Fixed calculation of fluctuations of energy loss in absrber.

(Philippe P.)

diff --git a/MUON/AliMUONTrackExtrap.cxx b/MUON/AliMUONTrackExtrap.cxx
index 72e9b3aeccd87f2d69ce40c8eb32042acdfdcf89..45dcc35c0c02e311e4bd3aba9bec84d1b19baf5f 100644 (file)
--- a/MUON/AliMUONTrackExtrap.cxx
+++ b/MUON/AliMUONTrackExtrap.cxx
@@ -616,6 +616,7 @@ Bool_t AliMUONTrackExtrap::GetAbsorberCorrectionParam(Double_t trackXYZIn[3], Do
   Double_t atomicZoverA = 0.; // Z/A of material
   Double_t localPathLength = 0;
   Double_t remainingPathLength = pathLength;
+  Double_t sigmaELoss = 0.;
   Double_t zB = trackXYZIn[2];
   Double_t zE, dzB, dzE;
   do {
@@ -671,7 +672,7 @@ Bool_t AliMUONTrackExtrap::GetAbsorberCorrectionParam(Double_t trackXYZIn[3], Do
     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);
+    sigmaELoss += EnergyLossFluctuation(pTotal, localPathLength, rho, atomicZoverA);
     
     // prepare next step
     zB = zE;
@@ -679,6 +680,7 @@ Bool_t AliMUONTrackExtrap::GetAbsorberCorrectionParam(Double_t trackXYZIn[3], Do
   } while (remainingPathLength > TGeoShape::Tolerance());
   
   meanRho /= pathLength;
+  sigmaELoss2 = sigmaELoss*sigmaELoss;
   
   return kTRUE;
 }
@@ -963,7 +965,7 @@ Double_t AliMUONTrackExtrap::BetheBloch(Double_t pTotal, Double_t pathLength, Do
 }
 
 //__________________________________________________________________________
-Double_t AliMUONTrackExtrap::EnergyLossFluctuation2(Double_t pTotal, Double_t pathLength, Double_t rho, Double_t atomicZoverA)
+Double_t AliMUONTrackExtrap::EnergyLossFluctuation(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'
@@ -974,11 +976,11 @@ Double_t AliMUONTrackExtrap::EnergyLossFluctuation2(Double_t pTotal, Double_t pa
   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)
+  Double_t sigma = fwhm / TMath::Sqrt(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;
+  return sigma;
 }
 
 //__________________________________________________________________________

diff --git a/MUON/AliMUONTrackExtrap.h b/MUON/AliMUONTrackExtrap.h
index 809c4692a3f7b45518a8616dacec7a57006d18fa..0648468f296e902e77561e32f0773fcf21ad23be 100644 (file)
--- a/MUON/AliMUONTrackExtrap.h
+++ b/MUON/AliMUONTrackExtrap.h
@@ -115,7 +115,7 @@ class AliMUONTrackExtrap : public TObject
                                            Double_t &meanRho, Double_t &totalELoss, Double_t &sigmaELoss2);
   
   static Double_t BetheBloch(Double_t pTotal, Double_t pathLength, Double_t rho, Double_t atomicZ, Double_t atomicZoverA);
-  static Double_t EnergyLossFluctuation2(Double_t pTotal, Double_t pathLength, Double_t rho, Double_t atomicZoverA);
+  static Double_t EnergyLossFluctuation(Double_t pTotal, Double_t pathLength, Double_t rho, Double_t atomicZoverA);
   
   static void Cov2CovP(const TMatrixD &param, TMatrixD &cov);
   static void CovP2Cov(const TMatrixD &param, TMatrixD &cov);