/*
$Log$
+Revision 1.11.6.1 2002/10/11 06:56:48 hristov
+Updating VirtualMC to v3-09-02
+
+Revision 1.12 2002/09/19 10:14:00 cussonno
+Modified absorber correction. Added function FieldCorrection() to account
+for the effect of magnetic field in absorber.
+
+Revision 1.11 2002/03/08 17:25:36 cussonno
+Update absorber energy loss and Branson corrections : simplified functions
+BransonCorrection and TotalMomentumEnergyLoss.
+
Revision 1.10 2001/04/25 14:50:42 gosset
Corrections to violations of coding conventions
Double_t zAbsorber = 503.0; // to be coherent with the Geant absorber geometry !!!!
// Extrapolates track parameters upstream to the "Z" end of the front absorber
- ExtrapToZ(zAbsorber);
+ ExtrapToZ(zAbsorber); // !!!
// Makes Branson correction (multiple scattering + energy loss)
BransonCorrection();
+ // Makes a simple magnetic field correction through the absorber
+ FieldCorrection(zAbsorber);
}
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, zEndAbsorber;
+ 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;
- rLimit = zEndAbsorber * TMath::Tan(3.0 * (TMath::Pi()) / 180.);
- zBP1 = 450;
+ thetaLimit = 3.0 * (TMath::Pi()) / 180.;
+ rLimit = zEndAbsorber * TMath::Tan(thetaLimit);
+ zBP1 = 450; // values close to those calculated with EvalAbso.C
zBP2 = 480;
}
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;
+// 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, pZ);
- pTotal =
- TotalMomentumEnergyLoss(rLimit, pTotal, theta, xEndAbsorber, yEndAbsorber);
+ pTotal = TotalMomentumEnergyLoss(thetaLimit, pTotal, theta);
fInverseBendingMomentum = (sign / pTotal) *
TMath::Sqrt(1.0 +
fNonBendingCoor = 0;
fZ= 0;
}
+
//__________________________________________________________________________
-Double_t AliMUONTrackParam::TotalMomentumEnergyLoss(Double_t rLimit, Double_t pTotal, Double_t theta, Double_t xEndAbsorber, Double_t yEndAbsorber)
+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;
- Double_t radiusEndAbsorber2 =
- xEndAbsorber *xEndAbsorber + yEndAbsorber * yEndAbsorber;
- // Parametrization to be redone according to change of absorber material ????
+ // 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 (radiusEndAbsorber2 < rLimit * rLimit) {
- if (pTotal < 15) {
- deltaP = 2.737 + 0.0494 * pTotal - 0.001123 * pTotal * pTotal;
+ if (theta < thetaLimit ) {
+ if (pTotal < 20) {
+ deltaP = 2.5938 + 0.0570 * pTotal - 0.001151 * pTotal * pTotal;
} else {
- deltaP = 3.0643 + 0.01346 *pTotal;
+ deltaP = 3.0714 + 0.011767 *pTotal;
}
- deltaP = 0.63 * deltaP; // !!!! changes in the absorber composition ????
} else {
- if (pTotal < 15) {
- deltaP = 2.1380 + 0.0351 * pTotal - 0.000853 * pTotal * pTotal;
+ if (pTotal < 20) {
+ deltaP = 2.1207 + 0.05478 * pTotal - 0.00145079 * pTotal * pTotal;
} else {
- deltaP = 2.407 + 0.00702 * pTotal;
+ deltaP = 2.6069 + 0.0051705 * pTotal;
}
- deltaP = 0.67 * deltaP; // !!!! changes in the absorber composition ????
}
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));
+ pX = pZ * fNonBendingSlope;
+ pY = pZ * fBendingSlope;
+ pT = TMath::Sqrt(pX*pX+pY*pY);
+
+ if (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