* provided "as is" without express or implied warranty. *
**************************************************************************/
-/*
-$Log$
-Revision 1.1.2.3 2000/06/09 21:03:09 morsch
-Make includes consistent with new file structure.
+/* $Id$ */
-Revision 1.1.2.2 2000/06/09 12:58:05 gosset
-Removed comment beginnings in Log sections of .cxx files
-Suppressed most violations of coding rules
-
-Revision 1.1.2.1 2000/06/07 14:44:53 gosset
-Addition of files for track reconstruction in C++
-*/
-
-//__________________________________________________________________________
+///////////////////////////////////////////////////
//
-// Track parameters in ALICE dimuon spectrometer
-//__________________________________________________________________________
+// Track parameters
+// in
+// ALICE
+// dimuon
+// spectrometer
+//
+///////////////////////////////////////////////////
-#include <iostream.h>
+#include <Riostream.h>
#include "AliCallf77.h"
-#include "AliMUON.h"
-#include "AliMUONHitForRec.h"
-#include "AliMUONSegment.h"
+#include "AliMUON.h"
#include "AliMUONTrackParam.h"
-#include "AliMUONChamber.h"
+#include "AliMUONChamber.h"
#include "AliRun.h"
+#include "AliMagF.h"
ClassImp(AliMUONTrackParam) // Class implementation in ROOT context
+ // A few calls in Fortran or from Fortran (extrap.F).
+ // Needed, instead of calls to Geant subroutines,
+ // because double precision is necessary for track fit converging with Minuit.
+ // The "extrap" functions should be translated into C++ ????
#ifndef WIN32
-# define reco_ghelix reco_ghelix_
+# define extrap_onestep_helix extrap_onestep_helix_
+# define extrap_onestep_helix3 extrap_onestep_helix3_
+# define extrap_onestep_rungekutta extrap_onestep_rungekutta_
+# define gufld_double gufld_double_
#else
-# define reco_ghelix RECO_GHELIX
+# define extrap_onestep_helix EXTRAP_ONESTEP_HELIX
+# define extrap_onestep_helix3 EXTRAP_ONESTEP_HELIX3
+# define extrap_onestep_rungekutta EXTRAP_ONESTEP_RUNGEKUTTA
+# define gufld_double GUFLD_DOUBLE
#endif
-extern "C"
-{
-void type_of_call reco_ghelix(Double_t &Charge, Double_t &StepLength, Double_t *VGeant3, Double_t *VGeant3New);
+extern "C" {
+ void type_of_call extrap_onestep_helix
+ (Double_t &Charge, Double_t &StepLength, Double_t *VGeant3, Double_t *VGeant3New);
+
+ void type_of_call extrap_onestep_helix3
+ (Double_t &Field, Double_t &StepLength, Double_t *VGeant3, Double_t *VGeant3New);
+
+ void type_of_call extrap_onestep_rungekutta
+ (Double_t &Charge, Double_t &StepLength, Double_t *VGeant3, Double_t *VGeant3New);
+
+ void type_of_call gufld_double(Double_t *Position, Double_t *Field) {
+ // interface to "gAlice->Field()->Field" for arguments in double precision
+ Float_t x[3], b[3];
+ x[0] = Position[0]; x[1] = Position[1]; x[2] = Position[2];
+ gAlice->Field()->Field(x, b);
+ Field[0] = b[0]; Field[1] = b[1]; Field[2] = b[2];
+ }
}
+ //_________________________________________________________________________
+
+AliMUONTrackParam& AliMUONTrackParam::operator=(const AliMUONTrackParam& MUONTrackParam)
+{
+ if (this == &MUONTrackParam)
+ return *this;
-// Inline functions for Get and Set: inline removed because it does not work !!!!
-Double_t AliMUONTrackParam::GetInverseBendingMomentum(void) {
- // Get fInverseBendingMomentum
- return fInverseBendingMomentum;}
-void AliMUONTrackParam::SetInverseBendingMomentum(Double_t InverseBendingMomentum) {
- // Set fInverseBendingMomentum
- fInverseBendingMomentum = InverseBendingMomentum;}
-Double_t AliMUONTrackParam::GetBendingSlope(void) {
- // Get fBendingSlope
- return fBendingSlope;}
-void AliMUONTrackParam::SetBendingSlope(Double_t BendingSlope) {
- // Set fBendingSlope
- fBendingSlope = BendingSlope;}
-Double_t AliMUONTrackParam::GetNonBendingSlope(void) {
- // Get fNonBendingSlope
- return fNonBendingSlope;}
-void AliMUONTrackParam::SetNonBendingSlope(Double_t NonBendingSlope) {
- // Set fNonBendingSlope
- fNonBendingSlope = NonBendingSlope;}
-Double_t AliMUONTrackParam::GetZ(void) {
- // Get fZ
- return fZ;}
-void AliMUONTrackParam::SetZ(Double_t Z) {
- // Set fZ
- fZ = Z;}
-Double_t AliMUONTrackParam::GetBendingCoor(void) {
- // Get fBendingCoor
- return fBendingCoor;}
-void AliMUONTrackParam::SetBendingCoor(Double_t BendingCoor) {
- // Set fBendingCoor
- fBendingCoor = BendingCoor;}
-Double_t AliMUONTrackParam::GetNonBendingCoor(void) {
- // Get fNonBendingCoor
- return fNonBendingCoor;}
-void AliMUONTrackParam::SetNonBendingCoor(Double_t NonBendingCoor) {
- // Set fNonBendingCoor
- fNonBendingCoor = NonBendingCoor;}
+ fInverseBendingMomentum = MUONTrackParam.fInverseBendingMomentum;
+ fBendingSlope = MUONTrackParam.fBendingSlope;
+ fNonBendingSlope = MUONTrackParam.fNonBendingSlope;
+ fZ = MUONTrackParam.fZ;
+ fBendingCoor = MUONTrackParam.fBendingCoor;
+ fNonBendingCoor = MUONTrackParam.fNonBendingCoor;
+
+ return *this;
+}
+ //_________________________________________________________________________
+AliMUONTrackParam::AliMUONTrackParam(const AliMUONTrackParam& MUONTrackParam):TObject(MUONTrackParam)
+{
+ fInverseBendingMomentum = MUONTrackParam.fInverseBendingMomentum;
+ fBendingSlope = MUONTrackParam.fBendingSlope;
+ fNonBendingSlope = MUONTrackParam.fNonBendingSlope;
+ fZ = MUONTrackParam.fZ;
+ fBendingCoor = MUONTrackParam.fBendingCoor;
+ fNonBendingCoor = MUONTrackParam.fNonBendingCoor;
+}
//__________________________________________________________________________
void AliMUONTrackParam::ExtrapToZ(Double_t Z)
// Track parameter extrapolation to the plane at "Z".
// On return, the track parameters resulting from the extrapolation
// replace the current track parameters.
- // Use "reco_ghelix" which should be replaced by something else !!!!
if (this->fZ == Z) return; // nothing to be done if same Z
Double_t forwardBackward; // +1 if forward, -1 if backward
- if (Z > this->fZ) forwardBackward = 1.0;
+ if (Z < this->fZ) forwardBackward = 1.0; // spectro. z<0
else forwardBackward = -1.0;
- Double_t temp, vGeant3[7], vGeant3New[7]; // 7 in parameter ????
+ Double_t vGeant3[7], vGeant3New[7]; // 7 in parameter ????
Int_t iGeant3, stepNumber;
Int_t maxStepNumber = 5000; // in parameter ????
// For safety: return kTRUE or kFALSE ????
- // Parameter vector for calling GHELIX in Geant3
+ // Parameter vector for calling EXTRAP_ONESTEP
SetGeant3Parameters(vGeant3, forwardBackward);
- // For use of reco_ghelix...: invert X and Y, PX/PTOT and PY/PTOT !!!!
- temp = vGeant3[0]; vGeant3[0] = vGeant3[1]; vGeant3[1] = temp;
- temp = vGeant3[3]; vGeant3[3] = vGeant3[4]; vGeant3[4] = temp;
- // charge must be changed with momentum for backward motion
- Double_t charge =
- forwardBackward * TMath::Sign(Double_t(1.0), this->fInverseBendingMomentum);
+ // sign of charge (sign of fInverseBendingMomentum if forward motion)
+ // must be changed if backward extrapolation
+ Double_t chargeExtrap = forwardBackward *
+ TMath::Sign(Double_t(1.0), this->fInverseBendingMomentum);
Double_t stepLength = 6.0; // in parameter ????
// Extrapolation loop
stepNumber = 0;
- while (((forwardBackward * (vGeant3[2] - Z)) <= 0.0) &&
+ while (((-forwardBackward * (vGeant3[2] - Z)) <= 0.0) && // spectro. z<0
(stepNumber < maxStepNumber)) {
stepNumber++;
- // call Geant3 "ghelix" subroutine through a copy in "reco_muon.F":
- // the true function should be called, but how ???? and remove prototyping ...
- reco_ghelix(charge, stepLength, vGeant3, vGeant3New);
- if ((forwardBackward * (vGeant3New[2] - Z)) > 0.0) break; // one is beyond Z
+ // Option for switching between helix and Runge-Kutta ????
+ // extrap_onestep_rungekutta(chargeExtrap, stepLength, vGeant3, vGeant3New);
+ extrap_onestep_helix(chargeExtrap, stepLength, vGeant3, vGeant3New);
+ if ((-forwardBackward * (vGeant3New[2] - Z)) > 0.0) break; // one is beyond Z spectro. z<0
// better use TArray ????
for (iGeant3 = 0; iGeant3 < 7; iGeant3++)
{vGeant3[iGeant3] = vGeant3New[iGeant3];}
}
// check maxStepNumber ????
- // For use of reco_ghelix...:
- // invert back X and Y, PX/PTOT and PY/PTOT, both for vGeant3 and vGeant3New !!!!
- temp = vGeant3[0]; vGeant3[0] = vGeant3[1]; vGeant3[1] = temp;
- temp = vGeant3New[0]; vGeant3New[0] = vGeant3New[1]; vGeant3New[1] = temp;
- temp = vGeant3[3]; vGeant3[3] = vGeant3[4]; vGeant3[4] = temp;
- temp = vGeant3New[3]; vGeant3New[3] = vGeant3New[4]; vGeant3New[4] = temp;
// Interpolation back to exact Z (2nd order)
// should be in function ???? using TArray ????
Double_t dZ12 = vGeant3New[2] - vGeant3[2]; // 1->2
vGeant3[2] = Z; // Z
Double_t xPrimeI = xPrime - 0.5 * xSecond * (dZi2 - dZ1i);
Double_t yPrimeI = yPrime - 0.5 * ySecond * (dZi2 - dZ1i);
+ // (PX, PY, PZ)/PTOT assuming forward motion
vGeant3[5] =
1.0 / TMath::Sqrt(1.0 + xPrimeI * xPrimeI + yPrimeI * yPrimeI); // PZ/PTOT
vGeant3[3] = xPrimeI * vGeant3[5]; // PX/PTOT
vGeant3[4] = yPrimeI * vGeant3[5]; // PY/PTOT
- // Track parameters from Geant3 parameters
- GetFromGeant3Parameters(vGeant3, charge);
+ // Track parameters from Geant3 parameters,
+ // with charge back for forward motion
+ GetFromGeant3Parameters(vGeant3, chargeExtrap * forwardBackward);
}
//__________________________________________________________________________
VGeant3[6] =
TMath::Sqrt(pYZ * pYZ +
pZ * pZ * this->fNonBendingSlope * this->fNonBendingSlope); // PTOT
- VGeant3[5] = ForwardBackward * pZ / VGeant3[6]; // PZ/PTOT
+ VGeant3[5] = -ForwardBackward * pZ / VGeant3[6]; // PZ/PTOT spectro. z<0
VGeant3[3] = this->fNonBendingSlope * VGeant3[5]; // PX/PTOT
VGeant3[4] = this->fBendingSlope * VGeant3[5]; // PY/PTOT
}
void AliMUONTrackParam::GetFromGeant3Parameters(Double_t *VGeant3, Double_t Charge)
{
// Get track parameters in current AliMUONTrackParam
- // from Geant3 parameters pointed to by "VGeant3".
+ // from Geant3 parameters pointed to by "VGeant3",
+ // assumed to be calculated for forward motion in Z.
// "InverseBendingMomentum" is signed with "Charge".
this->fNonBendingCoor = VGeant3[0]; // X
this->fBendingCoor = VGeant3[1]; // Y
// are returned in the array (dimension 2) of track parameters
// pointed to by "TrackParam" (index 0 and 1 for first and second chambers).
Double_t extZ[2], z1, z2;
- Int_t i1, i2;
+ Int_t i1 = -1, i2 = -1; // = -1 to avoid compilation warnings
AliMUON *pMUON = (AliMUON*) gAlice->GetModule("MUON"); // necessary ????
// range of Station to be checked ????
z1 = (&(pMUON->Chamber(2 * Station)))->Z(); // Z of first chamber
return;
}
+ //__________________________________________________________________________
+void AliMUONTrackParam::ExtrapToVertex()
+{
+ // 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
+
+ Double_t zAbsorber = -503.0; // to be coherent with the Geant absorber geometry !!!!
+ // spectro. (z<0)
+ // Extrapolates track parameters upstream to the "Z" end of the front absorber
+ ExtrapToZ(zAbsorber); // !!!
+ // Makes Branson correction (multiple scattering + energy loss)
+ BransonCorrection();
+ // Makes a simple magnetic field correction through the absorber
+ FieldCorrection(zAbsorber);
+}
+
+
+// Keep this version for future developments
+ //__________________________________________________________________________
+// void AliMUONTrackParam::BransonCorrection()
+// {
+// // 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 / fInverseBendingMomentum);
+// sign = 1;
+// if (fInverseBendingMomentum < 0) sign = -1;
+// pZ = pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope));
+// pX = pZ * fNonBendingSlope;
+// pY = pZ * fBendingSlope;
+// pTotal = TMath::Sqrt(pYZ *pYZ + pX * pX);
+// xEndAbsorber = fNonBendingCoor;
+// yEndAbsorber = fBendingCoor;
+// 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;
+// fBendingSlope = pY / pZ;
+// fNonBendingSlope = pX / pZ;
+
+// pT = TMath::Sqrt(pX * pX + pY * pY);
+// theta = TMath::ATan2(pT, pZ);
+// pTotal =
+// TotalMomentumEnergyLoss(rLimit, pTotal, theta, xEndAbsorber, yEndAbsorber);
+
+// fInverseBendingMomentum = (sign / pTotal) *
+// TMath::Sqrt(1.0 +
+// fBendingSlope * fBendingSlope +
+// fNonBendingSlope * fNonBendingSlope) /
+// TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope);
+
+// // vertex position at (0,0,0)
+// // should be taken from vertex measurement ???
+// fBendingCoor = 0.0;
+// fNonBendingCoor = 0;
+// fZ= 0;
+// }
+
+void AliMUONTrackParam::BransonCorrection()
+{
+ // 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 ????
+ 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, zEndAbsorber;
+ // zBP1 for outer part and zBP2 for inner part (only at the first call)
+ if (first) {
+ first = kFALSE;
+
+ zEndAbsorber = -503; // spectro (z<0)
+ thetaLimit = 3.0 * (TMath::Pi()) / 180.;
+ rLimit = TMath::Abs(zEndAbsorber) * TMath::Tan(thetaLimit);
+ zBP1 = -450; // values close to those calculated with EvalAbso.C
+ zBP2 = -480;
+ }
+
+ pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
+ sign = 1;
+ if (fInverseBendingMomentum < 0) sign = -1;
+ pZ = -pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope)); // spectro (z<0)
+ pX = pZ * fNonBendingSlope;
+ pY = pZ * fBendingSlope;
+ pTotal = TMath::Sqrt(pYZ *pYZ + pX * pX);
+ xEndAbsorber = fNonBendingCoor;
+ yEndAbsorber = fBendingCoor;
+ radiusEndAbsorber2 = xEndAbsorber * xEndAbsorber + yEndAbsorber * yEndAbsorber;
+
+ if (radiusEndAbsorber2 > rLimit*rLimit) {
+ zBP = zBP1;
+ } else {
+ zBP = zBP2;
+ }
+
+ xBP = xEndAbsorber - (pX / pZ) * (zEndAbsorber - zBP);
+ yBP = yEndAbsorber - (pY / pZ) * (zEndAbsorber - zBP);
+
+ // new parameters after Branson and energy loss corrections
+// Float_t zSmear = zBP - gRandom->Gaus(0.,2.); // !!! possible smearing of Z vertex position
+ Float_t zSmear = zBP;
+
+ pZ = pTotal * zSmear / TMath::Sqrt(xBP * xBP + yBP * yBP + zSmear * zSmear);
+ pX = pZ * xBP / zSmear;
+ pY = pZ * yBP / zSmear;
+ fBendingSlope = pY / pZ;
+ fNonBendingSlope = pX / pZ;
+
+
+ pT = TMath::Sqrt(pX * pX + pY * pY);
+ theta = TMath::ATan2(pT, TMath::Abs(pZ));
+ pTotal = TotalMomentumEnergyLoss(thetaLimit, pTotal, theta);
+
+ fInverseBendingMomentum = (sign / pTotal) *
+ TMath::Sqrt(1.0 +
+ fBendingSlope * fBendingSlope +
+ fNonBendingSlope * fNonBendingSlope) /
+ TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope);
+
+ // vertex position at (0,0,0)
+ // should be taken from vertex measurement ???
+ fBendingCoor = 0.0;
+ fNonBendingCoor = 0;
+ fZ= 0;
+}
+
+ //__________________________________________________________________________
+Double_t AliMUONTrackParam::TotalMomentumEnergyLoss(Double_t thetaLimit, Double_t pTotal, Double_t theta)
+{
+ // 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;
+ }
+ } else {
+ if (pTotal < 20) {
+ deltaP = 2.1207 + 0.05478 * pTotal - 0.00145079 * pTotal * pTotal;
+ } else {
+ deltaP = 2.6069 + 0.0051705 * pTotal;
+ }
+ }
+ pTotalCorrected = pTotal + deltaP / TMath::Cos(theta);
+ return pTotalCorrected;
+}
+
+ //__________________________________________________________________________
+void AliMUONTrackParam::FieldCorrection(Double_t Z)
+{
+ //
+ // 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 / fInverseBendingMomentum);
+ c = TMath::Sign(1.0,fInverseBendingMomentum); // particle charge
+
+ pZ = -pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope)); // spectro. (z<0)
+ pX = pZ * fNonBendingSlope;
+ pY = pZ * fBendingSlope;
+ pT = TMath::Sqrt(pX*pX+pY*pY);
+
+ if (TMath::Abs(pZ) <= 0) return;
+ x[2] = Z/2;
+ x[0] = x[2]*fNonBendingSlope;
+ x[1] = x[2]*fBendingSlope;
+
+ // Take magn. field value at position x.
+ gAlice->Field()->Field(x, b);
+ 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*Z/pZ;
+ // Rotate momentum around Z axis.
+ pXNew = pX*TMath::Cos(phiShift) - pY*TMath::Sin(phiShift);
+ pYNew = pX*TMath::Sin(phiShift) + pY*TMath::Cos(phiShift);
+
+ fBendingSlope = pYNew / pZ;
+ fNonBendingSlope = pXNew / pZ;
+
+ fInverseBendingMomentum = c / TMath::Sqrt(pYNew*pYNew+pZ*pZ);
+
+}
git://git.uio.no / u / mrichter / AliRoot.git / blobdiff