1 /**************************************************************************
2 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
7 * Permission to use, copy, modify and distribute this software and its *
8 * documentation strictly for non-commercial purposes is hereby granted *
9 * without fee, provided that the above copyright notice appears in all *
10 * copies and that both the copyright notice and this permission notice *
11 * appear in the supporting documentation. The authors make no claims *
12 * about the suitability of this software for any purpose. It is *
13 * provided "as is" without express or implied warranty. *
14 **************************************************************************/
18 //-----------------------------------------------------------------------------
19 // Class AliMUONTrackExtrap
20 // ------------------------
21 // Tools for track extrapolation in ALICE dimuon spectrometer
22 // Author: Philippe Pillot
23 //-----------------------------------------------------------------------------
25 #include "AliMUONTrackExtrap.h"
26 #include "AliMUONTrackParam.h"
27 #include "AliMUONConstants.h"
28 #include "AliMUONReconstructor.h"
31 #include "AliExternalTrackParam.h"
33 #include <TGeoGlobalMagField.h>
34 #include <TGeoManager.h>
36 #include <TDatabasePDG.h>
38 #include <Riostream.h>
41 ClassImp(AliMUONTrackExtrap) // Class implementation in ROOT context
44 const Double_t AliMUONTrackExtrap::fgkSimpleBPosition = 0.5 * (AliMUONConstants::CoilZ() + AliMUONConstants::YokeZ());
45 const Double_t AliMUONTrackExtrap::fgkSimpleBLength = 0.5 * (AliMUONConstants::CoilL() + AliMUONConstants::YokeL());
46 Double_t AliMUONTrackExtrap::fgSimpleBValue = 0.;
47 Bool_t AliMUONTrackExtrap::fgFieldON = kFALSE;
48 const Bool_t AliMUONTrackExtrap::fgkUseHelix = kFALSE;
49 const Int_t AliMUONTrackExtrap::fgkMaxStepNumber = 5000;
50 const Double_t AliMUONTrackExtrap::fgkHelixStepLength = 6.;
51 const Double_t AliMUONTrackExtrap::fgkRungeKuttaMaxResidue = 0.002;
53 //__________________________________________________________________________
54 void AliMUONTrackExtrap::SetField()
56 /// set field on/off flag;
57 /// set field at the centre of the dipole
58 const Double_t x[3] = {50.,50.,fgkSimpleBPosition};
59 Double_t b[3] = {0.,0.,0.};
60 TGeoGlobalMagField::Instance()->Field(x,b);
61 fgSimpleBValue = b[0];
62 fgFieldON = fgSimpleBValue ? kTRUE : kFALSE;
66 //__________________________________________________________________________
67 Double_t AliMUONTrackExtrap::GetImpactParamFromBendingMomentum(Double_t bendingMomentum)
69 /// Returns impact parameter at vertex in bending plane (cm),
70 /// from the signed bending momentum "BendingMomentum" in bending plane (GeV/c),
71 /// using simple values for dipole magnetic field.
72 /// The sign of "BendingMomentum" is the sign of the charge.
74 if (bendingMomentum == 0.) return 1.e10;
76 const Double_t kCorrectionFactor = 1.1; // impact parameter is 10% underestimated
78 return kCorrectionFactor * (-0.0003 * fgSimpleBValue * fgkSimpleBLength * fgkSimpleBPosition / bendingMomentum);
81 //__________________________________________________________________________
83 AliMUONTrackExtrap::GetBendingMomentumFromImpactParam(Double_t impactParam)
85 /// Returns signed bending momentum in bending plane (GeV/c),
86 /// the sign being the sign of the charge for particles moving forward in Z,
87 /// from the impact parameter "ImpactParam" at vertex in bending plane (cm),
88 /// using simple values for dipole magnetic field.
90 if (impactParam == 0.) return 1.e10;
92 const Double_t kCorrectionFactor = 1.1; // bending momentum is 10% underestimated
96 return kCorrectionFactor * (-0.0003 * fgSimpleBValue * fgkSimpleBLength * fgkSimpleBPosition / impactParam);
100 return AliMUONConstants::GetMostProbBendingMomentum();
104 //__________________________________________________________________________
105 void AliMUONTrackExtrap::LinearExtrapToZ(AliMUONTrackParam* trackParam, Double_t zEnd)
107 /// Track parameters linearly extrapolated to the plane at "zEnd".
108 /// On return, results from the extrapolation are updated in trackParam.
110 if (trackParam->GetZ() == zEnd) return; // nothing to be done if same z
112 // Compute track parameters
113 Double_t dZ = zEnd - trackParam->GetZ();
114 trackParam->SetNonBendingCoor(trackParam->GetNonBendingCoor() + trackParam->GetNonBendingSlope() * dZ);
115 trackParam->SetBendingCoor(trackParam->GetBendingCoor() + trackParam->GetBendingSlope() * dZ);
116 trackParam->SetZ(zEnd);
119 //__________________________________________________________________________
120 void AliMUONTrackExtrap::LinearExtrapToZCov(AliMUONTrackParam* trackParam, Double_t zEnd, Bool_t updatePropagator)
122 /// Track parameters and their covariances linearly extrapolated to the plane at "zEnd".
123 /// On return, results from the extrapolation are updated in trackParam.
125 if (trackParam->GetZ() == zEnd) return; // nothing to be done if same z
127 // No need to propagate the covariance matrix if it does not exist
128 if (!trackParam->CovariancesExist()) {
129 cout<<"W-AliMUONTrackExtrap::LinearExtrapToZCov: Covariance matrix does not exist"<<endl;
130 // Extrapolate linearly track parameters to "zEnd"
131 LinearExtrapToZ(trackParam,zEnd);
135 // Compute track parameters
136 Double_t dZ = zEnd - trackParam->GetZ();
137 trackParam->SetNonBendingCoor(trackParam->GetNonBendingCoor() + trackParam->GetNonBendingSlope() * dZ);
138 trackParam->SetBendingCoor(trackParam->GetBendingCoor() + trackParam->GetBendingSlope() * dZ);
139 trackParam->SetZ(zEnd);
141 // Calculate the jacobian related to the track parameters linear extrapolation to "zEnd"
147 // Extrapolate track parameter covariances to "zEnd"
148 TMatrixD tmp(trackParam->GetCovariances(),TMatrixD::kMultTranspose,jacob);
149 TMatrixD tmp2(jacob,TMatrixD::kMult,tmp);
150 trackParam->SetCovariances(tmp2);
152 // Update the propagator if required
153 if (updatePropagator) trackParam->UpdatePropagator(jacob);
156 //__________________________________________________________________________
157 void AliMUONTrackExtrap::ExtrapToZ(AliMUONTrackParam* trackParam, Double_t zEnd)
159 /// Interface to track parameter extrapolation to the plane at "Z" using Helix or Rungekutta algorithm.
160 /// On return, the track parameters resulting from the extrapolation are updated in trackParam.
161 if (!fgFieldON) AliMUONTrackExtrap::LinearExtrapToZ(trackParam,zEnd);
162 else if (fgkUseHelix) AliMUONTrackExtrap::ExtrapToZHelix(trackParam,zEnd);
163 else AliMUONTrackExtrap::ExtrapToZRungekutta(trackParam,zEnd);
166 //__________________________________________________________________________
167 void AliMUONTrackExtrap::ExtrapToZHelix(AliMUONTrackParam* trackParam, Double_t zEnd)
169 /// Track parameter extrapolation to the plane at "Z" using Helix algorithm.
170 /// On return, the track parameters resulting from the extrapolation are updated in trackParam.
171 if (trackParam->GetZ() == zEnd) return; // nothing to be done if same Z
172 Double_t forwardBackward; // +1 if forward, -1 if backward
173 if (zEnd < trackParam->GetZ()) forwardBackward = 1.0; // spectro. z<0
174 else forwardBackward = -1.0;
175 Double_t v3[7], v3New[7]; // 7 in parameter ????
176 Int_t i3, stepNumber;
177 // For safety: return kTRUE or kFALSE ????
178 // Parameter vector for calling EXTRAP_ONESTEP
179 ConvertTrackParamForExtrap(trackParam, forwardBackward, v3);
180 // sign of charge (sign of fInverseBendingMomentum if forward motion)
181 // must be changed if backward extrapolation
182 Double_t chargeExtrap = forwardBackward * TMath::Sign(Double_t(1.0), trackParam->GetInverseBendingMomentum());
183 // Extrapolation loop
185 while (((-forwardBackward * (v3[2] - zEnd)) <= 0.0) && (stepNumber < fgkMaxStepNumber)) { // spectro. z<0
187 ExtrapOneStepHelix(chargeExtrap, fgkHelixStepLength, v3, v3New);
188 if ((-forwardBackward * (v3New[2] - zEnd)) > 0.0) break; // one is beyond Z spectro. z<0
189 // better use TArray ????
190 for (i3 = 0; i3 < 7; i3++) {v3[i3] = v3New[i3];}
192 // check fgkMaxStepNumber ????
193 // Interpolation back to exact Z (2nd order)
194 // should be in function ???? using TArray ????
195 Double_t dZ12 = v3New[2] - v3[2]; // 1->2
196 if (TMath::Abs(dZ12) > 0) {
197 Double_t dZ1i = zEnd - v3[2]; // 1-i
198 Double_t dZi2 = v3New[2] - zEnd; // i->2
199 Double_t xPrime = (v3New[0] - v3[0]) / dZ12;
200 Double_t xSecond = ((v3New[3] / v3New[5]) - (v3[3] / v3[5])) / dZ12;
201 Double_t yPrime = (v3New[1] - v3[1]) / dZ12;
202 Double_t ySecond = ((v3New[4] / v3New[5]) - (v3[4] / v3[5])) / dZ12;
203 v3[0] = v3[0] + xPrime * dZ1i - 0.5 * xSecond * dZ1i * dZi2; // X
204 v3[1] = v3[1] + yPrime * dZ1i - 0.5 * ySecond * dZ1i * dZi2; // Y
206 Double_t xPrimeI = xPrime - 0.5 * xSecond * (dZi2 - dZ1i);
207 Double_t yPrimeI = yPrime - 0.5 * ySecond * (dZi2 - dZ1i);
208 // (PX, PY, PZ)/PTOT assuming forward motion
209 v3[5] = 1.0 / TMath::Sqrt(1.0 + xPrimeI * xPrimeI + yPrimeI * yPrimeI); // PZ/PTOT
210 v3[3] = xPrimeI * v3[5]; // PX/PTOT
211 v3[4] = yPrimeI * v3[5]; // PY/PTOT
213 cout<<"W-AliMUONTrackExtrap::ExtrapToZHelix: Extrap. to Z not reached, Z = "<<zEnd<<endl;
215 // Recover track parameters (charge back for forward motion)
216 RecoverTrackParam(v3, chargeExtrap * forwardBackward, trackParam);
219 //__________________________________________________________________________
220 void AliMUONTrackExtrap::ExtrapToZRungekutta(AliMUONTrackParam* trackParam, Double_t zEnd)
222 /// Track parameter extrapolation to the plane at "Z" using Rungekutta algorithm.
223 /// On return, the track parameters resulting from the extrapolation are updated in trackParam.
224 if (trackParam->GetZ() == zEnd) return; // nothing to be done if same Z
225 Double_t forwardBackward; // +1 if forward, -1 if backward
226 if (zEnd < trackParam->GetZ()) forwardBackward = 1.0; // spectro. z<0
227 else forwardBackward = -1.0;
228 // sign of charge (sign of fInverseBendingMomentum if forward motion)
229 // must be changed if backward extrapolation
230 Double_t chargeExtrap = forwardBackward * TMath::Sign(Double_t(1.0), trackParam->GetInverseBendingMomentum());
231 Double_t v3[7], v3New[7];
233 Int_t stepNumber = 0;
235 // Extrapolation loop (until within tolerance)
236 Double_t residue = zEnd - trackParam->GetZ();
237 while (TMath::Abs(residue) > fgkRungeKuttaMaxResidue && stepNumber <= fgkMaxStepNumber) {
238 dZ = zEnd - trackParam->GetZ();
239 // step lenght assuming linear trajectory
240 step = dZ * TMath::Sqrt(1.0 + trackParam->GetBendingSlope()*trackParam->GetBendingSlope() +
241 trackParam->GetNonBendingSlope()*trackParam->GetNonBendingSlope());
242 ConvertTrackParamForExtrap(trackParam, forwardBackward, v3);
243 do { // reduce step lenght while zEnd oversteped
244 if (stepNumber > fgkMaxStepNumber) {
245 cout<<"W-AliMUONTrackExtrap::ExtrapToZRungekutta: Too many trials: "<<stepNumber<<endl;
249 step = TMath::Abs(step);
250 AliMUONTrackExtrap::ExtrapOneStepRungekutta(chargeExtrap,step,v3,v3New);
251 residue = zEnd - v3New[2];
252 step *= dZ/(v3New[2]-trackParam->GetZ());
253 } while (residue*dZ < 0 && TMath::Abs(residue) > fgkRungeKuttaMaxResidue);
254 RecoverTrackParam(v3New, chargeExtrap * forwardBackward, trackParam);
257 // terminate the extropolation with a straight line up to the exact "zEnd" value
258 trackParam->SetNonBendingCoor(trackParam->GetNonBendingCoor() + residue * trackParam->GetNonBendingSlope());
259 trackParam->SetBendingCoor(trackParam->GetBendingCoor() + residue * trackParam->GetBendingSlope());
260 trackParam->SetZ(zEnd);
263 //__________________________________________________________________________
264 void AliMUONTrackExtrap::ConvertTrackParamForExtrap(AliMUONTrackParam* trackParam, Double_t forwardBackward, Double_t *v3)
266 /// Set vector of Geant3 parameters pointed to by "v3" from track parameters in trackParam.
267 /// Since AliMUONTrackParam is only geometry, one uses "forwardBackward"
268 /// to know whether the particle is going forward (+1) or backward (-1).
269 v3[0] = trackParam->GetNonBendingCoor(); // X
270 v3[1] = trackParam->GetBendingCoor(); // Y
271 v3[2] = trackParam->GetZ(); // Z
272 Double_t pYZ = TMath::Abs(1.0 / trackParam->GetInverseBendingMomentum());
273 Double_t pZ = pYZ / TMath::Sqrt(1.0 + trackParam->GetBendingSlope() * trackParam->GetBendingSlope());
274 v3[6] = TMath::Sqrt(pYZ * pYZ + pZ * pZ * trackParam->GetNonBendingSlope() * trackParam->GetNonBendingSlope()); // PTOT
275 v3[5] = -forwardBackward * pZ / v3[6]; // PZ/PTOT spectro. z<0
276 v3[3] = trackParam->GetNonBendingSlope() * v3[5]; // PX/PTOT
277 v3[4] = trackParam->GetBendingSlope() * v3[5]; // PY/PTOT
280 //__________________________________________________________________________
281 void AliMUONTrackExtrap::RecoverTrackParam(Double_t *v3, Double_t charge, AliMUONTrackParam* trackParam)
283 /// Set track parameters in trackParam from Geant3 parameters pointed to by "v3",
284 /// assumed to be calculated for forward motion in Z.
285 /// "InverseBendingMomentum" is signed with "charge".
286 trackParam->SetNonBendingCoor(v3[0]); // X
287 trackParam->SetBendingCoor(v3[1]); // Y
288 trackParam->SetZ(v3[2]); // Z
289 Double_t pYZ = v3[6] * TMath::Sqrt((1.-v3[3])*(1.+v3[3]));
290 trackParam->SetInverseBendingMomentum(charge/pYZ);
291 trackParam->SetBendingSlope(v3[4]/v3[5]);
292 trackParam->SetNonBendingSlope(v3[3]/v3[5]);
295 //__________________________________________________________________________
296 void AliMUONTrackExtrap::ExtrapToZCov(AliMUONTrackParam* trackParam, Double_t zEnd, Bool_t updatePropagator)
298 /// Track parameters and their covariances extrapolated to the plane at "zEnd".
299 /// On return, results from the extrapolation are updated in trackParam.
301 if (trackParam->GetZ() == zEnd) return; // nothing to be done if same z
303 if (!fgFieldON) { // linear extrapolation if no magnetic field
304 AliMUONTrackExtrap::LinearExtrapToZCov(trackParam,zEnd,updatePropagator);
308 // No need to propagate the covariance matrix if it does not exist
309 if (!trackParam->CovariancesExist()) {
310 cout<<"W-AliMUONTrackExtrap::ExtrapToZCov: Covariance matrix does not exist"<<endl;
311 // Extrapolate track parameters to "zEnd"
312 ExtrapToZ(trackParam,zEnd);
316 // Save the actual track parameters
317 AliMUONTrackParam trackParamSave(*trackParam);
318 TMatrixD paramSave(trackParamSave.GetParameters());
319 Double_t zBegin = trackParamSave.GetZ();
321 // Get reference to the parameter covariance matrix
322 const TMatrixD& kParamCov = trackParam->GetCovariances();
324 // Extrapolate track parameters to "zEnd"
325 ExtrapToZ(trackParam,zEnd);
327 // Get reference to the extrapolated parameters
328 const TMatrixD& extrapParam = trackParam->GetParameters();
330 // Calculate the jacobian related to the track parameters extrapolation to "zEnd"
333 TMatrixD dParam(5,1);
334 Double_t direction[5] = {-1.,-1.,1.,1.,-1.};
335 for (Int_t i=0; i<5; i++) {
336 // Skip jacobian calculation for parameters with no associated error
337 if (kParamCov(i,i) <= 0.) continue;
339 // Small variation of parameter i only
340 for (Int_t j=0; j<5; j++) {
342 dParam(j,0) = TMath::Sqrt(kParamCov(i,i));
343 dParam(j,0) *= TMath::Sign(1.,direction[j]*paramSave(j,0)); // variation always in the same direction
344 } else dParam(j,0) = 0.;
347 // Set new parameters
348 trackParamSave.SetParameters(paramSave);
349 trackParamSave.AddParameters(dParam);
350 trackParamSave.SetZ(zBegin);
352 // Extrapolate new track parameters to "zEnd"
353 ExtrapToZ(&trackParamSave,zEnd);
355 // Calculate the jacobian
356 TMatrixD jacobji(trackParamSave.GetParameters(),TMatrixD::kMinus,extrapParam);
357 jacobji *= 1. / dParam(i,0);
358 jacob.SetSub(0,i,jacobji);
361 // Extrapolate track parameter covariances to "zEnd"
362 TMatrixD tmp(kParamCov,TMatrixD::kMultTranspose,jacob);
363 TMatrixD tmp2(jacob,TMatrixD::kMult,tmp);
364 trackParam->SetCovariances(tmp2);
366 // Update the propagator if required
367 if (updatePropagator) trackParam->UpdatePropagator(jacob);
370 //__________________________________________________________________________
371 void AliMUONTrackExtrap::AddMCSEffectInAbsorber(AliMUONTrackParam* param, Double_t pathLength, Double_t f0, Double_t f1, Double_t f2)
373 /// Add to the track parameter covariances the effects of multiple Coulomb scattering
374 /// The absorber correction parameters are supposed to be calculated at the current track z-position
376 // absorber related covariance parameters
377 Double_t bendingSlope = param->GetBendingSlope();
378 Double_t nonBendingSlope = param->GetNonBendingSlope();
379 Double_t inverseBendingMomentum = param->GetInverseBendingMomentum();
380 Double_t alpha2 = 0.0136 * 0.0136 * inverseBendingMomentum * inverseBendingMomentum * (1.0 + bendingSlope * bendingSlope) /
381 (1.0 + bendingSlope *bendingSlope + nonBendingSlope * nonBendingSlope); // velocity = 1
382 Double_t varCoor = alpha2 * (pathLength * pathLength * f0 - 2. * pathLength * f1 + f2);
383 Double_t covCorrSlope = alpha2 * (pathLength * f0 - f1);
384 Double_t varSlop = alpha2 * f0;
386 // Set MCS covariance matrix
387 TMatrixD newParamCov(param->GetCovariances());
389 newParamCov(0,0) += varCoor; newParamCov(0,1) += covCorrSlope;
390 newParamCov(1,0) += covCorrSlope; newParamCov(1,1) += varSlop;
392 newParamCov(2,2) += varCoor; newParamCov(2,3) += covCorrSlope;
393 newParamCov(3,2) += covCorrSlope; newParamCov(3,3) += varSlop;
395 // Set momentum related covariances if B!=0
397 // compute derivative d(q/Pxy) / dSlopeX and d(q/Pxy) / dSlopeY
398 Double_t dqPxydSlopeX = inverseBendingMomentum * nonBendingSlope / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
399 Double_t dqPxydSlopeY = - inverseBendingMomentum * nonBendingSlope*nonBendingSlope * bendingSlope /
400 (1. + bendingSlope*bendingSlope) / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
401 // Inverse bending momentum (due to dependences with bending and non bending slopes)
402 newParamCov(4,0) += dqPxydSlopeX * covCorrSlope; newParamCov(0,4) += dqPxydSlopeX * covCorrSlope;
403 newParamCov(4,1) += dqPxydSlopeX * varSlop; newParamCov(1,4) += dqPxydSlopeX * varSlop;
404 newParamCov(4,2) += dqPxydSlopeY * covCorrSlope; newParamCov(2,4) += dqPxydSlopeY * covCorrSlope;
405 newParamCov(4,3) += dqPxydSlopeY * varSlop; newParamCov(3,4) += dqPxydSlopeY * varSlop;
406 newParamCov(4,4) += (dqPxydSlopeX*dqPxydSlopeX + dqPxydSlopeY*dqPxydSlopeY) * varSlop;
409 // Set new covariances
410 param->SetCovariances(newParamCov);
413 //__________________________________________________________________________
414 void AliMUONTrackExtrap::CorrectMCSEffectInAbsorber(AliMUONTrackParam* param,
415 Double_t xVtx, Double_t yVtx, Double_t zVtx,
416 Double_t errXVtx, Double_t errYVtx,
417 Double_t absZBeg, Double_t pathLength, Double_t f0, Double_t f1, Double_t f2)
419 /// Correct parameters and corresponding covariances using Branson correction
420 /// - input param are parameters and covariances at the end of absorber
421 /// - output param are parameters and covariances at vertex
422 /// Absorber correction parameters are supposed to be calculated at the current track z-position
424 // Position of the Branson plane (spectro. (z<0))
425 Double_t zB = (f1>0.) ? absZBeg - f2/f1 : 0.;
427 // Add MCS effects to current parameter covariances
428 AddMCSEffectInAbsorber(param, pathLength, f0, f1, f2);
430 // Get track parameters and covariances in the Branson plane corrected for magnetic field effect
431 ExtrapToZCov(param,zVtx);
432 LinearExtrapToZCov(param,zB);
434 // compute track parameters at vertex
435 TMatrixD newParam(5,1);
436 newParam(0,0) = xVtx;
437 newParam(1,0) = (param->GetNonBendingCoor() - xVtx) / (zB - zVtx);
438 newParam(2,0) = yVtx;
439 newParam(3,0) = (param->GetBendingCoor() - yVtx) / (zB - zVtx);
440 newParam(4,0) = param->GetCharge() / param->P() *
441 TMath::Sqrt(1.0 + newParam(1,0)*newParam(1,0) + newParam(3,0)*newParam(3,0)) /
442 TMath::Sqrt(1.0 + newParam(3,0)*newParam(3,0));
444 // Get covariances in (X, SlopeX, Y, SlopeY, q*PTot) coordinate system
445 TMatrixD paramCovP(param->GetCovariances());
446 Cov2CovP(param->GetParameters(),paramCovP);
448 // Get the covariance matrix in the (XVtx, X, YVtx, Y, q*PTot) coordinate system
449 TMatrixD paramCovVtx(5,5);
451 paramCovVtx(0,0) = errXVtx * errXVtx;
452 paramCovVtx(1,1) = paramCovP(0,0);
453 paramCovVtx(2,2) = errYVtx * errYVtx;
454 paramCovVtx(3,3) = paramCovP(2,2);
455 paramCovVtx(4,4) = paramCovP(4,4);
456 paramCovVtx(1,3) = paramCovP(0,2);
457 paramCovVtx(3,1) = paramCovP(2,0);
458 paramCovVtx(1,4) = paramCovP(0,4);
459 paramCovVtx(4,1) = paramCovP(4,0);
460 paramCovVtx(3,4) = paramCovP(2,4);
461 paramCovVtx(4,3) = paramCovP(4,2);
463 // Jacobian of the transformation (XVtx, X, YVtx, Y, q*PTot) -> (XVtx, SlopeXVtx, YVtx, SlopeYVtx, q*PTotVtx)
466 jacob(1,0) = - 1. / (zB - zVtx);
467 jacob(1,1) = 1. / (zB - zVtx);
468 jacob(3,2) = - 1. / (zB - zVtx);
469 jacob(3,3) = 1. / (zB - zVtx);
471 // Compute covariances at vertex in the (XVtx, SlopeXVtx, YVtx, SlopeYVtx, q*PTotVtx) coordinate system
472 TMatrixD tmp(paramCovVtx,TMatrixD::kMultTranspose,jacob);
473 TMatrixD newParamCov(jacob,TMatrixD::kMult,tmp);
475 // Compute covariances at vertex in the (XVtx, SlopeXVtx, YVtx, SlopeYVtx, q/PyzVtx) coordinate system
476 CovP2Cov(newParam,newParamCov);
478 // Set parameters and covariances at vertex
479 param->SetParameters(newParam);
481 param->SetCovariances(newParamCov);
484 //__________________________________________________________________________
485 void AliMUONTrackExtrap::CorrectELossEffectInAbsorber(AliMUONTrackParam* param, Double_t eLoss, Double_t sigmaELoss2)
487 /// Correct parameters for energy loss and add energy loss fluctuation effect to covariances
489 // Get parameter covariances in (X, SlopeX, Y, SlopeY, q*PTot) coordinate system
490 TMatrixD newParamCov(param->GetCovariances());
491 Cov2CovP(param->GetParameters(),newParamCov);
493 // Compute new parameters corrected for energy loss
494 Double_t muMass = TDatabasePDG::Instance()->GetParticle("mu-")->Mass(); // GeV
495 Double_t p = param->P();
496 Double_t e = TMath::Sqrt(p*p + muMass*muMass);
497 Double_t eCorr = e + eLoss;
498 Double_t pCorr = TMath::Sqrt(eCorr*eCorr - muMass*muMass);
499 Double_t nonBendingSlope = param->GetNonBendingSlope();
500 Double_t bendingSlope = param->GetBendingSlope();
501 param->SetInverseBendingMomentum(param->GetCharge() / pCorr *
502 TMath::Sqrt(1.0 + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope) /
503 TMath::Sqrt(1.0 + bendingSlope*bendingSlope));
505 // Add effects of energy loss fluctuation to covariances
506 newParamCov(4,4) += eCorr * eCorr / pCorr / pCorr * sigmaELoss2;
508 // Get new parameter covariances in (X, SlopeX, Y, SlopeY, q/Pyz) coordinate system
509 CovP2Cov(param->GetParameters(),newParamCov);
511 // Set new parameter covariances
512 param->SetCovariances(newParamCov);
515 //__________________________________________________________________________
516 Bool_t AliMUONTrackExtrap::GetAbsorberCorrectionParam(Double_t trackXYZIn[3], Double_t trackXYZOut[3], Double_t pTotal,
517 Double_t &pathLength, Double_t &f0, Double_t &f1, Double_t &f2,
518 Double_t &meanRho, Double_t &totalELoss, Double_t &sigmaELoss2)
520 /// Parameters used to correct for Multiple Coulomb Scattering and energy loss in absorber
521 /// Calculated assuming a linear propagation from trackXYZIn to trackXYZOut (order is important)
522 // pathLength: path length between trackXYZIn and trackXYZOut (cm)
523 // f0: 0th moment of z calculated with the inverse radiation-length distribution
524 // f1: 1st moment of z calculated with the inverse radiation-length distribution
525 // f2: 2nd moment of z calculated with the inverse radiation-length distribution
526 // meanRho: average density of crossed material (g/cm3)
527 // totalELoss: total energy loss in absorber
529 // Reset absorber's parameters
538 // Check whether the geometry is available
540 cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: no TGeo"<<endl;
544 // Initialize starting point and direction
545 pathLength = TMath::Sqrt((trackXYZOut[0] - trackXYZIn[0])*(trackXYZOut[0] - trackXYZIn[0])+
546 (trackXYZOut[1] - trackXYZIn[1])*(trackXYZOut[1] - trackXYZIn[1])+
547 (trackXYZOut[2] - trackXYZIn[2])*(trackXYZOut[2] - trackXYZIn[2]));
548 if (pathLength < TGeoShape::Tolerance()) return kFALSE;
550 b[0] = (trackXYZOut[0] - trackXYZIn[0]) / pathLength;
551 b[1] = (trackXYZOut[1] - trackXYZIn[1]) / pathLength;
552 b[2] = (trackXYZOut[2] - trackXYZIn[2]) / pathLength;
553 TGeoNode *currentnode = gGeoManager->InitTrack(trackXYZIn, b);
555 cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: start point out of geometry"<<endl;
559 // loop over absorber slices and calculate absorber's parameters
560 Double_t rho = 0.; // material density (g/cm3)
561 Double_t x0 = 0.; // radiation-length (cm-1)
562 Double_t atomicA = 0.; // A of material
563 Double_t atomicZ = 0.; // Z of material
564 Double_t localPathLength = 0;
565 Double_t remainingPathLength = pathLength;
566 Double_t zB = trackXYZIn[2];
567 Double_t zE, dzB, dzE;
569 // Get material properties
570 TGeoMaterial *material = currentnode->GetVolume()->GetMedium()->GetMaterial();
571 rho = material->GetDensity();
572 x0 = material->GetRadLen();
573 if (!material->IsMixture()) x0 /= rho; // different normalization in the modeler for mixture
574 atomicA = material->GetA();
575 atomicZ = material->GetZ();
577 // Get path length within this material
578 gGeoManager->FindNextBoundary(remainingPathLength);
579 localPathLength = gGeoManager->GetStep() + 1.e-6;
580 // Check if boundary within remaining path length. If so, make sure to cross the boundary to prepare the next step
581 if (localPathLength >= remainingPathLength) localPathLength = remainingPathLength;
583 currentnode = gGeoManager->Step();
585 cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: navigation failed"<<endl;
586 f0 = f1 = f2 = meanRho = totalELoss = sigmaELoss2 = 0.;
589 if (!gGeoManager->IsEntering()) {
590 // make another small step to try to enter in new absorber slice
591 gGeoManager->SetStep(0.001);
592 currentnode = gGeoManager->Step();
593 if (!gGeoManager->IsEntering() || !currentnode) {
594 cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: navigation failed"<<endl;
595 f0 = f1 = f2 = meanRho = totalELoss = sigmaELoss2 = 0.;
598 localPathLength += 0.001;
602 // calculate absorber's parameters
603 zE = b[2] * localPathLength + zB;
604 dzB = zB - trackXYZIn[2];
605 dzE = zE - trackXYZIn[2];
606 f0 += localPathLength / x0;
607 f1 += (dzE*dzE - dzB*dzB) / b[2] / b[2] / x0 / 2.;
608 f2 += (dzE*dzE*dzE - dzB*dzB*dzB) / b[2] / b[2] / b[2] / x0 / 3.;
609 meanRho += localPathLength * rho;
610 totalELoss += BetheBloch(pTotal, localPathLength, rho, atomicA, atomicZ);
611 sigmaELoss2 += EnergyLossFluctuation2(pTotal, localPathLength, rho, atomicA, atomicZ);
615 remainingPathLength -= localPathLength;
616 } while (remainingPathLength > TGeoShape::Tolerance());
618 meanRho /= pathLength;
623 //__________________________________________________________________________
624 Double_t AliMUONTrackExtrap::GetMCSAngle2(const AliMUONTrackParam& param, Double_t dZ, Double_t x0)
626 /// Return the angular dispersion square due to multiple Coulomb scattering
627 /// through a material of thickness "dZ" and of radiation length "x0"
628 /// assuming linear propagation and using the small angle approximation.
630 Double_t bendingSlope = param.GetBendingSlope();
631 Double_t nonBendingSlope = param.GetNonBendingSlope();
632 Double_t inverseTotalMomentum2 = param.GetInverseBendingMomentum() * param.GetInverseBendingMomentum() *
633 (1.0 + bendingSlope * bendingSlope) /
634 (1.0 + bendingSlope *bendingSlope + nonBendingSlope * nonBendingSlope);
635 // Path length in the material
636 Double_t pathLength = TMath::Abs(dZ) * TMath::Sqrt(1.0 + bendingSlope*bendingSlope + nonBendingSlope*nonBendingSlope);
637 // relativistic velocity
639 // Angular dispersion square of the track (variance) in a plane perpendicular to the trajectory
640 Double_t theta02 = 0.0136 / velo * (1 + 0.038 * TMath::Log(pathLength/x0));
642 return theta02 * theta02 * inverseTotalMomentum2 * pathLength / x0;
645 //__________________________________________________________________________
646 void AliMUONTrackExtrap::AddMCSEffect(AliMUONTrackParam *param, Double_t dZ, Double_t x0)
648 /// Add to the track parameter covariances the effects of multiple Coulomb scattering
649 /// through a material of thickness "dZ" and of radiation length "x0"
650 /// assuming linear propagation and using the small angle approximation.
652 Double_t bendingSlope = param->GetBendingSlope();
653 Double_t nonBendingSlope = param->GetNonBendingSlope();
654 Double_t inverseBendingMomentum = param->GetInverseBendingMomentum();
655 Double_t inverseTotalMomentum2 = inverseBendingMomentum * inverseBendingMomentum *
656 (1.0 + bendingSlope * bendingSlope) /
657 (1.0 + bendingSlope *bendingSlope + nonBendingSlope * nonBendingSlope);
658 // Path length in the material
659 Double_t pathLength = TMath::Abs(dZ) * TMath::Sqrt(1.0 + bendingSlope*bendingSlope + nonBendingSlope*nonBendingSlope);
660 Double_t pathLength2 = pathLength * pathLength;
661 // relativistic velocity
663 // Angular dispersion square of the track (variance) in a plane perpendicular to the trajectory
664 Double_t theta02 = 0.0136 / velo * (1 + 0.038 * TMath::Log(pathLength/x0));
665 theta02 *= theta02 * inverseTotalMomentum2 * pathLength / x0;
667 Double_t varCoor = pathLength2 * theta02 / 3.;
668 Double_t varSlop = theta02;
669 Double_t covCorrSlope = pathLength * theta02 / 2.;
671 // Set MCS covariance matrix
672 TMatrixD newParamCov(param->GetCovariances());
674 newParamCov(0,0) += varCoor; newParamCov(0,1) += covCorrSlope;
675 newParamCov(1,0) += covCorrSlope; newParamCov(1,1) += varSlop;
677 newParamCov(2,2) += varCoor; newParamCov(2,3) += covCorrSlope;
678 newParamCov(3,2) += covCorrSlope; newParamCov(3,3) += varSlop;
680 // Set momentum related covariances if B!=0
682 // compute derivative d(q/Pxy) / dSlopeX and d(q/Pxy) / dSlopeY
683 Double_t dqPxydSlopeX = inverseBendingMomentum * nonBendingSlope / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
684 Double_t dqPxydSlopeY = - inverseBendingMomentum * nonBendingSlope*nonBendingSlope * bendingSlope /
685 (1. + bendingSlope*bendingSlope) / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
686 // Inverse bending momentum (due to dependences with bending and non bending slopes)
687 newParamCov(4,0) += dqPxydSlopeX * covCorrSlope; newParamCov(0,4) += dqPxydSlopeX * covCorrSlope;
688 newParamCov(4,1) += dqPxydSlopeX * varSlop; newParamCov(1,4) += dqPxydSlopeX * varSlop;
689 newParamCov(4,2) += dqPxydSlopeY * covCorrSlope; newParamCov(2,4) += dqPxydSlopeY * covCorrSlope;
690 newParamCov(4,3) += dqPxydSlopeY * varSlop; newParamCov(3,4) += dqPxydSlopeY * varSlop;
691 newParamCov(4,4) += (dqPxydSlopeX*dqPxydSlopeX + dqPxydSlopeY*dqPxydSlopeY) * varSlop;
694 // Set new covariances
695 param->SetCovariances(newParamCov);
698 //__________________________________________________________________________
699 void AliMUONTrackExtrap::ExtrapToVertex(AliMUONTrackParam* trackParam,
700 Double_t xVtx, Double_t yVtx, Double_t zVtx,
701 Double_t errXVtx, Double_t errYVtx,
702 Bool_t correctForMCS, Bool_t correctForEnergyLoss)
704 /// Main method for extrapolation to the vertex:
705 /// Returns the track parameters and covariances resulting from the extrapolation of the current trackParam
706 /// Changes parameters and covariances according to multiple scattering and energy loss corrections:
707 /// if correctForMCS=kTRUE: compute parameters using Branson correction and add correction resolution to covariances
708 /// if correctForMCS=kFALSE: add parameter dispersion due to MCS in parameter covariances
709 /// if correctForEnergyLoss=kTRUE: correct parameters for energy loss and add energy loss fluctuation to covariances
710 /// if correctForEnergyLoss=kFALSE: do nothing about energy loss
712 if (trackParam->GetZ() == zVtx) return; // nothing to be done if already at vertex
714 if (trackParam->GetZ() > zVtx) { // spectro. (z<0)
715 cout<<"E-AliMUONTrackExtrap::ExtrapToVertex: Starting Z ("<<trackParam->GetZ()
716 <<") upstream the vertex (zVtx = "<<zVtx<<")"<<endl;
720 // Check the vertex position relatively to the absorber
721 if (zVtx < AliMUONConstants::AbsZBeg() && zVtx > AliMUONConstants::AbsZEnd()) { // spectro. (z<0)
722 cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Ending Z ("<<zVtx
723 <<") inside the front absorber ("<<AliMUONConstants::AbsZBeg()<<","<<AliMUONConstants::AbsZEnd()<<")"<<endl;
724 } else if (zVtx < AliMUONConstants::AbsZEnd() ) { // spectro. (z<0)
725 cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Ending Z ("<<zVtx
726 <<") downstream the front absorber (zAbsorberEnd = "<<AliMUONConstants::AbsZEnd()<<")"<<endl;
727 if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,zVtx);
728 else ExtrapToZ(trackParam,zVtx);
732 // Check the track position relatively to the absorber and extrapolate track parameters to the end of the absorber if needed
733 if (trackParam->GetZ() > AliMUONConstants::AbsZBeg()) { // spectro. (z<0)
734 cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Starting Z ("<<trackParam->GetZ()
735 <<") upstream the front absorber (zAbsorberBegin = "<<AliMUONConstants::AbsZBeg()<<")"<<endl;
736 if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,zVtx);
737 else ExtrapToZ(trackParam,zVtx);
739 } else if (trackParam->GetZ() > AliMUONConstants::AbsZEnd()) { // spectro. (z<0)
740 cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Starting Z ("<<trackParam->GetZ()
741 <<") inside the front absorber ("<<AliMUONConstants::AbsZBeg()<<","<<AliMUONConstants::AbsZEnd()<<")"<<endl;
743 if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,AliMUONConstants::AbsZEnd());
744 else ExtrapToZ(trackParam,AliMUONConstants::AbsZEnd());
747 // Get absorber correction parameters assuming linear propagation in absorber
748 Double_t trackXYZOut[3];
749 trackXYZOut[0] = trackParam->GetNonBendingCoor();
750 trackXYZOut[1] = trackParam->GetBendingCoor();
751 trackXYZOut[2] = trackParam->GetZ();
752 Double_t trackXYZIn[3];
753 if (correctForMCS) { // assume linear propagation until the vertex
754 trackXYZIn[2] = TMath::Min(zVtx, AliMUONConstants::AbsZBeg()); // spectro. (z<0)
755 trackXYZIn[0] = trackXYZOut[0] + (xVtx - trackXYZOut[0]) / (zVtx - trackXYZOut[2]) * (trackXYZIn[2] - trackXYZOut[2]);
756 trackXYZIn[1] = trackXYZOut[1] + (yVtx - trackXYZOut[1]) / (zVtx - trackXYZOut[2]) * (trackXYZIn[2] - trackXYZOut[2]);
758 AliMUONTrackParam trackParamIn(*trackParam);
759 ExtrapToZ(&trackParamIn, TMath::Min(zVtx, AliMUONConstants::AbsZBeg()));
760 trackXYZIn[0] = trackParamIn.GetNonBendingCoor();
761 trackXYZIn[1] = trackParamIn.GetBendingCoor();
762 trackXYZIn[2] = trackParamIn.GetZ();
764 Double_t pTot = trackParam->P();
765 Double_t pathLength, f0, f1, f2, meanRho, totalELoss, sigmaELoss2;
766 if (!GetAbsorberCorrectionParam(trackXYZIn,trackXYZOut,pTot,pathLength,f0,f1,f2,meanRho,totalELoss,sigmaELoss2)) {
767 cout<<"E-AliMUONTrackExtrap::ExtrapToVertex: Unable to take into account the absorber effects"<<endl;
768 if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,zVtx);
769 else ExtrapToZ(trackParam,zVtx);
773 // Compute track parameters and covariances at vertex according to correctForMCS and correctForEnergyLoss flags
776 if (correctForEnergyLoss) {
778 // Correct for multiple scattering and energy loss
779 CorrectELossEffectInAbsorber(trackParam, 0.5*totalELoss, 0.5*sigmaELoss2);
780 CorrectMCSEffectInAbsorber(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx,
781 trackXYZIn[2], pathLength, f0, f1, f2);
782 CorrectELossEffectInAbsorber(trackParam, 0.5*totalELoss, 0.5*sigmaELoss2);
786 // Correct for multiple scattering
787 CorrectMCSEffectInAbsorber(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx,
788 trackXYZIn[2], pathLength, f0, f1, f2);
793 if (correctForEnergyLoss) {
795 // Correct for energy loss add multiple scattering dispersion in covariance matrix
796 CorrectELossEffectInAbsorber(trackParam, 0.5*totalELoss, 0.5*sigmaELoss2);
797 AddMCSEffectInAbsorber(trackParam, pathLength, f0, f1, f2);
798 ExtrapToZCov(trackParam, trackXYZIn[2]);
799 CorrectELossEffectInAbsorber(trackParam, 0.5*totalELoss, 0.5*sigmaELoss2);
800 ExtrapToZCov(trackParam, zVtx);
804 // add multiple scattering dispersion in covariance matrix
805 AddMCSEffectInAbsorber(trackParam, pathLength, f0, f1, f2);
806 ExtrapToZCov(trackParam, zVtx);
814 //__________________________________________________________________________
815 void AliMUONTrackExtrap::ExtrapToVertex(AliMUONTrackParam* trackParam,
816 Double_t xVtx, Double_t yVtx, Double_t zVtx,
817 Double_t errXVtx, Double_t errYVtx)
819 /// Extrapolate track parameters to vertex, corrected for multiple scattering and energy loss effects
820 /// Add branson correction resolution and energy loss fluctuation to parameter covariances
821 ExtrapToVertex(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx, kTRUE, kTRUE);
824 //__________________________________________________________________________
825 void AliMUONTrackExtrap::ExtrapToVertexWithoutELoss(AliMUONTrackParam* trackParam,
826 Double_t xVtx, Double_t yVtx, Double_t zVtx,
827 Double_t errXVtx, Double_t errYVtx)
829 /// Extrapolate track parameters to vertex, corrected for multiple scattering effects only
830 /// Add branson correction resolution to parameter covariances
831 ExtrapToVertex(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx, kTRUE, kFALSE);
834 //__________________________________________________________________________
835 void AliMUONTrackExtrap::ExtrapToVertexWithoutBranson(AliMUONTrackParam* trackParam, Double_t zVtx)
837 /// Extrapolate track parameters to vertex, corrected for energy loss effects only
838 /// Add dispersion due to multiple scattering and energy loss fluctuation to parameter covariances
839 ExtrapToVertex(trackParam, 0., 0., zVtx, 0., 0., kFALSE, kTRUE);
842 //__________________________________________________________________________
843 void AliMUONTrackExtrap::ExtrapToVertexUncorrected(AliMUONTrackParam* trackParam, Double_t zVtx)
845 /// Extrapolate track parameters to vertex without multiple scattering and energy loss corrections
846 /// Add dispersion due to multiple scattering to parameter covariances
847 ExtrapToVertex(trackParam, 0., 0., zVtx, 0., 0., kFALSE, kFALSE);
850 //__________________________________________________________________________
851 Double_t AliMUONTrackExtrap::TotalMomentumEnergyLoss(AliMUONTrackParam* trackParam, Double_t xVtx, Double_t yVtx, Double_t zVtx)
853 /// Calculate the total momentum energy loss in-between the track position and the vertex assuming a linear propagation
855 if (trackParam->GetZ() == zVtx) return 0.; // nothing to be done if already at vertex
857 // Check whether the geometry is available
859 cout<<"E-AliMUONTrackExtrap::TotalMomentumEnergyLoss: no TGeo"<<endl;
863 // Get encountered material correction parameters assuming linear propagation from vertex to the track position
864 Double_t trackXYZOut[3];
865 trackXYZOut[0] = trackParam->GetNonBendingCoor();
866 trackXYZOut[1] = trackParam->GetBendingCoor();
867 trackXYZOut[2] = trackParam->GetZ();
868 Double_t trackXYZIn[3];
869 trackXYZIn[0] = xVtx;
870 trackXYZIn[1] = yVtx;
871 trackXYZIn[2] = zVtx;
872 Double_t pTot = trackParam->P();
873 Double_t pathLength, f0, f1, f2, meanRho, totalELoss, sigmaELoss2;
874 GetAbsorberCorrectionParam(trackXYZIn,trackXYZOut,pTot,pathLength,f0,f1,f2,meanRho,totalELoss,sigmaELoss2);
876 // total momentum corrected for energy loss
877 Double_t muMass = TDatabasePDG::Instance()->GetParticle("mu-")->Mass(); // GeV
878 Double_t e = TMath::Sqrt(pTot*pTot + muMass*muMass);
879 Double_t eCorr = e + totalELoss;
880 Double_t pTotCorr = TMath::Sqrt(eCorr*eCorr - muMass*muMass);
882 return pTotCorr - pTot;
885 //__________________________________________________________________________
886 Double_t AliMUONTrackExtrap::BetheBloch(Double_t pTotal, Double_t pathLength, Double_t rho, Double_t atomicA, Double_t atomicZ)
888 /// Returns the mean total momentum energy loss of muon with total momentum='pTotal'
889 /// in the absorber layer of lenght='pathLength', density='rho', A='atomicA' and Z='atomicZ'
890 Double_t muMass = TDatabasePDG::Instance()->GetParticle("mu-")->Mass(); // GeV
892 // mean exitation energy (GeV)
894 if (atomicZ < 13) i = (12. * atomicZ + 7.) * 1.e-9;
895 else i = (9.76 * atomicZ + 58.8 * TMath::Power(atomicZ,-0.19)) * 1.e-9;
897 return pathLength * rho * AliExternalTrackParam::BetheBlochGeant(pTotal/muMass, rho, 0.20, 3.00, i, atomicZ/atomicA);
900 //__________________________________________________________________________
901 Double_t AliMUONTrackExtrap::EnergyLossFluctuation2(Double_t pTotal, Double_t pathLength, Double_t rho, Double_t atomicA, Double_t atomicZ)
903 /// Returns the total momentum energy loss fluctuation of muon with total momentum='pTotal'
904 /// in the absorber layer of lenght='pathLength', density='rho', A='atomicA' and Z='atomicZ'
905 Double_t muMass = TDatabasePDG::Instance()->GetParticle("mu-")->Mass(); // GeV
906 //Double_t eMass = 0.510998918e-3; // GeV
907 Double_t k = 0.307075e-3; // GeV.g^-1.cm^2
908 Double_t p2=pTotal*pTotal;
909 Double_t beta2=p2/(p2 + muMass*muMass);
911 Double_t fwhm = 2. * k * rho * pathLength * atomicZ / atomicA / beta2; // FWHM of the energy loss Landau distribution
912 Double_t sigma2 = fwhm * fwhm / (8.*log(2.)); // gaussian: fwmh = 2 * srqt(2*ln(2)) * sigma (i.e. fwmh = 2.35 * sigma)
914 //sigma2 = k * rho * pathLength * atomicZ / atomicA * eMass; // sigma2 of the energy loss gaussian distribution
919 //__________________________________________________________________________
920 void AliMUONTrackExtrap::Cov2CovP(const TMatrixD ¶m, TMatrixD &cov)
922 /// change coordinate system: (X, SlopeX, Y, SlopeY, q/Pyz) -> (X, SlopeX, Y, SlopeY, q*PTot)
923 /// parameters (param) are given in the (X, SlopeX, Y, SlopeY, q/Pyz) coordinate system
925 // charge * total momentum
926 Double_t qPTot = TMath::Sqrt(1. + param(1,0)*param(1,0) + param(3,0)*param(3,0)) /
927 TMath::Sqrt(1. + param(3,0)*param(3,0)) / param(4,0);
929 // Jacobian of the opposite transformation
932 jacob(4,1) = qPTot * param(1,0) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
933 jacob(4,3) = - qPTot * param(1,0) * param(1,0) * param(3,0) /
934 (1. + param(3,0)*param(3,0)) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
935 jacob(4,4) = - qPTot / param(4,0);
937 // compute covariances in new coordinate system
938 TMatrixD tmp(cov,TMatrixD::kMultTranspose,jacob);
942 //__________________________________________________________________________
943 void AliMUONTrackExtrap::CovP2Cov(const TMatrixD ¶m, TMatrixD &covP)
945 /// change coordinate system: (X, SlopeX, Y, SlopeY, q*PTot) -> (X, SlopeX, Y, SlopeY, q/Pyz)
946 /// parameters (param) are given in the (X, SlopeX, Y, SlopeY, q/Pyz) coordinate system
948 // charge * total momentum
949 Double_t qPTot = TMath::Sqrt(1. + param(1,0)*param(1,0) + param(3,0)*param(3,0)) /
950 TMath::Sqrt(1. + param(3,0)*param(3,0)) / param(4,0);
952 // Jacobian of the transformation
955 jacob(4,1) = param(4,0) * param(1,0) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
956 jacob(4,3) = - param(4,0) * param(1,0) * param(1,0) * param(3,0) /
957 (1. + param(3,0)*param(3,0)) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
958 jacob(4,4) = - param(4,0) / qPTot;
960 // compute covariances in new coordinate system
961 TMatrixD tmp(covP,TMatrixD::kMultTranspose,jacob);
962 covP.Mult(jacob,tmp);
965 //__________________________________________________________________________
966 void AliMUONTrackExtrap::ExtrapOneStepHelix(Double_t charge, Double_t step, Double_t *vect, Double_t *vout)
969 /// ******************************************************************
971 /// * Performs the tracking of one step in a magnetic field *
972 /// * The trajectory is assumed to be a helix in a constant field *
973 /// * taken at the mid point of the step. *
976 /// * STEP =arc length of the step asked *
977 /// * VECT =input vector (position,direction cos and momentum) *
978 /// * CHARGE= electric charge of the particle *
980 /// * VOUT = same as VECT after completion of the step *
982 /// * ==>Called by : USER, GUSWIM *
983 /// * Author m.hansroul ********* *
984 /// * modified s.egli, s.v.levonian *
985 /// * modified v.perevoztchikov
987 /// ******************************************************************
990 // modif: everything in double precision
992 Double_t xyz[3], h[4], hxp[3];
993 Double_t h2xy, hp, rho, tet;
994 Double_t sint, sintt, tsint, cos1t;
995 Double_t f1, f2, f3, f4, f5, f6;
1000 const Int_t kipx = 3;
1001 const Int_t kipy = 4;
1002 const Int_t kipz = 5;
1003 const Int_t kipp = 6;
1005 const Double_t kec = 2.9979251e-4;
1007 // ------------------------------------------------------------------
1009 // units are kgauss,centimeters,gev/c
1011 vout[kipp] = vect[kipp];
1012 if (TMath::Abs(charge) < 0.00001) {
1013 for (Int_t i = 0; i < 3; i++) {
1014 vout[i] = vect[i] + step * vect[i+3];
1015 vout[i+3] = vect[i+3];
1019 xyz[0] = vect[kix] + 0.5 * step * vect[kipx];
1020 xyz[1] = vect[kiy] + 0.5 * step * vect[kipy];
1021 xyz[2] = vect[kiz] + 0.5 * step * vect[kipz];
1023 //cmodif: call gufld (xyz, h) changed into:
1024 TGeoGlobalMagField::Instance()->Field(xyz,h);
1026 h2xy = h[0]*h[0] + h[1]*h[1];
1027 h[3] = h[2]*h[2]+ h2xy;
1028 if (h[3] < 1.e-12) {
1029 for (Int_t i = 0; i < 3; i++) {
1030 vout[i] = vect[i] + step * vect[i+3];
1031 vout[i+3] = vect[i+3];
1035 if (h2xy < 1.e-12*h[3]) {
1036 ExtrapOneStepHelix3(charge*h[2], step, vect, vout);
1039 h[3] = TMath::Sqrt(h[3]);
1045 hxp[0] = h[1]*vect[kipz] - h[2]*vect[kipy];
1046 hxp[1] = h[2]*vect[kipx] - h[0]*vect[kipz];
1047 hxp[2] = h[0]*vect[kipy] - h[1]*vect[kipx];
1049 hp = h[0]*vect[kipx] + h[1]*vect[kipy] + h[2]*vect[kipz];
1051 rho = -charge*h[3]/vect[kipp];
1054 if (TMath::Abs(tet) > 0.15) {
1055 sint = TMath::Sin(tet);
1057 tsint = (tet-sint)/tet;
1058 cos1t = 2.*(TMath::Sin(0.5*tet))*(TMath::Sin(0.5*tet))/tet;
1060 tsint = tet*tet/36.;
1061 sintt = (1. - tsint);
1068 f3 = step * tsint * hp;
1071 f6 = tet * cos1t * hp;
1073 vout[kix] = vect[kix] + f1*vect[kipx] + f2*hxp[0] + f3*h[0];
1074 vout[kiy] = vect[kiy] + f1*vect[kipy] + f2*hxp[1] + f3*h[1];
1075 vout[kiz] = vect[kiz] + f1*vect[kipz] + f2*hxp[2] + f3*h[2];
1077 vout[kipx] = vect[kipx] + f4*vect[kipx] + f5*hxp[0] + f6*h[0];
1078 vout[kipy] = vect[kipy] + f4*vect[kipy] + f5*hxp[1] + f6*h[1];
1079 vout[kipz] = vect[kipz] + f4*vect[kipz] + f5*hxp[2] + f6*h[2];
1084 //__________________________________________________________________________
1085 void AliMUONTrackExtrap::ExtrapOneStepHelix3(Double_t field, Double_t step, Double_t *vect, Double_t *vout)
1088 /// ******************************************************************
1090 /// * Tracking routine in a constant field oriented *
1091 /// * along axis 3 *
1092 /// * Tracking is performed with a conventional *
1093 /// * helix step method *
1095 /// * ==>Called by : USER, GUSWIM *
1096 /// * Authors R.Brun, M.Hansroul ********* *
1097 /// * Rewritten V.Perevoztchikov
1099 /// ******************************************************************
1103 Double_t h4, hp, rho, tet;
1104 Double_t sint, sintt, tsint, cos1t;
1105 Double_t f1, f2, f3, f4, f5, f6;
1107 const Int_t kix = 0;
1108 const Int_t kiy = 1;
1109 const Int_t kiz = 2;
1110 const Int_t kipx = 3;
1111 const Int_t kipy = 4;
1112 const Int_t kipz = 5;
1113 const Int_t kipp = 6;
1115 const Double_t kec = 2.9979251e-4;
1118 // ------------------------------------------------------------------
1120 // units are kgauss,centimeters,gev/c
1122 vout[kipp] = vect[kipp];
1125 hxp[0] = - vect[kipy];
1126 hxp[1] = + vect[kipx];
1130 rho = -h4/vect[kipp];
1132 if (TMath::Abs(tet) > 0.15) {
1133 sint = TMath::Sin(tet);
1135 tsint = (tet-sint)/tet;
1136 cos1t = 2.* TMath::Sin(0.5*tet) * TMath::Sin(0.5*tet)/tet;
1138 tsint = tet*tet/36.;
1139 sintt = (1. - tsint);
1146 f3 = step * tsint * hp;
1149 f6 = tet * cos1t * hp;
1151 vout[kix] = vect[kix] + f1*vect[kipx] + f2*hxp[0];
1152 vout[kiy] = vect[kiy] + f1*vect[kipy] + f2*hxp[1];
1153 vout[kiz] = vect[kiz] + f1*vect[kipz] + f3;
1155 vout[kipx] = vect[kipx] + f4*vect[kipx] + f5*hxp[0];
1156 vout[kipy] = vect[kipy] + f4*vect[kipy] + f5*hxp[1];
1157 vout[kipz] = vect[kipz] + f4*vect[kipz] + f6;
1162 //__________________________________________________________________________
1163 void AliMUONTrackExtrap::ExtrapOneStepRungekutta(Double_t charge, Double_t step, Double_t* vect, Double_t* vout)
1166 /// ******************************************************************
1168 /// * Runge-Kutta method for tracking a particle through a magnetic *
1169 /// * field. Uses Nystroem algorithm (See Handbook Nat. Bur. of *
1170 /// * Standards, procedure 25.5.20) *
1172 /// * Input parameters *
1173 /// * CHARGE Particle charge *
1174 /// * STEP Step size *
1175 /// * VECT Initial co-ords,direction cosines,momentum *
1176 /// * Output parameters *
1177 /// * VOUT Output co-ords,direction cosines,momentum *
1178 /// * User routine called *
1179 /// * CALL GUFLD(X,F) *
1181 /// * ==>Called by : USER, GUSWIM *
1182 /// * Authors R.Brun, M.Hansroul ********* *
1183 /// * V.Perevoztchikov (CUT STEP implementation) *
1186 /// ******************************************************************
1189 Double_t h2, h4, f[4];
1190 Double_t xyzt[3], a, b, c, ph,ph2;
1191 Double_t secxs[4],secys[4],seczs[4],hxp[3];
1192 Double_t g1, g2, g3, g4, g5, g6, ang2, dxt, dyt, dzt;
1193 Double_t est, at, bt, ct, cba;
1194 Double_t f1, f2, f3, f4, rho, tet, hnorm, hp, rho1, sint, cost;
1204 Double_t maxit = 1992;
1205 Double_t maxcut = 11;
1207 const Double_t kdlt = 1e-4;
1208 const Double_t kdlt32 = kdlt/32.;
1209 const Double_t kthird = 1./3.;
1210 const Double_t khalf = 0.5;
1211 const Double_t kec = 2.9979251e-4;
1213 const Double_t kpisqua = 9.86960440109;
1214 const Int_t kix = 0;
1215 const Int_t kiy = 1;
1216 const Int_t kiz = 2;
1217 const Int_t kipx = 3;
1218 const Int_t kipy = 4;
1219 const Int_t kipz = 5;
1222 // *. ------------------------------------------------------------------
1224 // * this constant is for units cm,gev/c and kgauss
1228 for(Int_t j = 0; j < 7; j++)
1231 Double_t pinv = kec * charge / vect[6];
1239 if (TMath::Abs(h) > TMath::Abs(rest)) h = rest;
1240 //cmodif: call gufld(vout,f) changed into:
1241 TGeoGlobalMagField::Instance()->Field(vout,f);
1244 // * start of integration
1257 secxs[0] = (b * f[2] - c * f[1]) * ph2;
1258 secys[0] = (c * f[0] - a * f[2]) * ph2;
1259 seczs[0] = (a * f[1] - b * f[0]) * ph2;
1260 ang2 = (secxs[0]*secxs[0] + secys[0]*secys[0] + seczs[0]*seczs[0]);
1261 if (ang2 > kpisqua) break;
1263 dxt = h2 * a + h4 * secxs[0];
1264 dyt = h2 * b + h4 * secys[0];
1265 dzt = h2 * c + h4 * seczs[0];
1270 // * second intermediate point
1273 est = TMath::Abs(dxt) + TMath::Abs(dyt) + TMath::Abs(dzt);
1275 if (ncut++ > maxcut) break;
1284 //cmodif: call gufld(xyzt,f) changed into:
1285 TGeoGlobalMagField::Instance()->Field(xyzt,f);
1291 secxs[1] = (bt * f[2] - ct * f[1]) * ph2;
1292 secys[1] = (ct * f[0] - at * f[2]) * ph2;
1293 seczs[1] = (at * f[1] - bt * f[0]) * ph2;
1297 secxs[2] = (bt * f[2] - ct * f[1]) * ph2;
1298 secys[2] = (ct * f[0] - at * f[2]) * ph2;
1299 seczs[2] = (at * f[1] - bt * f[0]) * ph2;
1300 dxt = h * (a + secxs[2]);
1301 dyt = h * (b + secys[2]);
1302 dzt = h * (c + seczs[2]);
1306 at = a + 2.*secxs[2];
1307 bt = b + 2.*secys[2];
1308 ct = c + 2.*seczs[2];
1310 est = TMath::Abs(dxt)+TMath::Abs(dyt)+TMath::Abs(dzt);
1311 if (est > 2.*TMath::Abs(h)) {
1312 if (ncut++ > maxcut) break;
1321 //cmodif: call gufld(xyzt,f) changed into:
1322 TGeoGlobalMagField::Instance()->Field(xyzt,f);
1324 z = z + (c + (seczs[0] + seczs[1] + seczs[2]) * kthird) * h;
1325 y = y + (b + (secys[0] + secys[1] + secys[2]) * kthird) * h;
1326 x = x + (a + (secxs[0] + secxs[1] + secxs[2]) * kthird) * h;
1328 secxs[3] = (bt*f[2] - ct*f[1])* ph2;
1329 secys[3] = (ct*f[0] - at*f[2])* ph2;
1330 seczs[3] = (at*f[1] - bt*f[0])* ph2;
1331 a = a+(secxs[0]+secxs[3]+2. * (secxs[1]+secxs[2])) * kthird;
1332 b = b+(secys[0]+secys[3]+2. * (secys[1]+secys[2])) * kthird;
1333 c = c+(seczs[0]+seczs[3]+2. * (seczs[1]+seczs[2])) * kthird;
1335 est = TMath::Abs(secxs[0]+secxs[3] - (secxs[1]+secxs[2]))
1336 + TMath::Abs(secys[0]+secys[3] - (secys[1]+secys[2]))
1337 + TMath::Abs(seczs[0]+seczs[3] - (seczs[1]+seczs[2]));
1339 if (est > kdlt && TMath::Abs(h) > 1.e-4) {
1340 if (ncut++ > maxcut) break;
1346 // * if too many iterations, go to helix
1347 if (iter++ > maxit) break;
1352 cba = 1./ TMath::Sqrt(a*a + b*b + c*c);
1360 if (step < 0.) rest = -rest;
1361 if (rest < 1.e-5*TMath::Abs(step)) return;
1365 // angle too big, use helix
1370 f4 = TMath::Sqrt(f1*f1+f2*f2+f3*f3);
1379 hxp[0] = f2*vect[kipz] - f3*vect[kipy];
1380 hxp[1] = f3*vect[kipx] - f1*vect[kipz];
1381 hxp[2] = f1*vect[kipy] - f2*vect[kipx];
1383 hp = f1*vect[kipx] + f2*vect[kipy] + f3*vect[kipz];
1386 sint = TMath::Sin(tet);
1387 cost = 2.*TMath::Sin(khalf*tet)*TMath::Sin(khalf*tet);
1391 g3 = (tet-sint) * hp*rho1;
1396 vout[kix] = vect[kix] + g1*vect[kipx] + g2*hxp[0] + g3*f1;
1397 vout[kiy] = vect[kiy] + g1*vect[kipy] + g2*hxp[1] + g3*f2;
1398 vout[kiz] = vect[kiz] + g1*vect[kipz] + g2*hxp[2] + g3*f3;
1400 vout[kipx] = vect[kipx] + g4*vect[kipx] + g5*hxp[0] + g6*f1;
1401 vout[kipy] = vect[kipy] + g4*vect[kipy] + g5*hxp[1] + g6*f2;
1402 vout[kipz] = vect[kipz] + g4*vect[kipz] + g5*hxp[2] + g6*f3;