- Compute parameter covariances including absorber dispersion effects
[u/mrichter/AliRoot.git] / MUON / AliMUONTrackExtrap.cxx
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c04e3238 1/**************************************************************************
2 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
3 * *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
6 * *
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 **************************************************************************/
15
16/* $Id$ */
17
56316147 18//-----------------------------------------------------------------------------
19// Class AliMUONTrackExtrap
20// ------------------------
21// Tools for track extrapolation in ALICE dimuon spectrometer
22// Author: Philippe Pillot
23//-----------------------------------------------------------------------------
c04e3238 24
c04e3238 25#include "AliMUONTrackExtrap.h"
26#include "AliMUONTrackParam.h"
27#include "AliMUONConstants.h"
8cde4af5 28
c04e3238 29#include "AliMagF.h"
8cde4af5 30
8cde4af5 31#include <TMath.h>
8cde4af5 32#include <TGeoManager.h>
c04e3238 33
ea94c18b 34#include <Riostream.h>
35
78649106 36/// \cond CLASSIMP
c04e3238 37ClassImp(AliMUONTrackExtrap) // Class implementation in ROOT context
78649106 38/// \endcond
c04e3238 39
40const AliMagF* AliMUONTrackExtrap::fgkField = 0x0;
4284483e 41const Bool_t AliMUONTrackExtrap::fgkUseHelix = kFALSE;
208f139e 42const Int_t AliMUONTrackExtrap::fgkMaxStepNumber = 5000;
4284483e 43const Double_t AliMUONTrackExtrap::fgkHelixStepLength = 6.;
44const Double_t AliMUONTrackExtrap::fgkRungeKuttaMaxResidue = 0.002;
208f139e 45
690d2205 46//__________________________________________________________________________
208f139e 47Double_t AliMUONTrackExtrap::GetImpactParamFromBendingMomentum(Double_t bendingMomentum)
48{
49 /// Returns impact parameter at vertex in bending plane (cm),
50 /// from the signed bending momentum "BendingMomentum" in bending plane (GeV/c),
51 /// using simple values for dipole magnetic field.
52 /// The sign of "BendingMomentum" is the sign of the charge.
53
54 if (bendingMomentum == 0.) return 1.e10;
55
56 Double_t simpleBPosition = 0.5 * (AliMUONConstants::CoilZ() + AliMUONConstants::YokeZ());
57 Double_t simpleBLength = 0.5 * (AliMUONConstants::CoilL() + AliMUONConstants::YokeL());
58 Float_t b[3], x[3] = {0.,0.,(Float_t) simpleBPosition};
59 if (fgkField) fgkField->Field(x,b);
60 else {
61 cout<<"F-AliMUONTrackExtrap::GetField: fgkField = 0x0"<<endl;
62 exit(-1);
63 }
64 Double_t simpleBValue = (Double_t) b[0];
65
66 return (-0.0003 * simpleBValue * simpleBLength * simpleBPosition / bendingMomentum);
67}
68
690d2205 69//__________________________________________________________________________
208f139e 70Double_t AliMUONTrackExtrap::GetBendingMomentumFromImpactParam(Double_t impactParam)
71{
72 /// Returns signed bending momentum in bending plane (GeV/c),
73 /// the sign being the sign of the charge for particles moving forward in Z,
74 /// from the impact parameter "ImpactParam" at vertex in bending plane (cm),
75 /// using simple values for dipole magnetic field.
76
77 if (impactParam == 0.) return 1.e10;
78
79 Double_t simpleBPosition = 0.5 * (AliMUONConstants::CoilZ() + AliMUONConstants::YokeZ());
80 Double_t simpleBLength = 0.5 * (AliMUONConstants::CoilL() + AliMUONConstants::YokeL());
81 Float_t b[3], x[3] = {0.,0.,(Float_t) simpleBPosition};
82 if (fgkField) fgkField->Field(x,b);
83 else {
84 cout<<"F-AliMUONTrackExtrap::GetField: fgkField = 0x0"<<endl;
85 exit(-1);
86 }
87 Double_t simpleBValue = (Double_t) b[0];
88
89 return (-0.0003 * simpleBValue * simpleBLength * simpleBPosition / impactParam);
019df241 90}
91
690d2205 92//__________________________________________________________________________
019df241 93void AliMUONTrackExtrap::LinearExtrapToZ(AliMUONTrackParam* trackParam, Double_t zEnd)
94{
95 /// Track parameters (and their covariances if any) linearly extrapolated to the plane at "zEnd".
96 /// On return, results from the extrapolation are updated in trackParam.
97
98 if (trackParam->GetZ() == zEnd) return; // nothing to be done if same z
99
100 // Compute track parameters
101 Double_t dZ = zEnd - trackParam->GetZ();
102 trackParam->SetNonBendingCoor(trackParam->GetNonBendingCoor() + trackParam->GetNonBendingSlope() * dZ);
103 trackParam->SetBendingCoor(trackParam->GetBendingCoor() + trackParam->GetBendingSlope() * dZ);
104 trackParam->SetZ(zEnd);
105
106 // Update track parameters covariances if any
107 if (trackParam->CovariancesExist()) {
108 TMatrixD paramCov(trackParam->GetCovariances());
109 paramCov(0,0) += dZ * dZ * paramCov(1,1) + 2. * dZ * paramCov(0,1);
110 paramCov(0,1) += dZ * paramCov(1,1);
111 paramCov(1,0) = paramCov(0,1);
112 paramCov(2,2) += dZ * dZ * paramCov(3,3) + 2. * dZ * paramCov(2,3);
113 paramCov(2,3) += dZ * paramCov(3,3);
114 paramCov(3,2) = paramCov(2,3);
115 trackParam->SetCovariances(paramCov);
116 }
117
208f139e 118}
c04e3238 119
690d2205 120//__________________________________________________________________________
c04e3238 121void AliMUONTrackExtrap::ExtrapToZ(AliMUONTrackParam* trackParam, Double_t zEnd)
122{
4284483e 123 /// Interface to track parameter extrapolation to the plane at "Z" using Helix or Rungekutta algorithm.
124 /// On return, the track parameters resulting from the extrapolation are updated in trackParam.
125 if (fgkUseHelix) AliMUONTrackExtrap::ExtrapToZHelix(trackParam,zEnd);
126 else AliMUONTrackExtrap::ExtrapToZRungekutta(trackParam,zEnd);
127}
128
690d2205 129//__________________________________________________________________________
4284483e 130void AliMUONTrackExtrap::ExtrapToZHelix(AliMUONTrackParam* trackParam, Double_t zEnd)
131{
132 /// Track parameter extrapolation to the plane at "Z" using Helix algorithm.
c04e3238 133 /// On return, the track parameters resulting from the extrapolation are updated in trackParam.
134 if (trackParam->GetZ() == zEnd) return; // nothing to be done if same Z
135 Double_t forwardBackward; // +1 if forward, -1 if backward
136 if (zEnd < trackParam->GetZ()) forwardBackward = 1.0; // spectro. z<0
137 else forwardBackward = -1.0;
dade8580 138 Double_t v3[7], v3New[7]; // 7 in parameter ????
139 Int_t i3, stepNumber;
c04e3238 140 // For safety: return kTRUE or kFALSE ????
141 // Parameter vector for calling EXTRAP_ONESTEP
4284483e 142 ConvertTrackParamForExtrap(trackParam, forwardBackward, v3);
c04e3238 143 // sign of charge (sign of fInverseBendingMomentum if forward motion)
144 // must be changed if backward extrapolation
208f139e 145 Double_t chargeExtrap = forwardBackward * TMath::Sign(Double_t(1.0), trackParam->GetInverseBendingMomentum());
c04e3238 146 // Extrapolation loop
147 stepNumber = 0;
208f139e 148 while (((-forwardBackward * (v3[2] - zEnd)) <= 0.0) && (stepNumber < fgkMaxStepNumber)) { // spectro. z<0
c04e3238 149 stepNumber++;
4284483e 150 ExtrapOneStepHelix(chargeExtrap, fgkHelixStepLength, v3, v3New);
dade8580 151 if ((-forwardBackward * (v3New[2] - zEnd)) > 0.0) break; // one is beyond Z spectro. z<0
690d2205 152 // better use TArray ????
208f139e 153 for (i3 = 0; i3 < 7; i3++) {v3[i3] = v3New[i3];}
c04e3238 154 }
208f139e 155 // check fgkMaxStepNumber ????
c04e3238 156 // Interpolation back to exact Z (2nd order)
157 // should be in function ???? using TArray ????
dade8580 158 Double_t dZ12 = v3New[2] - v3[2]; // 1->2
c04e3238 159 if (TMath::Abs(dZ12) > 0) {
dade8580 160 Double_t dZ1i = zEnd - v3[2]; // 1-i
161 Double_t dZi2 = v3New[2] - zEnd; // i->2
162 Double_t xPrime = (v3New[0] - v3[0]) / dZ12;
163 Double_t xSecond = ((v3New[3] / v3New[5]) - (v3[3] / v3[5])) / dZ12;
164 Double_t yPrime = (v3New[1] - v3[1]) / dZ12;
165 Double_t ySecond = ((v3New[4] / v3New[5]) - (v3[4] / v3[5])) / dZ12;
166 v3[0] = v3[0] + xPrime * dZ1i - 0.5 * xSecond * dZ1i * dZi2; // X
167 v3[1] = v3[1] + yPrime * dZ1i - 0.5 * ySecond * dZ1i * dZi2; // Y
168 v3[2] = zEnd; // Z
c04e3238 169 Double_t xPrimeI = xPrime - 0.5 * xSecond * (dZi2 - dZ1i);
170 Double_t yPrimeI = yPrime - 0.5 * ySecond * (dZi2 - dZ1i);
171 // (PX, PY, PZ)/PTOT assuming forward motion
208f139e 172 v3[5] = 1.0 / TMath::Sqrt(1.0 + xPrimeI * xPrimeI + yPrimeI * yPrimeI); // PZ/PTOT
dade8580 173 v3[3] = xPrimeI * v3[5]; // PX/PTOT
174 v3[4] = yPrimeI * v3[5]; // PY/PTOT
c04e3238 175 } else {
4284483e 176 cout<<"W-AliMUONTrackExtrap::ExtrapToZHelix: Extrap. to Z not reached, Z = "<<zEnd<<endl;
c04e3238 177 }
4284483e 178 // Recover track parameters (charge back for forward motion)
dade8580 179 RecoverTrackParam(v3, chargeExtrap * forwardBackward, trackParam);
c04e3238 180}
181
690d2205 182//__________________________________________________________________________
4284483e 183void AliMUONTrackExtrap::ExtrapToZRungekutta(AliMUONTrackParam* trackParam, Double_t zEnd)
184{
185 /// Track parameter extrapolation to the plane at "Z" using Rungekutta algorithm.
186 /// On return, the track parameters resulting from the extrapolation are updated in trackParam.
187 if (trackParam->GetZ() == zEnd) return; // nothing to be done if same Z
188 Double_t forwardBackward; // +1 if forward, -1 if backward
189 if (zEnd < trackParam->GetZ()) forwardBackward = 1.0; // spectro. z<0
190 else forwardBackward = -1.0;
191 // sign of charge (sign of fInverseBendingMomentum if forward motion)
192 // must be changed if backward extrapolation
193 Double_t chargeExtrap = forwardBackward * TMath::Sign(Double_t(1.0), trackParam->GetInverseBendingMomentum());
194 Double_t v3[7], v3New[7];
195 Double_t dZ, step;
196 Int_t stepNumber = 0;
197
198 // Extrapolation loop (until within tolerance)
199 Double_t residue = zEnd - trackParam->GetZ();
200 while (TMath::Abs(residue) > fgkRungeKuttaMaxResidue && stepNumber <= fgkMaxStepNumber) {
201 dZ = zEnd - trackParam->GetZ();
202 // step lenght assuming linear trajectory
203 step = dZ * TMath::Sqrt(1.0 + trackParam->GetBendingSlope()*trackParam->GetBendingSlope() +
690d2205 204 trackParam->GetNonBendingSlope()*trackParam->GetNonBendingSlope());
4284483e 205 ConvertTrackParamForExtrap(trackParam, forwardBackward, v3);
206 do { // reduce step lenght while zEnd oversteped
207 if (stepNumber > fgkMaxStepNumber) {
208 cout<<"W-AliMUONTrackExtrap::ExtrapToZRungekutta: Too many trials: "<<stepNumber<<endl;
209 break;
210 }
211 stepNumber ++;
212 step = TMath::Abs(step);
213 AliMUONTrackExtrap::ExtrapOneStepRungekutta(chargeExtrap,step,v3,v3New);
214 residue = zEnd - v3New[2];
215 step *= dZ/(v3New[2]-trackParam->GetZ());
216 } while (residue*dZ < 0 && TMath::Abs(residue) > fgkRungeKuttaMaxResidue);
217 RecoverTrackParam(v3New, chargeExtrap * forwardBackward, trackParam);
218 }
219
220 // terminate the extropolation with a straight line up to the exact "zEnd" value
221 trackParam->SetNonBendingCoor(trackParam->GetNonBendingCoor() + residue * trackParam->GetNonBendingSlope());
222 trackParam->SetBendingCoor(trackParam->GetBendingCoor() + residue * trackParam->GetBendingSlope());
223 trackParam->SetZ(zEnd);
224}
225
690d2205 226//__________________________________________________________________________
4284483e 227void AliMUONTrackExtrap::ConvertTrackParamForExtrap(AliMUONTrackParam* trackParam, Double_t forwardBackward, Double_t *v3)
c04e3238 228{
dade8580 229 /// Set vector of Geant3 parameters pointed to by "v3" from track parameters in trackParam.
c04e3238 230 /// Since AliMUONTrackParam is only geometry, one uses "forwardBackward"
231 /// to know whether the particle is going forward (+1) or backward (-1).
dade8580 232 v3[0] = trackParam->GetNonBendingCoor(); // X
233 v3[1] = trackParam->GetBendingCoor(); // Y
234 v3[2] = trackParam->GetZ(); // Z
c04e3238 235 Double_t pYZ = TMath::Abs(1.0 / trackParam->GetInverseBendingMomentum());
236 Double_t pZ = pYZ / TMath::Sqrt(1.0 + trackParam->GetBendingSlope() * trackParam->GetBendingSlope());
dade8580 237 v3[6] = TMath::Sqrt(pYZ * pYZ + pZ * pZ * trackParam->GetNonBendingSlope() * trackParam->GetNonBendingSlope()); // PTOT
238 v3[5] = -forwardBackward * pZ / v3[6]; // PZ/PTOT spectro. z<0
239 v3[3] = trackParam->GetNonBendingSlope() * v3[5]; // PX/PTOT
240 v3[4] = trackParam->GetBendingSlope() * v3[5]; // PY/PTOT
c04e3238 241}
242
690d2205 243//__________________________________________________________________________
dade8580 244void AliMUONTrackExtrap::RecoverTrackParam(Double_t *v3, Double_t charge, AliMUONTrackParam* trackParam)
c04e3238 245{
dade8580 246 /// Set track parameters in trackParam from Geant3 parameters pointed to by "v3",
c04e3238 247 /// assumed to be calculated for forward motion in Z.
248 /// "InverseBendingMomentum" is signed with "charge".
dade8580 249 trackParam->SetNonBendingCoor(v3[0]); // X
250 trackParam->SetBendingCoor(v3[1]); // Y
251 trackParam->SetZ(v3[2]); // Z
252 Double_t pYZ = v3[6] * TMath::Sqrt(1.0 - v3[3] * v3[3]);
c04e3238 253 trackParam->SetInverseBendingMomentum(charge/pYZ);
dade8580 254 trackParam->SetBendingSlope(v3[4]/v3[5]);
255 trackParam->SetNonBendingSlope(v3[3]/v3[5]);
208f139e 256}
257
690d2205 258//__________________________________________________________________________
ea94c18b 259void AliMUONTrackExtrap::ExtrapToZCov(AliMUONTrackParam* trackParam, Double_t zEnd, Bool_t updatePropagator)
208f139e 260{
261 /// Track parameters and their covariances extrapolated to the plane at "zEnd".
262 /// On return, results from the extrapolation are updated in trackParam.
263
264 if (trackParam->GetZ() == zEnd) return; // nothing to be done if same z
265
ea94c18b 266 // No need to propagate the covariance matrix if it does not exist
267 if (!trackParam->CovariancesExist()) {
268 cout<<"W-AliMUONTrackExtrap::ExtrapToZCov: Covariance matrix does not exist"<<endl;
269 // Extrapolate track parameters to "zEnd"
270 ExtrapToZ(trackParam,zEnd);
271 return;
272 }
273
208f139e 274 // Save the actual track parameters
275 AliMUONTrackParam trackParamSave(*trackParam);
ea94c18b 276 TMatrixD paramSave(trackParamSave.GetParameters());
277 Double_t zBegin = trackParamSave.GetZ();
278
279 // Get reference to the parameter covariance matrix
280 const TMatrixD& kParamCov = trackParam->GetCovariances();
208f139e 281
282 // Extrapolate track parameters to "zEnd"
283 ExtrapToZ(trackParam,zEnd);
208f139e 284
ea94c18b 285 // Get reference to the extrapolated parameters
286 const TMatrixD& extrapParam = trackParam->GetParameters();
208f139e 287
288 // Calculate the jacobian related to the track parameters extrapolation to "zEnd"
289 TMatrixD jacob(5,5);
ea94c18b 290 jacob.Zero();
291 TMatrixD dParam(5,1);
208f139e 292 for (Int_t i=0; i<5; i++) {
293 // Skip jacobian calculation for parameters with no associated error
ea94c18b 294 if (kParamCov(i,i) == 0.) continue;
295
208f139e 296 // Small variation of parameter i only
297 for (Int_t j=0; j<5; j++) {
298 if (j==i) {
ea94c18b 299 dParam(j,0) = TMath::Sqrt(kParamCov(i,i));
300 if (j == 4) dParam(j,0) *= TMath::Sign(1.,-paramSave(4,0)); // variation always in the same direction
301 } else dParam(j,0) = 0.;
208f139e 302 }
ea94c18b 303
208f139e 304 // Set new parameters
ea94c18b 305 trackParamSave.SetParameters(paramSave);
306 trackParamSave.AddParameters(dParam);
307 trackParamSave.SetZ(zBegin);
308
208f139e 309 // Extrapolate new track parameters to "zEnd"
310 ExtrapToZ(&trackParamSave,zEnd);
ea94c18b 311
208f139e 312 // Calculate the jacobian
ea94c18b 313 TMatrixD jacobji(trackParamSave.GetParameters(),TMatrixD::kMinus,extrapParam);
314 jacobji *= 1. / dParam(i,0);
315 jacob.SetSub(0,i,jacobji);
208f139e 316 }
317
318 // Extrapolate track parameter covariances to "zEnd"
ea94c18b 319 TMatrixD tmp(kParamCov,TMatrixD::kMultTranspose,jacob);
320 TMatrixD tmp2(jacob,TMatrixD::kMult,tmp);
321 trackParam->SetCovariances(tmp2);
322
323 // Update the propagator if required
324 if (updatePropagator) trackParam->UpdatePropagator(jacob);
208f139e 325}
326
690d2205 327//__________________________________________________________________________
8cde4af5 328void AliMUONTrackExtrap::AddMCSEffectInAbsorber(AliMUONTrackParam* param, Double_t pathLength, Double_t f0, Double_t f1, Double_t f2)
329{
330 /// Add to the track parameter covariances the effects of multiple Coulomb scattering
690d2205 331 /// The absorber correction parameters are supposed to be calculated at the current track z-position
8cde4af5 332
333 // absorber related covariance parameters
334 Double_t bendingSlope = param->GetBendingSlope();
335 Double_t nonBendingSlope = param->GetNonBendingSlope();
336 Double_t inverseBendingMomentum = param->GetInverseBendingMomentum();
337 Double_t alpha2 = 0.0136 * 0.0136 * inverseBendingMomentum * inverseBendingMomentum * (1.0 + bendingSlope * bendingSlope) /
690d2205 338 (1.0 + bendingSlope *bendingSlope + nonBendingSlope * nonBendingSlope); // velocity = 1
8cde4af5 339 Double_t varCoor = alpha2 * (pathLength * pathLength * f0 - 2. * pathLength * f1 + f2);
340 Double_t covCorrSlope = alpha2 * (pathLength * f0 - f1);
341 Double_t varSlop = alpha2 * f0;
342
690d2205 343 // compute derivative d(q/Pxy) / dSlopeX and d(q/Pxy) / dSlopeX
344 Double_t dqPxydSlopeX = inverseBendingMomentum * nonBendingSlope / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
345 Double_t dqPxydSlopeY = - inverseBendingMomentum * nonBendingSlope*nonBendingSlope * bendingSlope /
346 (1. + bendingSlope*bendingSlope) / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
347
348 // Set MCS covariance matrix
ea94c18b 349 TMatrixD newParamCov(param->GetCovariances());
8cde4af5 350 // Non bending plane
ea94c18b 351 newParamCov(0,0) += varCoor; newParamCov(0,1) += covCorrSlope;
352 newParamCov(1,0) += covCorrSlope; newParamCov(1,1) += varSlop;
8cde4af5 353 // Bending plane
ea94c18b 354 newParamCov(2,2) += varCoor; newParamCov(2,3) += covCorrSlope;
355 newParamCov(3,2) += covCorrSlope; newParamCov(3,3) += varSlop;
690d2205 356 // Inverse bending momentum (due to dependences with bending and non bending slopes)
357 newParamCov(4,0) += dqPxydSlopeX * covCorrSlope; newParamCov(0,4) += dqPxydSlopeX * covCorrSlope;
358 newParamCov(4,1) += dqPxydSlopeX * varSlop; newParamCov(1,4) += dqPxydSlopeX * varSlop;
359 newParamCov(4,2) += dqPxydSlopeY * covCorrSlope; newParamCov(2,4) += dqPxydSlopeY * covCorrSlope;
360 newParamCov(4,3) += dqPxydSlopeY * varSlop; newParamCov(3,4) += dqPxydSlopeY * varSlop;
361 newParamCov(4,4) += (dqPxydSlopeX*dqPxydSlopeX + dqPxydSlopeY*dqPxydSlopeY) * varSlop;
ea94c18b 362
363 // Set new covariances
364 param->SetCovariances(newParamCov);
690d2205 365}
366
367//__________________________________________________________________________
368void AliMUONTrackExtrap::CorrectMCSEffectInAbsorber(AliMUONTrackParam* param,
369 Double_t xVtx, Double_t yVtx, Double_t zVtx,
370 Double_t errXVtx, Double_t errYVtx,
371 Double_t absZBeg, Double_t pathLength, Double_t f0, Double_t f1, Double_t f2)
372{
373 /// Correct parameters and corresponding covariances using Branson correction
374 /// - input param are parameters and covariances at the end of absorber
375 /// - output param are parameters and covariances at vertex
376 /// Absorber correction parameters are supposed to be calculated at the current track z-position
377
378 // Position of the Branson plane (spectro. (z<0))
379 Double_t zB = (f1>0.) ? absZBeg - f2/f1 : 0.;
380
381 // Add MCS effects to current parameter covariances
382 AddMCSEffectInAbsorber(param, pathLength, f0, f1, f2);
383
384 // Get track parameters and covariances in the Branson plane corrected for magnetic field effect
385 ExtrapToZCov(param,zVtx);
386 LinearExtrapToZ(param,zB);
387
388 // compute track parameters at vertex
389 TMatrixD newParam(5,1);
390 newParam(0,0) = xVtx;
391 newParam(1,0) = (param->GetNonBendingCoor() - xVtx) / (zB - zVtx);
392 newParam(2,0) = yVtx;
393 newParam(3,0) = (param->GetBendingCoor() - yVtx) / (zB - zVtx);
394 newParam(4,0) = param->GetCharge() / param->P() *
395 TMath::Sqrt(1.0 + newParam(1,0)*newParam(1,0) + newParam(3,0)*newParam(3,0)) /
396 TMath::Sqrt(1.0 + newParam(3,0)*newParam(3,0));
397
398 // Get covariances in (X, SlopeX, Y, SlopeY, q*PTot) coordinate system
399 TMatrixD paramCovP(param->GetCovariances());
400 Cov2CovP(param->GetParameters(),paramCovP);
401
402 // Get the covariance matrix in the (XVtx, X, YVtx, Y, q*PTot) coordinate system
403 TMatrixD paramCovVtx(5,5);
404 paramCovVtx.Zero();
405 paramCovVtx(0,0) = errXVtx * errXVtx;
406 paramCovVtx(1,1) = paramCovP(0,0);
407 paramCovVtx(2,2) = errYVtx * errYVtx;
408 paramCovVtx(3,3) = paramCovP(2,2);
409 paramCovVtx(4,4) = paramCovP(4,4);
410 paramCovVtx(1,3) = paramCovP(0,2);
411 paramCovVtx(3,1) = paramCovP(2,0);
412 paramCovVtx(1,4) = paramCovP(0,4);
413 paramCovVtx(4,1) = paramCovP(4,0);
414 paramCovVtx(3,4) = paramCovP(2,4);
415 paramCovVtx(4,3) = paramCovP(4,2);
416
417 // Jacobian of the transformation (XVtx, X, YVtx, Y, q*PTot) -> (XVtx, SlopeXVtx, YVtx, SlopeYVtx, q*PTotVtx)
418 TMatrixD jacob(5,5);
419 jacob.UnitMatrix();
420 jacob(1,0) = - 1. / (zB - zVtx);
421 jacob(1,1) = 1. / (zB - zVtx);
422 jacob(3,2) = - 1. / (zB - zVtx);
423 jacob(3,3) = 1. / (zB - zVtx);
8cde4af5 424
690d2205 425 // Compute covariances at vertex in the (XVtx, SlopeXVtx, YVtx, SlopeYVtx, q*PTotVtx) coordinate system
426 TMatrixD tmp(paramCovVtx,TMatrixD::kMultTranspose,jacob);
427 TMatrixD newParamCov(jacob,TMatrixD::kMult,tmp);
428
429 // Compute covariances at vertex in the (XVtx, SlopeXVtx, YVtx, SlopeYVtx, q/PyzVtx) coordinate system
430 CovP2Cov(newParam,newParamCov);
431
432 // Set parameters and covariances at vertex
433 param->SetParameters(newParam);
434 param->SetZ(zVtx);
435 param->SetCovariances(newParamCov);
8cde4af5 436}
437
690d2205 438//__________________________________________________________________________
439void AliMUONTrackExtrap::CorrectELossEffectInAbsorber(AliMUONTrackParam* param, Double_t eLoss, Double_t sigmaELoss2)
440{
441 /// Correct parameters for energy loss and add energy loss fluctuation effect to covariances
442
443 // Get parameter covariances in (X, SlopeX, Y, SlopeY, q*PTot) coordinate system
444 TMatrixD newParamCov(param->GetCovariances());
445 Cov2CovP(param->GetParameters(),newParamCov);
446
447 // Add effects of energy loss fluctuation to covariances
448 newParamCov(4,4) += sigmaELoss2;
449
450 // Compute new parameters corrected for energy loss
451 Double_t nonBendingSlope = param->GetNonBendingSlope();
452 Double_t bendingSlope = param->GetBendingSlope();
453 param->SetInverseBendingMomentum(param->GetCharge() / (param->P() + eLoss) *
454 TMath::Sqrt(1.0 + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope) /
455 TMath::Sqrt(1.0 + bendingSlope*bendingSlope));
456
457 // Get new parameter covariances in (X, SlopeX, Y, SlopeY, q/Pyz) coordinate system
458 CovP2Cov(param->GetParameters(),newParamCov);
459
460 // Set new parameter covariances
461 param->SetCovariances(newParamCov);
462}
463
464//__________________________________________________________________________
465void AliMUONTrackExtrap::GetAbsorberCorrectionParam(Double_t trackXYZIn[3], Double_t trackXYZOut[3], Double_t pTotal,
466 Double_t &pathLength, Double_t &f0, Double_t &f1, Double_t &f2,
467 Double_t &meanRho, Double_t &totalELoss, Double_t &sigmaELoss2)
8cde4af5 468{
469 /// Parameters used to correct for Multiple Coulomb Scattering and energy loss in absorber
690d2205 470 /// Calculated assuming a linear propagation from trackXYZIn to trackXYZOut (order is important)
8cde4af5 471 // pathLength: path length between trackXYZIn and trackXYZOut (cm)
472 // f0: 0th moment of z calculated with the inverse radiation-length distribution
473 // f1: 1st moment of z calculated with the inverse radiation-length distribution
474 // f2: 2nd moment of z calculated with the inverse radiation-length distribution
475 // meanRho: average density of crossed material (g/cm3)
84f061ef 476 // totalELoss: total energy loss in absorber
8cde4af5 477
478 // Reset absorber's parameters
479 pathLength = 0.;
480 f0 = 0.;
481 f1 = 0.;
482 f2 = 0.;
483 meanRho = 0.;
84f061ef 484 totalELoss = 0.;
690d2205 485 sigmaELoss2 = 0.;
8cde4af5 486
487 // Check whether the geometry is available
488 if (!gGeoManager) {
489 cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: no TGeo"<<endl;
490 return;
491 }
492
493 // Initialize starting point and direction
494 pathLength = TMath::Sqrt((trackXYZOut[0] - trackXYZIn[0])*(trackXYZOut[0] - trackXYZIn[0])+
495 (trackXYZOut[1] - trackXYZIn[1])*(trackXYZOut[1] - trackXYZIn[1])+
496 (trackXYZOut[2] - trackXYZIn[2])*(trackXYZOut[2] - trackXYZIn[2]));
497 if (pathLength < TGeoShape::Tolerance()) return;
498 Double_t b[3];
499 b[0] = (trackXYZOut[0] - trackXYZIn[0]) / pathLength;
500 b[1] = (trackXYZOut[1] - trackXYZIn[1]) / pathLength;
501 b[2] = (trackXYZOut[2] - trackXYZIn[2]) / pathLength;
502 TGeoNode *currentnode = gGeoManager->InitTrack(trackXYZIn, b);
503 if (!currentnode) {
504 cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: start point out of geometry"<<endl;
505 return;
506 }
507
508 // loop over absorber slices and calculate absorber's parameters
509 Double_t rho = 0.; // material density (g/cm3)
510 Double_t x0 = 0.; // radiation-length (cm-1)
84f061ef 511 Double_t atomicA = 0.; // A of material
512 Double_t atomicZ = 0.; // Z of material
8cde4af5 513 Double_t localPathLength = 0;
514 Double_t remainingPathLength = pathLength;
515 Double_t zB = trackXYZIn[2];
516 Double_t zE, dzB, dzE;
517 do {
518 // Get material properties
519 TGeoMaterial *material = currentnode->GetVolume()->GetMedium()->GetMaterial();
520 rho = material->GetDensity();
521 x0 = material->GetRadLen();
522 if (!material->IsMixture()) x0 /= rho; // different normalization in the modeler for mixture
84f061ef 523 atomicA = material->GetA();
524 atomicZ = material->GetZ();
8cde4af5 525
526 // Get path length within this material
527 gGeoManager->FindNextBoundary(remainingPathLength);
528 localPathLength = gGeoManager->GetStep() + 1.e-6;
529 // Check if boundary within remaining path length. If so, make sure to cross the boundary to prepare the next step
530 if (localPathLength >= remainingPathLength) localPathLength = remainingPathLength;
531 else {
532 currentnode = gGeoManager->Step();
533 if (!currentnode) {
534 cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: navigation failed"<<endl;
535 f0 = f1 = f2 = meanRho = 0.;
536 return;
537 }
538 if (!gGeoManager->IsEntering()) {
539 // make another small step to try to enter in new absorber slice
540 gGeoManager->SetStep(0.001);
541 currentnode = gGeoManager->Step();
542 if (!gGeoManager->IsEntering() || !currentnode) {
543 cout<<"E-AliMUONTrackExtrap::GetAbsorberCorrectionParam: navigation failed"<<endl;
544 f0 = f1 = f2 = meanRho = 0.;
545 return;
546 }
547 localPathLength += 0.001;
548 }
549 }
550
551 // calculate absorber's parameters
552 zE = b[2] * localPathLength + zB;
553 dzB = zB - trackXYZIn[2];
554 dzE = zE - trackXYZIn[2];
555 f0 += localPathLength / x0;
556 f1 += (dzE*dzE - dzB*dzB) / b[2] / b[2] / x0 / 2.;
557 f2 += (dzE*dzE*dzE - dzB*dzB*dzB) / b[2] / b[2] / b[2] / x0 / 3.;
558 meanRho += localPathLength * rho;
84f061ef 559 totalELoss += BetheBloch(pTotal, localPathLength, rho, atomicA, atomicZ);
690d2205 560 sigmaELoss2 += EnergyLossFluctuation2(pTotal, localPathLength, rho, atomicA, atomicZ);
8cde4af5 561
562 // prepare next step
563 zB = zE;
564 remainingPathLength -= localPathLength;
565 } while (remainingPathLength > TGeoShape::Tolerance());
566
567 meanRho /= pathLength;
568}
569
690d2205 570//__________________________________________________________________________
ea94c18b 571Double_t AliMUONTrackExtrap::GetMCSAngle2(const AliMUONTrackParam& param, Double_t dZ, Double_t x0)
572{
573 /// Return the angular dispersion square due to multiple Coulomb scattering
574 /// through a material of thickness "dZ" and of radiation length "x0"
575 /// assuming linear propagation and using the small angle approximation.
576
577 Double_t bendingSlope = param.GetBendingSlope();
578 Double_t nonBendingSlope = param.GetNonBendingSlope();
579 Double_t inverseTotalMomentum2 = param.GetInverseBendingMomentum() * param.GetInverseBendingMomentum() *
690d2205 580 (1.0 + bendingSlope * bendingSlope) /
581 (1.0 + bendingSlope *bendingSlope + nonBendingSlope * nonBendingSlope);
ea94c18b 582 // Path length in the material
583 Double_t pathLength = TMath::Abs(dZ) * TMath::Sqrt(1.0 + bendingSlope*bendingSlope + nonBendingSlope*nonBendingSlope);
584 // relativistic velocity
585 Double_t velo = 1.;
586 // Angular dispersion square of the track (variance) in a plane perpendicular to the trajectory
587 Double_t theta02 = 0.0136 / velo * (1 + 0.038 * TMath::Log(pathLength/x0));
588
589 return theta02 * theta02 * inverseTotalMomentum2 * pathLength / x0;
590}
591
690d2205 592//__________________________________________________________________________
8cde4af5 593void AliMUONTrackExtrap::AddMCSEffect(AliMUONTrackParam *param, Double_t dZ, Double_t x0)
208f139e 594{
595 /// Add to the track parameter covariances the effects of multiple Coulomb scattering
596 /// through a material of thickness "dZ" and of radiation length "x0"
597 /// assuming linear propagation and using the small angle approximation.
598
599 Double_t bendingSlope = param->GetBendingSlope();
600 Double_t nonBendingSlope = param->GetNonBendingSlope();
690d2205 601 Double_t inverseBendingMomentum = param->GetInverseBendingMomentum();
602 Double_t inverseTotalMomentum2 = inverseBendingMomentum * inverseBendingMomentum *
603 (1.0 + bendingSlope * bendingSlope) /
604 (1.0 + bendingSlope *bendingSlope + nonBendingSlope * nonBendingSlope);
208f139e 605 // Path length in the material
606 Double_t pathLength = TMath::Abs(dZ) * TMath::Sqrt(1.0 + bendingSlope*bendingSlope + nonBendingSlope*nonBendingSlope);
607 Double_t pathLength2 = pathLength * pathLength;
608 // relativistic velocity
609 Double_t velo = 1.;
610 // Angular dispersion square of the track (variance) in a plane perpendicular to the trajectory
611 Double_t theta02 = 0.0136 / velo * (1 + 0.038 * TMath::Log(pathLength/x0));
612 theta02 *= theta02 * inverseTotalMomentum2 * pathLength / x0;
613
208f139e 614 Double_t varCoor = pathLength2 * theta02 / 3.;
615 Double_t varSlop = theta02;
616 Double_t covCorrSlope = pathLength * theta02 / 2.;
ea94c18b 617
690d2205 618 // compute derivative d(q/Pxy) / dSlopeX and d(q/Pxy) / dSlopeX
619 Double_t dqPxydSlopeX = inverseBendingMomentum * nonBendingSlope / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
620 Double_t dqPxydSlopeY = - inverseBendingMomentum * nonBendingSlope*nonBendingSlope * bendingSlope /
621 (1. + bendingSlope*bendingSlope) / (1. + nonBendingSlope*nonBendingSlope + bendingSlope*bendingSlope);
622
623 // Set MCS covariance matrix
ea94c18b 624 TMatrixD newParamCov(param->GetCovariances());
208f139e 625 // Non bending plane
ea94c18b 626 newParamCov(0,0) += varCoor; newParamCov(0,1) += covCorrSlope;
627 newParamCov(1,0) += covCorrSlope; newParamCov(1,1) += varSlop;
208f139e 628 // Bending plane
ea94c18b 629 newParamCov(2,2) += varCoor; newParamCov(2,3) += covCorrSlope;
630 newParamCov(3,2) += covCorrSlope; newParamCov(3,3) += varSlop;
690d2205 631 // Inverse bending momentum (due to dependences with bending and non bending slopes)
632 newParamCov(4,0) += dqPxydSlopeX * covCorrSlope; newParamCov(0,4) += dqPxydSlopeX * covCorrSlope;
633 newParamCov(4,1) += dqPxydSlopeX * varSlop; newParamCov(1,4) += dqPxydSlopeX * varSlop;
634 newParamCov(4,2) += dqPxydSlopeY * covCorrSlope; newParamCov(2,4) += dqPxydSlopeY * covCorrSlope;
635 newParamCov(4,3) += dqPxydSlopeY * varSlop; newParamCov(3,4) += dqPxydSlopeY * varSlop;
636 newParamCov(4,4) += (dqPxydSlopeX*dqPxydSlopeX + dqPxydSlopeY*dqPxydSlopeY) * varSlop;
208f139e 637
ea94c18b 638 // Set new covariances
639 param->SetCovariances(newParamCov);
c04e3238 640}
641
690d2205 642//__________________________________________________________________________
643void AliMUONTrackExtrap::ExtrapToVertex(AliMUONTrackParam* trackParam,
644 Double_t xVtx, Double_t yVtx, Double_t zVtx,
645 Double_t errXVtx, Double_t errYVtx,
646 Bool_t correctForMCS, Bool_t correctForEnergyLoss)
c04e3238 647{
690d2205 648 /// Main method for extrapolation to the vertex:
649 /// Returns the track parameters and covariances resulting from the extrapolation of the current trackParam
650 /// Changes parameters and covariances according to multiple scattering and energy loss corrections:
651 /// if correctForMCS=kTRUE: compute parameters using Branson correction and add correction resolution to covariances
652 /// if correctForMCS=kFALSE: add parameter dispersion due to MCS in parameter covariances
653 /// if correctForEnergyLoss=kTRUE: correct parameters for energy loss and add energy loss fluctuation to covariances
654 /// if correctForEnergyLoss=kFALSE: do nothing about energy loss
c04e3238 655
8cde4af5 656 if (trackParam->GetZ() == zVtx) return; // nothing to be done if already at vertex
c04e3238 657
8cde4af5 658 if (trackParam->GetZ() > zVtx) { // spectro. (z<0)
690d2205 659 cout<<"E-AliMUONTrackExtrap::ExtrapToVertex: Starting Z ("<<trackParam->GetZ()
660 <<") upstream the vertex (zVtx = "<<zVtx<<")"<<endl;
fac70e25 661 return;
662 }
663
8cde4af5 664 // Check the vertex position relatively to the absorber
ea94c18b 665 if (zVtx < AliMUONConstants::AbsZBeg() && zVtx > AliMUONConstants::AbsZEnd()) { // spectro. (z<0)
8cde4af5 666 cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Ending Z ("<<zVtx
690d2205 667 <<") inside the front absorber ("<<AliMUONConstants::AbsZBeg()<<","<<AliMUONConstants::AbsZEnd()<<")"<<endl;
ea94c18b 668 } else if (zVtx < AliMUONConstants::AbsZEnd() ) { // spectro. (z<0)
8cde4af5 669 cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Ending Z ("<<zVtx
690d2205 670 <<") downstream the front absorber (zAbsorberEnd = "<<AliMUONConstants::AbsZEnd()<<")"<<endl;
671 if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,zVtx);
672 else ExtrapToZ(trackParam,zVtx);
8cde4af5 673 return;
674 }
675
676 // Check the track position relatively to the absorber and extrapolate track parameters to the end of the absorber if needed
ea94c18b 677 if (trackParam->GetZ() > AliMUONConstants::AbsZBeg()) { // spectro. (z<0)
8cde4af5 678 cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Starting Z ("<<trackParam->GetZ()
690d2205 679 <<") upstream the front absorber (zAbsorberBegin = "<<AliMUONConstants::AbsZBeg()<<")"<<endl;
680 if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,zVtx);
681 else ExtrapToZ(trackParam,zVtx);
8cde4af5 682 return;
ea94c18b 683 } else if (trackParam->GetZ() > AliMUONConstants::AbsZEnd()) { // spectro. (z<0)
8cde4af5 684 cout<<"W-AliMUONTrackExtrap::ExtrapToVertex: Starting Z ("<<trackParam->GetZ()
690d2205 685 <<") inside the front absorber ("<<AliMUONConstants::AbsZBeg()<<","<<AliMUONConstants::AbsZEnd()<<")"<<endl;
c04e3238 686 } else {
690d2205 687 if (trackParam->CovariancesExist()) ExtrapToZCov(trackParam,AliMUONConstants::AbsZEnd());
688 else ExtrapToZ(trackParam,AliMUONConstants::AbsZEnd());
c04e3238 689 }
c04e3238 690
690d2205 691 // Get absorber correction parameters assuming linear propagation in absorber
8cde4af5 692 Double_t trackXYZOut[3];
693 trackXYZOut[0] = trackParam->GetNonBendingCoor();
694 trackXYZOut[1] = trackParam->GetBendingCoor();
695 trackXYZOut[2] = trackParam->GetZ();
696 Double_t trackXYZIn[3];
690d2205 697 if (correctForMCS) { // assume linear propagation until the vertex
698 trackXYZIn[2] = TMath::Min(zVtx, AliMUONConstants::AbsZBeg()); // spectro. (z<0)
699 trackXYZIn[0] = trackXYZOut[0] + (xVtx - trackXYZOut[0]) / (zVtx - trackXYZOut[2]) * (trackXYZIn[2] - trackXYZOut[2]);
700 trackXYZIn[1] = trackXYZOut[1] + (yVtx - trackXYZOut[1]) / (zVtx - trackXYZOut[2]) * (trackXYZIn[2] - trackXYZOut[2]);
701 } else {
702 AliMUONTrackParam trackParamIn(*trackParam);
703 ExtrapToZ(&trackParamIn, TMath::Min(zVtx, AliMUONConstants::AbsZBeg()));
704 trackXYZIn[0] = trackParamIn.GetNonBendingCoor();
705 trackXYZIn[1] = trackParamIn.GetBendingCoor();
706 trackXYZIn[2] = trackParamIn.GetZ();
707 }
84f061ef 708 Double_t pTot = trackParam->P();
8cde4af5 709 Double_t pathLength = 0.;
710 Double_t f0 = 0.;
711 Double_t f1 = 0.;
712 Double_t f2 = 0.;
713 Double_t meanRho = 0.;
84f061ef 714 Double_t deltaP = 0.;
690d2205 715 Double_t sigmaDeltaP2 = 0.;
716 GetAbsorberCorrectionParam(trackXYZIn,trackXYZOut,pTot,pathLength,f0,f1,f2,meanRho,deltaP,sigmaDeltaP2);
8cde4af5 717
690d2205 718 // Compute track parameters and covariances at vertex according to correctForMCS and correctForEnergyLoss flags
719 if (correctForMCS) {
fac70e25 720
690d2205 721 if (correctForEnergyLoss) {
722
723 // Correct for multiple scattering and energy loss
724 CorrectELossEffectInAbsorber(trackParam, 0.5*deltaP, 0.5*sigmaDeltaP2);
725 CorrectMCSEffectInAbsorber(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx,
726 trackXYZIn[2], pathLength, f0, f1, f2);
727 CorrectELossEffectInAbsorber(trackParam, 0.5*deltaP, 0.5*sigmaDeltaP2);
728
729 } else {
730
731 // Correct for multiple scattering
732 CorrectMCSEffectInAbsorber(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx,
733 trackXYZIn[2], pathLength, f0, f1, f2);
734 }
fac70e25 735
fac70e25 736 } else {
690d2205 737
738 if (correctForEnergyLoss) {
739
740 // Correct for energy loss
741 CorrectELossEffectInAbsorber(trackParam, 0.5*deltaP, 0.5*sigmaDeltaP2);
742 AddMCSEffectInAbsorber(trackParam, pathLength, f0, f1, f2);
743 ExtrapToZCov(trackParam, trackXYZIn[2]);
744 CorrectELossEffectInAbsorber(trackParam, 0.5*deltaP, 0.5*sigmaDeltaP2);
745 ExtrapToZCov(trackParam, zVtx);
746
747 } else {
748
749 // Correct for multiple scattering and energy loss
750 AddMCSEffectInAbsorber(trackParam, pathLength, f0, f1, f2);
751 ExtrapToZCov(trackParam, zVtx);
752
753 }
754
fac70e25 755 }
8cde4af5 756
fac70e25 757}
758
690d2205 759//__________________________________________________________________________
760void AliMUONTrackExtrap::ExtrapToVertex(AliMUONTrackParam* trackParam,
761 Double_t xVtx, Double_t yVtx, Double_t zVtx,
762 Double_t errXVtx, Double_t errYVtx)
763{
764 /// Extrapolate track parameters to vertex, corrected for multiple scattering and energy loss effects
765 /// Add branson correction resolution and energy loss fluctuation to parameter covariances
766 ExtrapToVertex(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx, kTRUE, kTRUE);
767}
768
769//__________________________________________________________________________
770void AliMUONTrackExtrap::ExtrapToVertexWithoutELoss(AliMUONTrackParam* trackParam,
771 Double_t xVtx, Double_t yVtx, Double_t zVtx,
772 Double_t errXVtx, Double_t errYVtx)
773{
774 /// Extrapolate track parameters to vertex, corrected for multiple scattering effects only
775 /// Add branson correction resolution to parameter covariances
776 ExtrapToVertex(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx, kTRUE, kFALSE);
777}
778
779//__________________________________________________________________________
780void AliMUONTrackExtrap::ExtrapToVertexWithoutBranson(AliMUONTrackParam* trackParam, Double_t zVtx)
781{
782 /// Extrapolate track parameters to vertex, corrected for energy loss effects only
783 /// Add dispersion due to multiple scattering and energy loss fluctuation to parameter covariances
784 ExtrapToVertex(trackParam, 0., 0., zVtx, 0., 0., kFALSE, kTRUE);
785}
786
787//__________________________________________________________________________
788void AliMUONTrackExtrap::ExtrapToVertexUncorrected(AliMUONTrackParam* trackParam, Double_t zVtx)
789{
790 /// Extrapolate track parameters to vertex without multiple scattering and energy loss corrections
791 /// Add dispersion due to multiple scattering to parameter covariances
792 ExtrapToVertex(trackParam, 0., 0., zVtx, 0., 0., kFALSE, kFALSE);
793}
794
795//__________________________________________________________________________
fac70e25 796Double_t AliMUONTrackExtrap::TotalMomentumEnergyLoss(AliMUONTrackParam* trackParam, Double_t xVtx, Double_t yVtx, Double_t zVtx)
797{
798 /// Calculate the total momentum energy loss in-between the track position and the vertex assuming a linear propagation
799
800 if (trackParam->GetZ() == zVtx) return 0.; // nothing to be done if already at vertex
8cde4af5 801
fac70e25 802 // Check whether the geometry is available
803 if (!gGeoManager) {
804 cout<<"E-AliMUONTrackExtrap::TotalMomentumEnergyLoss: no TGeo"<<endl;
805 return 0.;
806 }
807
808 // Get encountered material correction parameters assuming linear propagation from vertex to the track position
809 Double_t trackXYZOut[3];
810 trackXYZOut[0] = trackParam->GetNonBendingCoor();
811 trackXYZOut[1] = trackParam->GetBendingCoor();
812 trackXYZOut[2] = trackParam->GetZ();
813 Double_t trackXYZIn[3];
814 trackXYZIn[0] = xVtx;
815 trackXYZIn[1] = yVtx;
816 trackXYZIn[2] = zVtx;
84f061ef 817 Double_t pTot = trackParam->P();
fac70e25 818 Double_t pathLength = 0.;
819 Double_t f0 = 0.;
820 Double_t f1 = 0.;
821 Double_t f2 = 0.;
822 Double_t meanRho = 0.;
84f061ef 823 Double_t totalELoss = 0.;
690d2205 824 Double_t sigmaELoss2 = 0.;
825 GetAbsorberCorrectionParam(trackXYZIn,trackXYZOut,pTot,pathLength,f0,f1,f2,meanRho,totalELoss,sigmaELoss2);
fac70e25 826
84f061ef 827 return totalELoss;
c04e3238 828}
829
690d2205 830//__________________________________________________________________________
84f061ef 831Double_t AliMUONTrackExtrap::BetheBloch(Double_t pTotal, Double_t pathLength, Double_t rho, Double_t atomicA, Double_t atomicZ)
c04e3238 832{
84f061ef 833 /// Returns the mean total momentum energy loss of muon with total momentum='pTotal'
834 /// in the absorber layer of lenght='pathLength', density='rho', A='atomicA' and Z='atomicZ'
835 Double_t muMass = 0.105658369; // GeV
836 Double_t eMass = 0.510998918e-3; // GeV
837 Double_t k = 0.307075e-3; // GeV.g^-1.cm^2
838 Double_t i = 9.5e-9; // mean exitation energy per atomic Z (GeV)
8cde4af5 839 Double_t p2=pTotal*pTotal;
840 Double_t beta2=p2/(p2 + muMass*muMass);
8cde4af5 841
84f061ef 842 Double_t w = k * rho * pathLength * atomicZ / atomicA / beta2;
843
8cde4af5 844 if (beta2/(1-beta2)>3.5*3.5)
690d2205 845 return w * (log(2.*eMass*3.5/(i*atomicZ)) + 0.5*log(beta2/(1-beta2)) - beta2);
846
84f061ef 847 return w * (log(2.*eMass*beta2/(1-beta2)/(i*atomicZ)) - beta2);
c04e3238 848}
849
690d2205 850//__________________________________________________________________________
851Double_t AliMUONTrackExtrap::EnergyLossFluctuation2(Double_t pTotal, Double_t pathLength, Double_t rho, Double_t atomicA, Double_t atomicZ)
852{
853 /// Returns the total momentum energy loss fluctuation of muon with total momentum='pTotal'
854 /// in the absorber layer of lenght='pathLength', density='rho', A='atomicA' and Z='atomicZ'
855 Double_t muMass = 0.105658369; // GeV
856 //Double_t eMass = 0.510998918e-3; // GeV
857 Double_t k = 0.307075e-3; // GeV.g^-1.cm^2
858 Double_t p2=pTotal*pTotal;
859 Double_t beta2=p2/(p2 + muMass*muMass);
860
861 Double_t fwhm = 2. * k * rho * pathLength * atomicZ / atomicA / beta2; // FWHM of the energy loss Landau distribution
862 Double_t sigma2 = fwhm * fwhm / (8.*log(2.)); // gaussian: fwmh = 2 * srqt(2*ln(2)) * sigma (i.e. fwmh = 2.35 * sigma)
863
864 //sigma2 = k * rho * pathLength * atomicZ / atomicA * eMass; // sigma2 of the energy loss gaussian distribution
865
866 return sigma2;
867}
868
869//__________________________________________________________________________
870void AliMUONTrackExtrap::Cov2CovP(const TMatrixD &param, TMatrixD &cov)
871{
872 /// change coordinate system: (X, SlopeX, Y, SlopeY, q/Pyz) -> (X, SlopeX, Y, SlopeY, q*PTot)
873 /// parameters (param) are given in the (X, SlopeX, Y, SlopeY, q/Pyz) coordinate system
874
875 // charge * total momentum
876 Double_t qPTot = TMath::Sqrt(1. + param(1,0)*param(1,0) + param(3,0)*param(3,0)) /
877 TMath::Sqrt(1. + param(3,0)*param(3,0)) / param(4,0);
878
879 // Jacobian of the opposite transformation
880 TMatrixD jacob(5,5);
881 jacob.UnitMatrix();
882 jacob(4,1) = qPTot * param(1,0) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
883 jacob(4,3) = - qPTot * param(1,0) * param(1,0) * param(3,0) /
884 (1. + param(3,0)*param(3,0)) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
885 jacob(4,4) = - qPTot / param(4,0);
886
887 // compute covariances in new coordinate system
888 TMatrixD tmp(cov,TMatrixD::kMultTranspose,jacob);
889 cov.Mult(jacob,tmp);
890}
891
892//__________________________________________________________________________
893void AliMUONTrackExtrap::CovP2Cov(const TMatrixD &param, TMatrixD &covP)
894{
895 /// change coordinate system: (X, SlopeX, Y, SlopeY, q*PTot) -> (X, SlopeX, Y, SlopeY, q/Pyz)
896 /// parameters (param) are given in the (X, SlopeX, Y, SlopeY, q/Pyz) coordinate system
897
898 // charge * total momentum
899 Double_t qPTot = TMath::Sqrt(1. + param(1,0)*param(1,0) + param(3,0)*param(3,0)) /
900 TMath::Sqrt(1. + param(3,0)*param(3,0)) / param(4,0);
901
902 // Jacobian of the transformation
903 TMatrixD jacob(5,5);
904 jacob.UnitMatrix();
905 jacob(4,1) = param(4,0) * param(1,0) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
906 jacob(4,3) = - param(4,0) * param(1,0) * param(1,0) * param(3,0) /
907 (1. + param(3,0)*param(3,0)) / (1. + param(1,0)*param(1,0) + param(3,0)*param(3,0));
908 jacob(4,4) = - param(4,0) / qPTot;
909
910 // compute covariances in new coordinate system
911 TMatrixD tmp(covP,TMatrixD::kMultTranspose,jacob);
912 covP.Mult(jacob,tmp);
913}
914
c04e3238 915 //__________________________________________________________________________
916void AliMUONTrackExtrap::ExtrapOneStepHelix(Double_t charge, Double_t step, Double_t *vect, Double_t *vout)
917{
71a2d3aa 918/// <pre>
c04e3238 919/// ******************************************************************
920/// * *
921/// * Performs the tracking of one step in a magnetic field *
922/// * The trajectory is assumed to be a helix in a constant field *
923/// * taken at the mid point of the step. *
924/// * Parameters: *
925/// * input *
926/// * STEP =arc length of the step asked *
927/// * VECT =input vector (position,direction cos and momentum) *
928/// * CHARGE= electric charge of the particle *
929/// * output *
930/// * VOUT = same as VECT after completion of the step *
931/// * *
2060b217 932/// * ==>Called by : USER, GUSWIM *
c04e3238 933/// * Author m.hansroul ********* *
934/// * modified s.egli, s.v.levonian *
935/// * modified v.perevoztchikov
936/// * *
937/// ******************************************************************
71a2d3aa 938/// </pre>
c04e3238 939
940// modif: everything in double precision
941
942 Double_t xyz[3], h[4], hxp[3];
943 Double_t h2xy, hp, rho, tet;
944 Double_t sint, sintt, tsint, cos1t;
945 Double_t f1, f2, f3, f4, f5, f6;
946
947 const Int_t kix = 0;
948 const Int_t kiy = 1;
949 const Int_t kiz = 2;
950 const Int_t kipx = 3;
951 const Int_t kipy = 4;
952 const Int_t kipz = 5;
953 const Int_t kipp = 6;
954
955 const Double_t kec = 2.9979251e-4;
956 //
957 // ------------------------------------------------------------------
958 //
959 // units are kgauss,centimeters,gev/c
960 //
961 vout[kipp] = vect[kipp];
962 if (TMath::Abs(charge) < 0.00001) {
963 for (Int_t i = 0; i < 3; i++) {
964 vout[i] = vect[i] + step * vect[i+3];
965 vout[i+3] = vect[i+3];
966 }
967 return;
968 }
969 xyz[0] = vect[kix] + 0.5 * step * vect[kipx];
970 xyz[1] = vect[kiy] + 0.5 * step * vect[kipy];
971 xyz[2] = vect[kiz] + 0.5 * step * vect[kipz];
972
973 //cmodif: call gufld (xyz, h) changed into:
974 GetField (xyz, h);
975
976 h2xy = h[0]*h[0] + h[1]*h[1];
977 h[3] = h[2]*h[2]+ h2xy;
978 if (h[3] < 1.e-12) {
979 for (Int_t i = 0; i < 3; i++) {
980 vout[i] = vect[i] + step * vect[i+3];
981 vout[i+3] = vect[i+3];
982 }
983 return;
984 }
985 if (h2xy < 1.e-12*h[3]) {
986 ExtrapOneStepHelix3(charge*h[2], step, vect, vout);
987 return;
988 }
989 h[3] = TMath::Sqrt(h[3]);
990 h[0] /= h[3];
991 h[1] /= h[3];
992 h[2] /= h[3];
993 h[3] *= kec;
994
995 hxp[0] = h[1]*vect[kipz] - h[2]*vect[kipy];
996 hxp[1] = h[2]*vect[kipx] - h[0]*vect[kipz];
997 hxp[2] = h[0]*vect[kipy] - h[1]*vect[kipx];
998
999 hp = h[0]*vect[kipx] + h[1]*vect[kipy] + h[2]*vect[kipz];
1000
1001 rho = -charge*h[3]/vect[kipp];
1002 tet = rho * step;
1003
1004 if (TMath::Abs(tet) > 0.15) {
1005 sint = TMath::Sin(tet);
1006 sintt = (sint/tet);
1007 tsint = (tet-sint)/tet;
1008 cos1t = 2.*(TMath::Sin(0.5*tet))*(TMath::Sin(0.5*tet))/tet;
1009 } else {
1010 tsint = tet*tet/36.;
1011 sintt = (1. - tsint);
1012 sint = tet*sintt;
1013 cos1t = 0.5*tet;
1014 }
1015
1016 f1 = step * sintt;
1017 f2 = step * cos1t;
1018 f3 = step * tsint * hp;
1019 f4 = -tet*cos1t;
1020 f5 = sint;
1021 f6 = tet * cos1t * hp;
1022
1023 vout[kix] = vect[kix] + f1*vect[kipx] + f2*hxp[0] + f3*h[0];
1024 vout[kiy] = vect[kiy] + f1*vect[kipy] + f2*hxp[1] + f3*h[1];
1025 vout[kiz] = vect[kiz] + f1*vect[kipz] + f2*hxp[2] + f3*h[2];
1026
1027 vout[kipx] = vect[kipx] + f4*vect[kipx] + f5*hxp[0] + f6*h[0];
1028 vout[kipy] = vect[kipy] + f4*vect[kipy] + f5*hxp[1] + f6*h[1];
1029 vout[kipz] = vect[kipz] + f4*vect[kipz] + f5*hxp[2] + f6*h[2];
1030
1031 return;
1032}
1033
1034 //__________________________________________________________________________
1035void AliMUONTrackExtrap::ExtrapOneStepHelix3(Double_t field, Double_t step, Double_t *vect, Double_t *vout)
1036{
71a2d3aa 1037/// <pre>
c04e3238 1038/// ******************************************************************
1039/// * *
1040/// * Tracking routine in a constant field oriented *
1041/// * along axis 3 *
1042/// * Tracking is performed with a conventional *
1043/// * helix step method *
1044/// * *
2060b217 1045/// * ==>Called by : USER, GUSWIM *
c04e3238 1046/// * Authors R.Brun, M.Hansroul ********* *
1047/// * Rewritten V.Perevoztchikov
1048/// * *
1049/// ******************************************************************
71a2d3aa 1050/// </pre>
c04e3238 1051
1052 Double_t hxp[3];
1053 Double_t h4, hp, rho, tet;
1054 Double_t sint, sintt, tsint, cos1t;
1055 Double_t f1, f2, f3, f4, f5, f6;
1056
1057 const Int_t kix = 0;
1058 const Int_t kiy = 1;
1059 const Int_t kiz = 2;
1060 const Int_t kipx = 3;
1061 const Int_t kipy = 4;
1062 const Int_t kipz = 5;
1063 const Int_t kipp = 6;
1064
1065 const Double_t kec = 2.9979251e-4;
1066
1067//
1068// ------------------------------------------------------------------
1069//
1070// units are kgauss,centimeters,gev/c
1071//
1072 vout[kipp] = vect[kipp];
1073 h4 = field * kec;
1074
1075 hxp[0] = - vect[kipy];
1076 hxp[1] = + vect[kipx];
1077
1078 hp = vect[kipz];
1079
1080 rho = -h4/vect[kipp];
1081 tet = rho * step;
1082 if (TMath::Abs(tet) > 0.15) {
1083 sint = TMath::Sin(tet);
1084 sintt = (sint/tet);
1085 tsint = (tet-sint)/tet;
1086 cos1t = 2.* TMath::Sin(0.5*tet) * TMath::Sin(0.5*tet)/tet;
1087 } else {
1088 tsint = tet*tet/36.;
1089 sintt = (1. - tsint);
1090 sint = tet*sintt;
1091 cos1t = 0.5*tet;
1092 }
1093
1094 f1 = step * sintt;
1095 f2 = step * cos1t;
1096 f3 = step * tsint * hp;
1097 f4 = -tet*cos1t;
1098 f5 = sint;
1099 f6 = tet * cos1t * hp;
1100
1101 vout[kix] = vect[kix] + f1*vect[kipx] + f2*hxp[0];
1102 vout[kiy] = vect[kiy] + f1*vect[kipy] + f2*hxp[1];
1103 vout[kiz] = vect[kiz] + f1*vect[kipz] + f3;
1104
1105 vout[kipx] = vect[kipx] + f4*vect[kipx] + f5*hxp[0];
1106 vout[kipy] = vect[kipy] + f4*vect[kipy] + f5*hxp[1];
1107 vout[kipz] = vect[kipz] + f4*vect[kipz] + f6;
1108
1109 return;
1110}
8cde4af5 1111
c04e3238 1112 //__________________________________________________________________________
1113void AliMUONTrackExtrap::ExtrapOneStepRungekutta(Double_t charge, Double_t step, Double_t* vect, Double_t* vout)
1114{
71a2d3aa 1115/// <pre>
c04e3238 1116/// ******************************************************************
1117/// * *
1118/// * Runge-Kutta method for tracking a particle through a magnetic *
1119/// * field. Uses Nystroem algorithm (See Handbook Nat. Bur. of *
1120/// * Standards, procedure 25.5.20) *
1121/// * *
1122/// * Input parameters *
1123/// * CHARGE Particle charge *
1124/// * STEP Step size *
1125/// * VECT Initial co-ords,direction cosines,momentum *
1126/// * Output parameters *
1127/// * VOUT Output co-ords,direction cosines,momentum *
1128/// * User routine called *
1129/// * CALL GUFLD(X,F) *
1130/// * *
2060b217 1131/// * ==>Called by : USER, GUSWIM *
c04e3238 1132/// * Authors R.Brun, M.Hansroul ********* *
1133/// * V.Perevoztchikov (CUT STEP implementation) *
1134/// * *
1135/// * *
1136/// ******************************************************************
71a2d3aa 1137/// </pre>
c04e3238 1138
1139 Double_t h2, h4, f[4];
1140 Double_t xyzt[3], a, b, c, ph,ph2;
1141 Double_t secxs[4],secys[4],seczs[4],hxp[3];
1142 Double_t g1, g2, g3, g4, g5, g6, ang2, dxt, dyt, dzt;
1143 Double_t est, at, bt, ct, cba;
1144 Double_t f1, f2, f3, f4, rho, tet, hnorm, hp, rho1, sint, cost;
1145
1146 Double_t x;
1147 Double_t y;
1148 Double_t z;
1149
1150 Double_t xt;
1151 Double_t yt;
1152 Double_t zt;
1153
1154 Double_t maxit = 1992;
1155 Double_t maxcut = 11;
1156
1157 const Double_t kdlt = 1e-4;
1158 const Double_t kdlt32 = kdlt/32.;
1159 const Double_t kthird = 1./3.;
1160 const Double_t khalf = 0.5;
1161 const Double_t kec = 2.9979251e-4;
1162
1163 const Double_t kpisqua = 9.86960440109;
1164 const Int_t kix = 0;
1165 const Int_t kiy = 1;
1166 const Int_t kiz = 2;
1167 const Int_t kipx = 3;
1168 const Int_t kipy = 4;
1169 const Int_t kipz = 5;
1170
1171 // *.
1172 // *. ------------------------------------------------------------------
1173 // *.
1174 // * this constant is for units cm,gev/c and kgauss
1175 // *
1176 Int_t iter = 0;
1177 Int_t ncut = 0;
1178 for(Int_t j = 0; j < 7; j++)
1179 vout[j] = vect[j];
1180
1181 Double_t pinv = kec * charge / vect[6];
1182 Double_t tl = 0.;
1183 Double_t h = step;
1184 Double_t rest;
1185
1186
1187 do {
1188 rest = step - tl;
1189 if (TMath::Abs(h) > TMath::Abs(rest)) h = rest;
1190 //cmodif: call gufld(vout,f) changed into:
1191
1192 GetField(vout,f);
1193
1194 // *
1195 // * start of integration
1196 // *
1197 x = vout[0];
1198 y = vout[1];
1199 z = vout[2];
1200 a = vout[3];
1201 b = vout[4];
1202 c = vout[5];
1203
1204 h2 = khalf * h;
1205 h4 = khalf * h2;
1206 ph = pinv * h;
1207 ph2 = khalf * ph;
1208 secxs[0] = (b * f[2] - c * f[1]) * ph2;
1209 secys[0] = (c * f[0] - a * f[2]) * ph2;
1210 seczs[0] = (a * f[1] - b * f[0]) * ph2;
1211 ang2 = (secxs[0]*secxs[0] + secys[0]*secys[0] + seczs[0]*seczs[0]);
1212 if (ang2 > kpisqua) break;
1213
1214 dxt = h2 * a + h4 * secxs[0];
1215 dyt = h2 * b + h4 * secys[0];
1216 dzt = h2 * c + h4 * seczs[0];
1217 xt = x + dxt;
1218 yt = y + dyt;
1219 zt = z + dzt;
1220 // *
1221 // * second intermediate point
1222 // *
1223
1224 est = TMath::Abs(dxt) + TMath::Abs(dyt) + TMath::Abs(dzt);
1225 if (est > h) {
1226 if (ncut++ > maxcut) break;
1227 h *= khalf;
1228 continue;
1229 }
1230
1231 xyzt[0] = xt;
1232 xyzt[1] = yt;
1233 xyzt[2] = zt;
1234
1235 //cmodif: call gufld(xyzt,f) changed into:
1236 GetField(xyzt,f);
1237
1238 at = a + secxs[0];
1239 bt = b + secys[0];
1240 ct = c + seczs[0];
1241
1242 secxs[1] = (bt * f[2] - ct * f[1]) * ph2;
1243 secys[1] = (ct * f[0] - at * f[2]) * ph2;
1244 seczs[1] = (at * f[1] - bt * f[0]) * ph2;
1245 at = a + secxs[1];
1246 bt = b + secys[1];
1247 ct = c + seczs[1];
1248 secxs[2] = (bt * f[2] - ct * f[1]) * ph2;
1249 secys[2] = (ct * f[0] - at * f[2]) * ph2;
1250 seczs[2] = (at * f[1] - bt * f[0]) * ph2;
1251 dxt = h * (a + secxs[2]);
1252 dyt = h * (b + secys[2]);
1253 dzt = h * (c + seczs[2]);
1254 xt = x + dxt;
1255 yt = y + dyt;
1256 zt = z + dzt;
1257 at = a + 2.*secxs[2];
1258 bt = b + 2.*secys[2];
1259 ct = c + 2.*seczs[2];
1260
1261 est = TMath::Abs(dxt)+TMath::Abs(dyt)+TMath::Abs(dzt);
1262 if (est > 2.*TMath::Abs(h)) {
1263 if (ncut++ > maxcut) break;
1264 h *= khalf;
1265 continue;
1266 }
1267
1268 xyzt[0] = xt;
1269 xyzt[1] = yt;
1270 xyzt[2] = zt;
1271
1272 //cmodif: call gufld(xyzt,f) changed into:
1273 GetField(xyzt,f);
1274
1275 z = z + (c + (seczs[0] + seczs[1] + seczs[2]) * kthird) * h;
1276 y = y + (b + (secys[0] + secys[1] + secys[2]) * kthird) * h;
1277 x = x + (a + (secxs[0] + secxs[1] + secxs[2]) * kthird) * h;
1278
1279 secxs[3] = (bt*f[2] - ct*f[1])* ph2;
1280 secys[3] = (ct*f[0] - at*f[2])* ph2;
1281 seczs[3] = (at*f[1] - bt*f[0])* ph2;
1282 a = a+(secxs[0]+secxs[3]+2. * (secxs[1]+secxs[2])) * kthird;
1283 b = b+(secys[0]+secys[3]+2. * (secys[1]+secys[2])) * kthird;
1284 c = c+(seczs[0]+seczs[3]+2. * (seczs[1]+seczs[2])) * kthird;
1285
1286 est = TMath::Abs(secxs[0]+secxs[3] - (secxs[1]+secxs[2]))
1287 + TMath::Abs(secys[0]+secys[3] - (secys[1]+secys[2]))
1288 + TMath::Abs(seczs[0]+seczs[3] - (seczs[1]+seczs[2]));
1289
1290 if (est > kdlt && TMath::Abs(h) > 1.e-4) {
1291 if (ncut++ > maxcut) break;
1292 h *= khalf;
1293 continue;
1294 }
1295
1296 ncut = 0;
1297 // * if too many iterations, go to helix
1298 if (iter++ > maxit) break;
1299
1300 tl += h;
1301 if (est < kdlt32)
1302 h *= 2.;
1303 cba = 1./ TMath::Sqrt(a*a + b*b + c*c);
1304 vout[0] = x;
1305 vout[1] = y;
1306 vout[2] = z;
1307 vout[3] = cba*a;
1308 vout[4] = cba*b;
1309 vout[5] = cba*c;
1310 rest = step - tl;
1311 if (step < 0.) rest = -rest;
1312 if (rest < 1.e-5*TMath::Abs(step)) return;
1313
1314 } while(1);
1315
1316 // angle too big, use helix
1317
1318 f1 = f[0];
1319 f2 = f[1];
1320 f3 = f[2];
1321 f4 = TMath::Sqrt(f1*f1+f2*f2+f3*f3);
1322 rho = -f4*pinv;
1323 tet = rho * step;
1324
1325 hnorm = 1./f4;
1326 f1 = f1*hnorm;
1327 f2 = f2*hnorm;
1328 f3 = f3*hnorm;
1329
1330 hxp[0] = f2*vect[kipz] - f3*vect[kipy];
1331 hxp[1] = f3*vect[kipx] - f1*vect[kipz];
1332 hxp[2] = f1*vect[kipy] - f2*vect[kipx];
1333
1334 hp = f1*vect[kipx] + f2*vect[kipy] + f3*vect[kipz];
1335
1336 rho1 = 1./rho;
1337 sint = TMath::Sin(tet);
1338 cost = 2.*TMath::Sin(khalf*tet)*TMath::Sin(khalf*tet);
1339
1340 g1 = sint*rho1;
1341 g2 = cost*rho1;
1342 g3 = (tet-sint) * hp*rho1;
1343 g4 = -cost;
1344 g5 = sint;
1345 g6 = cost * hp;
1346
1347 vout[kix] = vect[kix] + g1*vect[kipx] + g2*hxp[0] + g3*f1;
1348 vout[kiy] = vect[kiy] + g1*vect[kipy] + g2*hxp[1] + g3*f2;
1349 vout[kiz] = vect[kiz] + g1*vect[kipz] + g2*hxp[2] + g3*f3;
1350
1351 vout[kipx] = vect[kipx] + g4*vect[kipx] + g5*hxp[0] + g6*f1;
1352 vout[kipy] = vect[kipy] + g4*vect[kipy] + g5*hxp[1] + g6*f2;
1353 vout[kipz] = vect[kipz] + g4*vect[kipz] + g5*hxp[2] + g6*f3;
1354
1355 return;
1356}
8cde4af5 1357
c04e3238 1358//___________________________________________________________
690d2205 1359void AliMUONTrackExtrap::GetField(Double_t *Position, Double_t *Field)
c04e3238 1360{
1361 /// interface for arguments in double precision (Why ? ChF)
1362 Float_t x[3], b[3];
690d2205 1363
c04e3238 1364 x[0] = Position[0]; x[1] = Position[1]; x[2] = Position[2];
690d2205 1365
c04e3238 1366 if (fgkField) fgkField->Field(x,b);
1367 else {
1368 cout<<"F-AliMUONTrackExtrap::GetField: fgkField = 0x0"<<endl;
1369 exit(-1);
1370 }
1371
1372 Field[0] = b[0]; Field[1] = b[1]; Field[2] = b[2];
690d2205 1373
c04e3238 1374 return;
1375}