- Welding section on absorber side (LHCVC2C_001)
[u/mrichter/AliRoot.git] / MUON / AliMUONTrackParam.cxx
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a9e2aefa 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
88cb7938 16/* $Id$ */
a9e2aefa 17
3831f268 18///////////////////////////////////////////////////
19//
20// Track parameters
21// in
22// ALICE
23// dimuon
24// spectrometer
a9e2aefa 25//
3831f268 26///////////////////////////////////////////////////
a9e2aefa 27
70479d0e 28#include <Riostream.h>
a9e2aefa 29
30#include "AliCallf77.h"
3831f268 31#include "AliMUON.h"
a9e2aefa 32#include "AliMUONTrackParam.h"
3831f268 33#include "AliMUONChamber.h"
a9e2aefa 34#include "AliRun.h"
94de3818 35#include "AliMagF.h"
a9e2aefa 36
37ClassImp(AliMUONTrackParam) // Class implementation in ROOT context
38
a6f03ddb 39 // A few calls in Fortran or from Fortran (extrap.F).
40 // Needed, instead of calls to Geant subroutines,
41 // because double precision is necessary for track fit converging with Minuit.
42 // The "extrap" functions should be translated into C++ ????
a9e2aefa 43#ifndef WIN32
a6f03ddb 44# define extrap_onestep_helix extrap_onestep_helix_
45# define extrap_onestep_helix3 extrap_onestep_helix3_
46# define extrap_onestep_rungekutta extrap_onestep_rungekutta_
47# define gufld_double gufld_double_
a9e2aefa 48#else
a6f03ddb 49# define extrap_onestep_helix EXTRAP_ONESTEP_HELIX
50# define extrap_onestep_helix3 EXTRAP_ONESTEP_HELIX3
51# define extrap_onestep_rungekutta EXTRAP_ONESTEP_RUNGEKUTTA
52# define gufld_double GUFLD_DOUBLE
a9e2aefa 53#endif
54
a6f03ddb 55extern "C" {
56 void type_of_call extrap_onestep_helix
57 (Double_t &Charge, Double_t &StepLength, Double_t *VGeant3, Double_t *VGeant3New);
58
59 void type_of_call extrap_onestep_helix3
60 (Double_t &Field, Double_t &StepLength, Double_t *VGeant3, Double_t *VGeant3New);
61
62 void type_of_call extrap_onestep_rungekutta
63 (Double_t &Charge, Double_t &StepLength, Double_t *VGeant3, Double_t *VGeant3New);
64
65 void type_of_call gufld_double(Double_t *Position, Double_t *Field) {
66 // interface to "gAlice->Field()->Field" for arguments in double precision
67 Float_t x[3], b[3];
68 x[0] = Position[0]; x[1] = Position[1]; x[2] = Position[2];
69 gAlice->Field()->Field(x, b);
70 Field[0] = b[0]; Field[1] = b[1]; Field[2] = b[2];
71 }
a9e2aefa 72}
61adb9bd 73 //_________________________________________________________________________
74
75AliMUONTrackParam& AliMUONTrackParam::operator=(const AliMUONTrackParam& MUONTrackParam)
76{
77 if (this == &MUONTrackParam)
78 return *this;
79
80 fInverseBendingMomentum = MUONTrackParam.fInverseBendingMomentum;
81 fBendingSlope = MUONTrackParam.fBendingSlope;
82 fNonBendingSlope = MUONTrackParam.fNonBendingSlope;
83 fZ = MUONTrackParam.fZ;
84 fBendingCoor = MUONTrackParam.fBendingCoor;
85 fNonBendingCoor = MUONTrackParam.fNonBendingCoor;
86
87 return *this;
88}
89 //_________________________________________________________________________
90AliMUONTrackParam::AliMUONTrackParam(const AliMUONTrackParam& MUONTrackParam):TObject(MUONTrackParam)
91{
92 fInverseBendingMomentum = MUONTrackParam.fInverseBendingMomentum;
93 fBendingSlope = MUONTrackParam.fBendingSlope;
94 fNonBendingSlope = MUONTrackParam.fNonBendingSlope;
95 fZ = MUONTrackParam.fZ;
96 fBendingCoor = MUONTrackParam.fBendingCoor;
97 fNonBendingCoor = MUONTrackParam.fNonBendingCoor;
98}
a9e2aefa 99
a9e2aefa 100 //__________________________________________________________________________
101void AliMUONTrackParam::ExtrapToZ(Double_t Z)
102{
103 // Track parameter extrapolation to the plane at "Z".
104 // On return, the track parameters resulting from the extrapolation
105 // replace the current track parameters.
a9e2aefa 106 if (this->fZ == Z) return; // nothing to be done if same Z
107 Double_t forwardBackward; // +1 if forward, -1 if backward
5b64e914 108 if (Z < this->fZ) forwardBackward = 1.0; // spectro. z<0
a9e2aefa 109 else forwardBackward = -1.0;
a6f03ddb 110 Double_t vGeant3[7], vGeant3New[7]; // 7 in parameter ????
a9e2aefa 111 Int_t iGeant3, stepNumber;
112 Int_t maxStepNumber = 5000; // in parameter ????
113 // For safety: return kTRUE or kFALSE ????
a6f03ddb 114 // Parameter vector for calling EXTRAP_ONESTEP
a9e2aefa 115 SetGeant3Parameters(vGeant3, forwardBackward);
956019b6 116 // sign of charge (sign of fInverseBendingMomentum if forward motion)
a6f03ddb 117 // must be changed if backward extrapolation
956019b6 118 Double_t chargeExtrap = forwardBackward *
119 TMath::Sign(Double_t(1.0), this->fInverseBendingMomentum);
a9e2aefa 120 Double_t stepLength = 6.0; // in parameter ????
121 // Extrapolation loop
122 stepNumber = 0;
5b64e914 123 while (((-forwardBackward * (vGeant3[2] - Z)) <= 0.0) && // spectro. z<0
a9e2aefa 124 (stepNumber < maxStepNumber)) {
125 stepNumber++;
a6f03ddb 126 // Option for switching between helix and Runge-Kutta ????
127 // extrap_onestep_rungekutta(chargeExtrap, stepLength, vGeant3, vGeant3New);
128 extrap_onestep_helix(chargeExtrap, stepLength, vGeant3, vGeant3New);
5b64e914 129 if ((-forwardBackward * (vGeant3New[2] - Z)) > 0.0) break; // one is beyond Z spectro. z<0
a9e2aefa 130 // better use TArray ????
131 for (iGeant3 = 0; iGeant3 < 7; iGeant3++)
132 {vGeant3[iGeant3] = vGeant3New[iGeant3];}
133 }
134 // check maxStepNumber ????
a9e2aefa 135 // Interpolation back to exact Z (2nd order)
136 // should be in function ???? using TArray ????
137 Double_t dZ12 = vGeant3New[2] - vGeant3[2]; // 1->2
138 Double_t dZ1i = Z - vGeant3[2]; // 1-i
139 Double_t dZi2 = vGeant3New[2] - Z; // i->2
140 Double_t xPrime = (vGeant3New[0] - vGeant3[0]) / dZ12;
141 Double_t xSecond =
142 ((vGeant3New[3] / vGeant3New[5]) - (vGeant3[3] / vGeant3[5])) / dZ12;
143 Double_t yPrime = (vGeant3New[1] - vGeant3[1]) / dZ12;
144 Double_t ySecond =
145 ((vGeant3New[4] / vGeant3New[5]) - (vGeant3[4] / vGeant3[5])) / dZ12;
146 vGeant3[0] = vGeant3[0] + xPrime * dZ1i - 0.5 * xSecond * dZ1i * dZi2; // X
147 vGeant3[1] = vGeant3[1] + yPrime * dZ1i - 0.5 * ySecond * dZ1i * dZi2; // Y
148 vGeant3[2] = Z; // Z
149 Double_t xPrimeI = xPrime - 0.5 * xSecond * (dZi2 - dZ1i);
150 Double_t yPrimeI = yPrime - 0.5 * ySecond * (dZi2 - dZ1i);
956019b6 151 // (PX, PY, PZ)/PTOT assuming forward motion
a9e2aefa 152 vGeant3[5] =
153 1.0 / TMath::Sqrt(1.0 + xPrimeI * xPrimeI + yPrimeI * yPrimeI); // PZ/PTOT
154 vGeant3[3] = xPrimeI * vGeant3[5]; // PX/PTOT
155 vGeant3[4] = yPrimeI * vGeant3[5]; // PY/PTOT
956019b6 156 // Track parameters from Geant3 parameters,
157 // with charge back for forward motion
158 GetFromGeant3Parameters(vGeant3, chargeExtrap * forwardBackward);
a9e2aefa 159}
160
161 //__________________________________________________________________________
162void AliMUONTrackParam::SetGeant3Parameters(Double_t *VGeant3, Double_t ForwardBackward)
163{
164 // Set vector of Geant3 parameters pointed to by "VGeant3"
165 // from track parameters in current AliMUONTrackParam.
166 // Since AliMUONTrackParam is only geometry, one uses "ForwardBackward"
167 // to know whether the particle is going forward (+1) or backward (-1).
168 VGeant3[0] = this->fNonBendingCoor; // X
169 VGeant3[1] = this->fBendingCoor; // Y
170 VGeant3[2] = this->fZ; // Z
171 Double_t pYZ = TMath::Abs(1.0 / this->fInverseBendingMomentum);
172 Double_t pZ =
173 pYZ / TMath::Sqrt(1.0 + this->fBendingSlope * this->fBendingSlope);
174 VGeant3[6] =
175 TMath::Sqrt(pYZ * pYZ +
176 pZ * pZ * this->fNonBendingSlope * this->fNonBendingSlope); // PTOT
5b64e914 177 VGeant3[5] = -ForwardBackward * pZ / VGeant3[6]; // PZ/PTOT spectro. z<0
a9e2aefa 178 VGeant3[3] = this->fNonBendingSlope * VGeant3[5]; // PX/PTOT
179 VGeant3[4] = this->fBendingSlope * VGeant3[5]; // PY/PTOT
180}
181
182 //__________________________________________________________________________
183void AliMUONTrackParam::GetFromGeant3Parameters(Double_t *VGeant3, Double_t Charge)
184{
185 // Get track parameters in current AliMUONTrackParam
956019b6 186 // from Geant3 parameters pointed to by "VGeant3",
187 // assumed to be calculated for forward motion in Z.
a9e2aefa 188 // "InverseBendingMomentum" is signed with "Charge".
189 this->fNonBendingCoor = VGeant3[0]; // X
190 this->fBendingCoor = VGeant3[1]; // Y
191 this->fZ = VGeant3[2]; // Z
192 Double_t pYZ = VGeant3[6] * TMath::Sqrt(1.0 - VGeant3[3] * VGeant3[3]);
193 this->fInverseBendingMomentum = Charge / pYZ;
194 this->fBendingSlope = VGeant3[4] / VGeant3[5];
195 this->fNonBendingSlope = VGeant3[3] / VGeant3[5];
196}
197
198 //__________________________________________________________________________
199void AliMUONTrackParam::ExtrapToStation(Int_t Station, AliMUONTrackParam *TrackParam)
200{
201 // Track parameters extrapolated from current track parameters ("this")
202 // to both chambers of the station(0..) "Station"
203 // are returned in the array (dimension 2) of track parameters
204 // pointed to by "TrackParam" (index 0 and 1 for first and second chambers).
205 Double_t extZ[2], z1, z2;
ecfa008b 206 Int_t i1 = -1, i2 = -1; // = -1 to avoid compilation warnings
a9e2aefa 207 AliMUON *pMUON = (AliMUON*) gAlice->GetModule("MUON"); // necessary ????
208 // range of Station to be checked ????
209 z1 = (&(pMUON->Chamber(2 * Station)))->Z(); // Z of first chamber
210 z2 = (&(pMUON->Chamber(2 * Station + 1)))->Z(); // Z of second chamber
211 // First and second Z to extrapolate at
212 if ((z1 > this->fZ) && (z2 > this->fZ)) {i1 = 0; i2 = 1;}
213 else if ((z1 < this->fZ) && (z2 < this->fZ)) {i1 = 1; i2 = 0;}
214 else {
215 cout << "ERROR in AliMUONTrackParam::CreateExtrapSegmentInStation" << endl;
216 cout << "Starting Z (" << this->fZ << ") in between z1 (" << z1 <<
217 ") and z2 (" << z2 << ") of station(0..) " << Station << endl;
218 }
219 extZ[i1] = z1;
220 extZ[i2] = z2;
221 // copy of track parameters
222 TrackParam[i1] = *this;
223 // first extrapolation
224 (&(TrackParam[i1]))->ExtrapToZ(extZ[0]);
225 TrackParam[i2] = TrackParam[i1];
226 // second extrapolation
227 (&(TrackParam[i2]))->ExtrapToZ(extZ[1]);
228 return;
229}
230
04b5ea16 231 //__________________________________________________________________________
232void AliMUONTrackParam::ExtrapToVertex()
233{
234 // Extrapolation to the vertex.
235 // Returns the track parameters resulting from the extrapolation,
236 // in the current TrackParam.
956019b6 237 // Changes parameters according to Branson correction through the absorber
04b5ea16 238
5b64e914 239 Double_t zAbsorber = -503.0; // to be coherent with the Geant absorber geometry !!!!
240 // spectro. (z<0)
04b5ea16 241 // Extrapolates track parameters upstream to the "Z" end of the front absorber
b45fd22b 242 ExtrapToZ(zAbsorber); // !!!
5b64e914 243 // Makes Branson correction (multiple scattering + energy loss)
04b5ea16 244 BransonCorrection();
5b64e914 245 // Makes a simple magnetic field correction through the absorber
b45fd22b 246 FieldCorrection(zAbsorber);
04b5ea16 247}
248
43af2cb6 249
250// Keep this version for future developments
04b5ea16 251 //__________________________________________________________________________
43af2cb6 252// void AliMUONTrackParam::BransonCorrection()
253// {
254// // Branson correction of track parameters
255// // the entry parameters have to be calculated at the end of the absorber
256// Double_t zEndAbsorber, zBP, xBP, yBP;
257// Double_t pYZ, pX, pY, pZ, pTotal, xEndAbsorber, yEndAbsorber, radiusEndAbsorber2, pT, theta;
258// Int_t sign;
259// // Would it be possible to calculate all that from Geant configuration ????
260// // and to get the Branson parameters from a function in ABSO module ????
261// // with an eventual contribution from other detectors like START ????
262// // Radiation lengths outer part theta > 3 degres
263// static Double_t x01[9] = { 18.8, // C (cm)
264// 10.397, // Concrete (cm)
265// 0.56, // Plomb (cm)
266// 47.26, // Polyethylene (cm)
267// 0.56, // Plomb (cm)
268// 47.26, // Polyethylene (cm)
269// 0.56, // Plomb (cm)
270// 47.26, // Polyethylene (cm)
271// 0.56 }; // Plomb (cm)
272// // inner part theta < 3 degres
273// static Double_t x02[3] = { 18.8, // C (cm)
274// 10.397, // Concrete (cm)
275// 0.35 }; // W (cm)
276// // z positions of the materials inside the absober outer part theta > 3 degres
277// static Double_t z1[10] = { 90, 315, 467, 472, 477, 482, 487, 492, 497, 502 };
278// // inner part theta < 3 degres
279// static Double_t z2[4] = { 90, 315, 467, 503 };
280// static Bool_t first = kTRUE;
281// static Double_t zBP1, zBP2, rLimit;
282// // Calculates z positions of the Branson's planes: zBP1 for outer part and zBP2 for inner part (only at the first call)
283// if (first) {
284// first = kFALSE;
285// Double_t aNBP = 0.0;
286// Double_t aDBP = 0.0;
287// Int_t iBound;
288
289// for (iBound = 0; iBound < 9; iBound++) {
290// aNBP = aNBP +
291// (z1[iBound+1] * z1[iBound+1] * z1[iBound+1] -
292// z1[iBound] * z1[iBound] * z1[iBound] ) / x01[iBound];
293// aDBP = aDBP +
294// (z1[iBound+1] * z1[iBound+1] - z1[iBound] * z1[iBound] ) / x01[iBound];
295// }
296// zBP1 = (2.0 * aNBP) / (3.0 * aDBP);
297// aNBP = 0.0;
298// aDBP = 0.0;
299// for (iBound = 0; iBound < 3; iBound++) {
300// aNBP = aNBP +
301// (z2[iBound+1] * z2[iBound+1] * z2[iBound+1] -
302// z2[iBound] * z2[iBound ] * z2[iBound] ) / x02[iBound];
303// aDBP = aDBP +
304// (z2[iBound+1] * z2[iBound+1] - z2[iBound] * z2[iBound]) / x02[iBound];
305// }
306// zBP2 = (2.0 * aNBP) / (3.0 * aDBP);
307// rLimit = z2[3] * TMath::Tan(3.0 * (TMath::Pi()) / 180.);
308// }
309
310// pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
311// sign = 1;
312// if (fInverseBendingMomentum < 0) sign = -1;
313// pZ = pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope));
314// pX = pZ * fNonBendingSlope;
315// pY = pZ * fBendingSlope;
316// pTotal = TMath::Sqrt(pYZ *pYZ + pX * pX);
317// xEndAbsorber = fNonBendingCoor;
318// yEndAbsorber = fBendingCoor;
319// radiusEndAbsorber2 = xEndAbsorber * xEndAbsorber + yEndAbsorber * yEndAbsorber;
320
321// if (radiusEndAbsorber2 > rLimit*rLimit) {
322// zEndAbsorber = z1[9];
323// zBP = zBP1;
324// } else {
325// zEndAbsorber = z2[3];
326// zBP = zBP2;
327// }
328
329// xBP = xEndAbsorber - (pX / pZ) * (zEndAbsorber - zBP);
330// yBP = yEndAbsorber - (pY / pZ) * (zEndAbsorber - zBP);
331
332// // new parameters after Branson and energy loss corrections
333// pZ = pTotal * zBP / TMath::Sqrt(xBP * xBP + yBP * yBP + zBP * zBP);
334// pX = pZ * xBP / zBP;
335// pY = pZ * yBP / zBP;
336// fBendingSlope = pY / pZ;
337// fNonBendingSlope = pX / pZ;
338
339// pT = TMath::Sqrt(pX * pX + pY * pY);
340// theta = TMath::ATan2(pT, pZ);
341// pTotal =
342// TotalMomentumEnergyLoss(rLimit, pTotal, theta, xEndAbsorber, yEndAbsorber);
343
344// fInverseBendingMomentum = (sign / pTotal) *
345// TMath::Sqrt(1.0 +
346// fBendingSlope * fBendingSlope +
347// fNonBendingSlope * fNonBendingSlope) /
348// TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope);
349
350// // vertex position at (0,0,0)
351// // should be taken from vertex measurement ???
352// fBendingCoor = 0.0;
353// fNonBendingCoor = 0;
354// fZ= 0;
355// }
356
04b5ea16 357void AliMUONTrackParam::BransonCorrection()
358{
359 // Branson correction of track parameters
360 // the entry parameters have to be calculated at the end of the absorber
43af2cb6 361 // simplified version: the z positions of Branson's planes are no longer calculated
362 // but are given as inputs. One can use the macros MUONTestAbso.C and DrawTestAbso.C
363 // to test this correction.
04b5ea16 364 // Would it be possible to calculate all that from Geant configuration ????
956019b6 365 // and to get the Branson parameters from a function in ABSO module ????
366 // with an eventual contribution from other detectors like START ????
43af2cb6 367 Double_t zBP, xBP, yBP;
368 Double_t pYZ, pX, pY, pZ, pTotal, xEndAbsorber, yEndAbsorber, radiusEndAbsorber2, pT, theta;
369 Int_t sign;
04b5ea16 370 static Bool_t first = kTRUE;
b45fd22b 371 static Double_t zBP1, zBP2, rLimit, thetaLimit, zEndAbsorber;
43af2cb6 372 // zBP1 for outer part and zBP2 for inner part (only at the first call)
04b5ea16 373 if (first) {
374 first = kFALSE;
43af2cb6 375
5b64e914 376 zEndAbsorber = -503; // spectro (z<0)
b45fd22b 377 thetaLimit = 3.0 * (TMath::Pi()) / 180.;
5b64e914 378 rLimit = TMath::Abs(zEndAbsorber) * TMath::Tan(thetaLimit);
379 zBP1 = -450; // values close to those calculated with EvalAbso.C
380 zBP2 = -480;
04b5ea16 381 }
382
383 pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
384 sign = 1;
385 if (fInverseBendingMomentum < 0) sign = -1;
5b64e914 386 pZ = -pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope)); // spectro (z<0)
04b5ea16 387 pX = pZ * fNonBendingSlope;
388 pY = pZ * fBendingSlope;
389 pTotal = TMath::Sqrt(pYZ *pYZ + pX * pX);
390 xEndAbsorber = fNonBendingCoor;
391 yEndAbsorber = fBendingCoor;
392 radiusEndAbsorber2 = xEndAbsorber * xEndAbsorber + yEndAbsorber * yEndAbsorber;
393
394 if (radiusEndAbsorber2 > rLimit*rLimit) {
04b5ea16 395 zBP = zBP1;
396 } else {
04b5ea16 397 zBP = zBP2;
398 }
399
400 xBP = xEndAbsorber - (pX / pZ) * (zEndAbsorber - zBP);
401 yBP = yEndAbsorber - (pY / pZ) * (zEndAbsorber - zBP);
402
403 // new parameters after Branson and energy loss corrections
b45fd22b 404// Float_t zSmear = zBP - gRandom->Gaus(0.,2.); // !!! possible smearing of Z vertex position
405 Float_t zSmear = zBP;
406
407 pZ = pTotal * zSmear / TMath::Sqrt(xBP * xBP + yBP * yBP + zSmear * zSmear);
408 pX = pZ * xBP / zSmear;
409 pY = pZ * yBP / zSmear;
04b5ea16 410 fBendingSlope = pY / pZ;
411 fNonBendingSlope = pX / pZ;
5b64e914 412
04b5ea16 413
414 pT = TMath::Sqrt(pX * pX + pY * pY);
5b64e914 415 theta = TMath::ATan2(pT, TMath::Abs(pZ));
b45fd22b 416 pTotal = TotalMomentumEnergyLoss(thetaLimit, pTotal, theta);
04b5ea16 417
418 fInverseBendingMomentum = (sign / pTotal) *
419 TMath::Sqrt(1.0 +
420 fBendingSlope * fBendingSlope +
421 fNonBendingSlope * fNonBendingSlope) /
422 TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope);
423
424 // vertex position at (0,0,0)
425 // should be taken from vertex measurement ???
426 fBendingCoor = 0.0;
427 fNonBendingCoor = 0;
428 fZ= 0;
429}
b45fd22b 430
04b5ea16 431 //__________________________________________________________________________
b45fd22b 432Double_t AliMUONTrackParam::TotalMomentumEnergyLoss(Double_t thetaLimit, Double_t pTotal, Double_t theta)
04b5ea16 433{
434 // Returns the total momentum corrected from energy loss in the front absorber
43af2cb6 435 // One can use the macros MUONTestAbso.C and DrawTestAbso.C
436 // to test this correction.
b45fd22b 437 // Momentum energy loss behaviour evaluated with the simulation of single muons (april 2002)
04b5ea16 438 Double_t deltaP, pTotalCorrected;
439
b45fd22b 440 // Parametrization to be redone according to change of absorber material ????
956019b6 441 // See remark in function BransonCorrection !!!!
04b5ea16 442 // The name is not so good, and there are many arguments !!!!
b45fd22b 443 if (theta < thetaLimit ) {
444 if (pTotal < 20) {
445 deltaP = 2.5938 + 0.0570 * pTotal - 0.001151 * pTotal * pTotal;
04b5ea16 446 } else {
b45fd22b 447 deltaP = 3.0714 + 0.011767 *pTotal;
04b5ea16 448 }
449 } else {
b45fd22b 450 if (pTotal < 20) {
451 deltaP = 2.1207 + 0.05478 * pTotal - 0.00145079 * pTotal * pTotal;
04b5ea16 452 } else {
b45fd22b 453 deltaP = 2.6069 + 0.0051705 * pTotal;
04b5ea16 454 }
455 }
456 pTotalCorrected = pTotal + deltaP / TMath::Cos(theta);
457 return pTotalCorrected;
458}
459
b45fd22b 460 //__________________________________________________________________________
461void AliMUONTrackParam::FieldCorrection(Double_t Z)
462{
463 //
464 // Correction of the effect of the magnetic field in the absorber
465 // Assume a constant field along Z axis.
466
467 Float_t b[3],x[3];
468 Double_t bZ;
469 Double_t pYZ,pX,pY,pZ,pT;
470 Double_t pXNew,pYNew;
471 Double_t c;
472
473 pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
474 c = TMath::Sign(1.0,fInverseBendingMomentum); // particle charge
475
5b64e914 476 pZ = -pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope)); // spectro. (z<0)
b45fd22b 477 pX = pZ * fNonBendingSlope;
478 pY = pZ * fBendingSlope;
479 pT = TMath::Sqrt(pX*pX+pY*pY);
480
5b64e914 481 if (TMath::Abs(pZ) <= 0) return;
b45fd22b 482 x[2] = Z/2;
483 x[0] = x[2]*fNonBendingSlope;
484 x[1] = x[2]*fBendingSlope;
485
486 // Take magn. field value at position x.
487 gAlice->Field()->Field(x, b);
488 bZ = b[2];
489
490 // Transverse momentum rotation
491 // Parameterized with the study of DeltaPhi = phiReco - phiGen as a function of pZ.
5b64e914 492 Double_t phiShift = c*0.436*0.0003*bZ*Z/pZ;
b45fd22b 493 // Rotate momentum around Z axis.
494 pXNew = pX*TMath::Cos(phiShift) - pY*TMath::Sin(phiShift);
495 pYNew = pX*TMath::Sin(phiShift) + pY*TMath::Cos(phiShift);
496
497 fBendingSlope = pYNew / pZ;
498 fNonBendingSlope = pXNew / pZ;
499
500 fInverseBendingMomentum = c / TMath::Sqrt(pYNew*pYNew+pZ*pZ);
501
502}