UnitMatrix();
+  jacob(4,1) = param(4,0) * param(1,0) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
+  jacob(4,3) = - param(4,0) * param(1,0) * param(1,0) * param(3,0) /
+                 (1. + param(3,0)*param(3,0)) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
+  jacob(4,4) = - param(4,0) / qPTot;
+  
+  // compute covariances in new coordinate system
+  TMatrixD tmp(covP,TMatrixD::kMultTranspose,jacob);
+  covP.Mult(jacob,tmp);
 }
 
  //__________________________________________________________________________
-void AliMUONTrackExtrap::ExtrapOneStepHelix(Double_t charge, Double_t step, Double_t *vect, Double_t *vout)
+void AliMUONTrackExtrap::ExtrapOneStepHelix(Double_t charge, Double_t step, const Double_t *vect, Double_t *vout)
 {
+/// <pre>
 ///    ******************************************************************
 ///    *                                                                *
 ///    *  Performs the tracking of one step in a magnetic field         *
@@ -720,12 +1042,13 @@ void AliMUONTrackExtrap::ExtrapOneStepHelix(Double_t charge, Double_t step, Doub
 ///    *   output                                                       *
 ///    *     VOUT = same as VECT after completion of the step           *
 ///    *                                                                *
-///    *    ==>Called by : <USER>, GUSWIM                               *
+///    *    ==>Called by : USER, GUSWIM                               *
 ///    *       Author    m.hansroul  *********                          *
 ///    *       modified  s.egli, s.v.levonian                           *
 ///    *       modified  v.perevoztchikov
 ///    *                                                                *
 ///    ******************************************************************
+/// </pre>
 
 // modif: everything in double precision
 
@@ -761,7 +1084,7 @@ void AliMUONTrackExtrap::ExtrapOneStepHelix(Double_t charge, Double_t step, Doub
     xyz[2]    = vect[kiz] + 0.5 * step * vect[kipz];
 
     //cmodif: call gufld (xyz, h) changed into:
-    GetField (xyz, h);
+    TGeoGlobalMagField::Instance()->Field(xyz,h);
  
     h2xy = h[0]*h[0] + h[1]*h[1];
     h[3] = h[2]*h[2]+ h2xy;
@@ -822,8 +1145,9 @@ void AliMUONTrackExtrap::ExtrapOneStepHelix(Double_t charge, Double_t step, Doub
 }
 
  //__________________________________________________________________________
-void AliMUONTrackExtrap::ExtrapOneStepHelix3(Double_t field, Double_t step, Double_t *vect, Double_t *vout)
+void AliMUONTrackExtrap::ExtrapOneStepHelix3(Double_t field, Double_t step, const Double_t *vect, Double_t *vout)
 {
+/// <pre>
 ///	******************************************************************
 ///	*								 *
 ///	*	Tracking routine in a constant field oriented		 *
@@ -831,11 +1155,12 @@ void AliMUONTrackExtrap::ExtrapOneStepHelix3(Double_t field, Double_t step, Doub
 ///	*	Tracking is performed with a conventional		 *
 ///	*	helix step method					 *
 ///	*								 *
-///	*    ==>Called by : <USER>, GUSWIM				 *
+///	*    ==>Called by : USER, GUSWIM				 *
 ///	*	Authors    R.Brun, M.Hansroul  *********		 *
 ///	*	Rewritten  V.Perevoztchikov
 ///	*								 *
 ///	******************************************************************
+/// </pre>
 
     Double_t hxp[3];
     Double_t h4, hp, rho, tet;
@@ -896,9 +1221,11 @@ void AliMUONTrackExtrap::ExtrapOneStepHelix3(Double_t field, Double_t step, Doub
 
     return;
 }
+
  //__________________________________________________________________________
-void AliMUONTrackExtrap::ExtrapOneStepRungekutta(Double_t charge, Double_t step, Double_t* vect, Double_t* vout)
+Bool_t AliMUONTrackExtrap::ExtrapOneStepRungekutta(Double_t charge, Double_t step, const Double_t* vect, Double_t* vout)
 {
+/// <pre>
 ///	******************************************************************
 ///	*								 *
 ///	*  Runge-Kutta method for tracking a particle through a magnetic *
@@ -914,15 +1241,17 @@ void AliMUONTrackExtrap::ExtrapOneStepRungekutta(Double_t charge, Double_t step,
 ///	*  User routine called  					 *
 ///	*	CALL GUFLD(X,F) 					 *
 ///	*								 *
-///	*    ==>Called by : <USER>, GUSWIM				 *
+///	*    ==>Called by : USER, GUSWIM				 *
 ///	*	Authors    R.Brun, M.Hansroul  *********		 *
 ///	*		   V.Perevoztchikov (CUT STEP implementation)	 *
 ///	*								 *
 ///	*								 *
 ///	******************************************************************
+/// </pre>
 
     Double_t h2, h4, f[4];
-    Double_t xyzt[3], a, b, c, ph,ph2;
+    Double_t xyzt[3] = {FLT_MAX, FLT_MAX, FLT_MAX};
+    Double_t a, b, c, ph,ph2;
     Double_t secxs[4],secys[4],seczs[4],hxp[3];
     Double_t g1, g2, g3, g4, g5, g6, ang2, dxt, dyt, dzt;
     Double_t est, at, bt, ct, cba;
@@ -973,8 +1302,7 @@ void AliMUONTrackExtrap::ExtrapOneStepRungekutta(Double_t charge, Double_t step,
       rest  = step - tl;
       if (TMath::Abs(h) > TMath::Abs(rest)) h = rest;
       //cmodif: call gufld(vout,f) changed into:
-
-      GetField(vout,f);
+      TGeoGlobalMagField::Instance()->Field(vout,f);
 
       // *
       // *             start of integration
@@ -1018,7 +1346,7 @@ void AliMUONTrackExtrap::ExtrapOneStepRungekutta(Double_t charge, Double_t step,
       xyzt[2] = zt;
 
       //cmodif: call gufld(xyzt,f) changed into:
-      GetField(xyzt,f);
+      TGeoGlobalMagField::Instance()->Field(xyzt,f);
 
       at     = a + secxs[0];
       bt     = b + secys[0];
@@ -1055,7 +1383,7 @@ void AliMUONTrackExtrap::ExtrapOneStepRungekutta(Double_t charge, Double_t step,
       xyzt[2] = zt;
 
       //cmodif: call gufld(xyzt,f) changed into:
-      GetField(xyzt,f);
+      TGeoGlobalMagField::Instance()->Field(xyzt,f);
 
       z      = z + (c + (seczs[0] + seczs[1] + seczs[2]) * kthird) * h;
       y      = y + (b + (secys[0] + secys[1] + secys[2]) * kthird) * h;
@@ -1094,16 +1422,22 @@ void AliMUONTrackExtrap::ExtrapOneStepRungekutta(Double_t charge, Double_t step,
       vout[5] = cba*c;
       rest = step - tl;
       if (step < 0.) rest = -rest;
-      if (rest < 1.e-5*TMath::Abs(step)) return;
+      if (rest < 1.e-5*TMath::Abs(step)) return kTRUE;
 
     } while(1);
 
     // angle too big, use helix
+    cout<<"W-AliMUONTrackExtrap::ExtrapOneStepRungekutta: Ruge-Kutta failed: switch to helix"<<endl;
 
     f1  = f[0];
     f2  = f[1];
     f3  = f[2];
     f4  = TMath::Sqrt(f1*f1+f2*f2+f3*f3);
+    if (f4 < 1.e-10) {
+      cout<<"E-AliMUONTrackExtrap::ExtrapOneStepRungekutta: magnetic field at (";
+      cout<<xyzt[0]<<", "<<xyzt[1]<<", "<<xyzt[2]<<") = "<<f4<<": giving up"<<endl;
+      return kFALSE;
+    }
     rho = -f4*pinv;
     tet = rho * step;
  
@@ -1137,24 +1471,6 @@ void AliMUONTrackExtrap::ExtrapOneStepRungekutta(Double_t charge, Double_t step,
     vout[kipy] = vect[kipy] + g4*vect[kipy] + g5*hxp[1] + g6*f2;
     vout[kipz] = vect[kipz] + g4*vect[kipz] + g5*hxp[2] + g6*f3;
 
-    return;
-}
-//___________________________________________________________
- void  AliMUONTrackExtrap::GetField(Double_t *Position, Double_t *Field)
-{
-  /// interface for arguments in double precision (Why ? ChF)
-  Float_t x[3], b[3];
-
-  x[0] = Position[0]; x[1] = Position[1]; x[2] = Position[2];
-
-  if (fgkField) fgkField->Field(x,b);
-  else {
-    cout<<"F-AliMUONTrackExtrap::GetField: fgkField = 0x0"<<endl;
-    exit(-1);
-  }
-  
-  Field[0] = b[0]; Field[1] = b[1]; Field[2] = b[2];
-
-  return;
+    return kTRUE;
 }