/*
$Log$
+Revision 1.2 2000/06/15 07:58:49 morsch
+Code from MUON-dev joined
+
Revision 1.1.2.3 2000/06/09 21:03:09 morsch
Make includes consistent with new file structure.
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 !!!!
+ // Extrapolates track parameters upstream to the "Z" end of the front absorber
+ ExtrapToZ(zAbsorber);
+ // Makes Branson correction (multiple scattering + energy loss)
+ BransonCorrection();
+}
+
+ //__________________________________________________________________________
+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 ????
+ // 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;
+ for (Int_t 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 (Int_t 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[2];
+ 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;
+}
+
+ //__________________________________________________________________________
+Double_t AliMUONTrackParam::TotalMomentumEnergyLoss(Double_t rLimit, Double_t pTotal, Double_t theta, Double_t xEndAbsorber, Double_t yEndAbsorber)
+{
+ // Returns the total momentum corrected from energy loss in the front absorber
+ Double_t deltaP, pTotalCorrected;
+
+ Double_t radiusEndAbsorber2 =
+ xEndAbsorber *xEndAbsorber + yEndAbsorber * yEndAbsorber;
+ // Parametrization to be redone according to change of absorber material ????
+ // 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;
+ } else {
+ deltaP = 3.0643 + 0.01346 *pTotal;
+ }
+ } else {
+ if (pTotal < 15) {
+ deltaP = 2.1380 + 0.0351 * pTotal - 0.000853 * pTotal * pTotal;
+ } else {
+ deltaP = 2.407 + 0.00702 * pTotal;
+ }
+ }
+ pTotalCorrected = pTotal + deltaP / TMath::Cos(theta);
+ return pTotalCorrected;
+}
+
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