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Convert fortran functions into C (Christian)
[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>
3831f268 29#include "AliMUON.h"
a9e2aefa 30#include "AliMUONTrackParam.h"
3831f268 31#include "AliMUONChamber.h"
a9e2aefa 32#include "AliRun.h"
94de3818 33#include "AliMagF.h"
8c343c7c 34#include "AliLog.h"
a9e2aefa 35
36ClassImp(AliMUONTrackParam) // Class implementation in ROOT context
37
61adb9bd 38 //_________________________________________________________________________
30178c30 39AliMUONTrackParam::AliMUONTrackParam()
40 : TObject()
41{
42// Constructor
43
44 fInverseBendingMomentum = 0;
45 fBendingSlope = 0;
46 fNonBendingSlope = 0;
47 fZ = 0;
48 fBendingCoor = 0;
49 fNonBendingCoor = 0;
50}
61adb9bd 51
30178c30 52 //_________________________________________________________________________
53AliMUONTrackParam&
54AliMUONTrackParam::operator=(const AliMUONTrackParam& theMUONTrackParam)
61adb9bd 55{
30178c30 56 if (this == &theMUONTrackParam)
61adb9bd 57 return *this;
58
30178c30 59 // base class assignement
60 TObject::operator=(theMUONTrackParam);
61
62 fInverseBendingMomentum = theMUONTrackParam.fInverseBendingMomentum;
63 fBendingSlope = theMUONTrackParam.fBendingSlope;
64 fNonBendingSlope = theMUONTrackParam.fNonBendingSlope;
65 fZ = theMUONTrackParam.fZ;
66 fBendingCoor = theMUONTrackParam.fBendingCoor;
67 fNonBendingCoor = theMUONTrackParam.fNonBendingCoor;
61adb9bd 68
69 return *this;
70}
71 //_________________________________________________________________________
30178c30 72AliMUONTrackParam::AliMUONTrackParam(const AliMUONTrackParam& theMUONTrackParam)
73 : TObject(theMUONTrackParam)
61adb9bd 74{
30178c30 75 fInverseBendingMomentum = theMUONTrackParam.fInverseBendingMomentum;
76 fBendingSlope = theMUONTrackParam.fBendingSlope;
77 fNonBendingSlope = theMUONTrackParam.fNonBendingSlope;
78 fZ = theMUONTrackParam.fZ;
79 fBendingCoor = theMUONTrackParam.fBendingCoor;
80 fNonBendingCoor = theMUONTrackParam.fNonBendingCoor;
61adb9bd 81}
a9e2aefa 82
a9e2aefa 83 //__________________________________________________________________________
84void AliMUONTrackParam::ExtrapToZ(Double_t Z)
85{
86 // Track parameter extrapolation to the plane at "Z".
87 // On return, the track parameters resulting from the extrapolation
88 // replace the current track parameters.
a9e2aefa 89 if (this->fZ == Z) return; // nothing to be done if same Z
90 Double_t forwardBackward; // +1 if forward, -1 if backward
5b64e914 91 if (Z < this->fZ) forwardBackward = 1.0; // spectro. z<0
a9e2aefa 92 else forwardBackward = -1.0;
a6f03ddb 93 Double_t vGeant3[7], vGeant3New[7]; // 7 in parameter ????
a9e2aefa 94 Int_t iGeant3, stepNumber;
95 Int_t maxStepNumber = 5000; // in parameter ????
96 // For safety: return kTRUE or kFALSE ????
a6f03ddb 97 // Parameter vector for calling EXTRAP_ONESTEP
a9e2aefa 98 SetGeant3Parameters(vGeant3, forwardBackward);
956019b6 99 // sign of charge (sign of fInverseBendingMomentum if forward motion)
a6f03ddb 100 // must be changed if backward extrapolation
956019b6 101 Double_t chargeExtrap = forwardBackward *
102 TMath::Sign(Double_t(1.0), this->fInverseBendingMomentum);
a9e2aefa 103 Double_t stepLength = 6.0; // in parameter ????
104 // Extrapolation loop
105 stepNumber = 0;
5b64e914 106 while (((-forwardBackward * (vGeant3[2] - Z)) <= 0.0) && // spectro. z<0
a9e2aefa 107 (stepNumber < maxStepNumber)) {
108 stepNumber++;
a6f03ddb 109 // Option for switching between helix and Runge-Kutta ????
4d03a78e 110 //ExtrapOneStepRungekutta(chargeExtrap, stepLength, vGeant3, vGeant3New);
111 ExtrapOneStepHelix(chargeExtrap, stepLength, vGeant3, vGeant3New);
5b64e914 112 if ((-forwardBackward * (vGeant3New[2] - Z)) > 0.0) break; // one is beyond Z spectro. z<0
a9e2aefa 113 // better use TArray ????
114 for (iGeant3 = 0; iGeant3 < 7; iGeant3++)
115 {vGeant3[iGeant3] = vGeant3New[iGeant3];}
116 }
117 // check maxStepNumber ????
a9e2aefa 118 // Interpolation back to exact Z (2nd order)
119 // should be in function ???? using TArray ????
120 Double_t dZ12 = vGeant3New[2] - vGeant3[2]; // 1->2
121 Double_t dZ1i = Z - vGeant3[2]; // 1-i
122 Double_t dZi2 = vGeant3New[2] - Z; // i->2
123 Double_t xPrime = (vGeant3New[0] - vGeant3[0]) / dZ12;
124 Double_t xSecond =
125 ((vGeant3New[3] / vGeant3New[5]) - (vGeant3[3] / vGeant3[5])) / dZ12;
126 Double_t yPrime = (vGeant3New[1] - vGeant3[1]) / dZ12;
127 Double_t ySecond =
128 ((vGeant3New[4] / vGeant3New[5]) - (vGeant3[4] / vGeant3[5])) / dZ12;
129 vGeant3[0] = vGeant3[0] + xPrime * dZ1i - 0.5 * xSecond * dZ1i * dZi2; // X
130 vGeant3[1] = vGeant3[1] + yPrime * dZ1i - 0.5 * ySecond * dZ1i * dZi2; // Y
131 vGeant3[2] = Z; // Z
132 Double_t xPrimeI = xPrime - 0.5 * xSecond * (dZi2 - dZ1i);
133 Double_t yPrimeI = yPrime - 0.5 * ySecond * (dZi2 - dZ1i);
956019b6 134 // (PX, PY, PZ)/PTOT assuming forward motion
a9e2aefa 135 vGeant3[5] =
136 1.0 / TMath::Sqrt(1.0 + xPrimeI * xPrimeI + yPrimeI * yPrimeI); // PZ/PTOT
137 vGeant3[3] = xPrimeI * vGeant3[5]; // PX/PTOT
138 vGeant3[4] = yPrimeI * vGeant3[5]; // PY/PTOT
956019b6 139 // Track parameters from Geant3 parameters,
140 // with charge back for forward motion
141 GetFromGeant3Parameters(vGeant3, chargeExtrap * forwardBackward);
a9e2aefa 142}
143
144 //__________________________________________________________________________
145void AliMUONTrackParam::SetGeant3Parameters(Double_t *VGeant3, Double_t ForwardBackward)
146{
147 // Set vector of Geant3 parameters pointed to by "VGeant3"
148 // from track parameters in current AliMUONTrackParam.
149 // Since AliMUONTrackParam is only geometry, one uses "ForwardBackward"
150 // to know whether the particle is going forward (+1) or backward (-1).
151 VGeant3[0] = this->fNonBendingCoor; // X
152 VGeant3[1] = this->fBendingCoor; // Y
153 VGeant3[2] = this->fZ; // Z
154 Double_t pYZ = TMath::Abs(1.0 / this->fInverseBendingMomentum);
155 Double_t pZ =
156 pYZ / TMath::Sqrt(1.0 + this->fBendingSlope * this->fBendingSlope);
157 VGeant3[6] =
158 TMath::Sqrt(pYZ * pYZ +
159 pZ * pZ * this->fNonBendingSlope * this->fNonBendingSlope); // PTOT
5b64e914 160 VGeant3[5] = -ForwardBackward * pZ / VGeant3[6]; // PZ/PTOT spectro. z<0
a9e2aefa 161 VGeant3[3] = this->fNonBendingSlope * VGeant3[5]; // PX/PTOT
162 VGeant3[4] = this->fBendingSlope * VGeant3[5]; // PY/PTOT
163}
164
165 //__________________________________________________________________________
166void AliMUONTrackParam::GetFromGeant3Parameters(Double_t *VGeant3, Double_t Charge)
167{
168 // Get track parameters in current AliMUONTrackParam
956019b6 169 // from Geant3 parameters pointed to by "VGeant3",
170 // assumed to be calculated for forward motion in Z.
a9e2aefa 171 // "InverseBendingMomentum" is signed with "Charge".
172 this->fNonBendingCoor = VGeant3[0]; // X
173 this->fBendingCoor = VGeant3[1]; // Y
174 this->fZ = VGeant3[2]; // Z
175 Double_t pYZ = VGeant3[6] * TMath::Sqrt(1.0 - VGeant3[3] * VGeant3[3]);
176 this->fInverseBendingMomentum = Charge / pYZ;
177 this->fBendingSlope = VGeant3[4] / VGeant3[5];
178 this->fNonBendingSlope = VGeant3[3] / VGeant3[5];
179}
180
181 //__________________________________________________________________________
182void AliMUONTrackParam::ExtrapToStation(Int_t Station, AliMUONTrackParam *TrackParam)
183{
184 // Track parameters extrapolated from current track parameters ("this")
185 // to both chambers of the station(0..) "Station"
186 // are returned in the array (dimension 2) of track parameters
187 // pointed to by "TrackParam" (index 0 and 1 for first and second chambers).
188 Double_t extZ[2], z1, z2;
ecfa008b 189 Int_t i1 = -1, i2 = -1; // = -1 to avoid compilation warnings
a9e2aefa 190 AliMUON *pMUON = (AliMUON*) gAlice->GetModule("MUON"); // necessary ????
191 // range of Station to be checked ????
192 z1 = (&(pMUON->Chamber(2 * Station)))->Z(); // Z of first chamber
193 z2 = (&(pMUON->Chamber(2 * Station + 1)))->Z(); // Z of second chamber
194 // First and second Z to extrapolate at
195 if ((z1 > this->fZ) && (z2 > this->fZ)) {i1 = 0; i2 = 1;}
196 else if ((z1 < this->fZ) && (z2 < this->fZ)) {i1 = 1; i2 = 0;}
197 else {
8c343c7c 198 AliError(Form("Starting Z (%f) in between z1 (%f) and z2 (%f) of station(0..)%d",this->fZ,z1,z2,Station));
199// cout << "ERROR in AliMUONTrackParam::CreateExtrapSegmentInStation" << endl;
200// cout << "Starting Z (" << this->fZ << ") in between z1 (" << z1 <<
201// ") and z2 (" << z2 << ") of station(0..) " << Station << endl;
a9e2aefa 202 }
203 extZ[i1] = z1;
204 extZ[i2] = z2;
205 // copy of track parameters
206 TrackParam[i1] = *this;
207 // first extrapolation
208 (&(TrackParam[i1]))->ExtrapToZ(extZ[0]);
209 TrackParam[i2] = TrackParam[i1];
210 // second extrapolation
211 (&(TrackParam[i2]))->ExtrapToZ(extZ[1]);
212 return;
213}
214
04b5ea16 215 //__________________________________________________________________________
889a0215 216void AliMUONTrackParam::ExtrapToVertex(Double_t xVtx, Double_t yVtx, Double_t zVtx)
04b5ea16 217{
218 // Extrapolation to the vertex.
219 // Returns the track parameters resulting from the extrapolation,
220 // in the current TrackParam.
956019b6 221 // Changes parameters according to Branson correction through the absorber
04b5ea16 222
5b64e914 223 Double_t zAbsorber = -503.0; // to be coherent with the Geant absorber geometry !!!!
224 // spectro. (z<0)
04b5ea16 225 // Extrapolates track parameters upstream to the "Z" end of the front absorber
b45fd22b 226 ExtrapToZ(zAbsorber); // !!!
5b64e914 227 // Makes Branson correction (multiple scattering + energy loss)
889a0215 228 BransonCorrection(xVtx,yVtx,zVtx);
5b64e914 229 // Makes a simple magnetic field correction through the absorber
b45fd22b 230 FieldCorrection(zAbsorber);
04b5ea16 231}
232
43af2cb6 233
234// Keep this version for future developments
04b5ea16 235 //__________________________________________________________________________
43af2cb6 236// void AliMUONTrackParam::BransonCorrection()
237// {
238// // Branson correction of track parameters
239// // the entry parameters have to be calculated at the end of the absorber
240// Double_t zEndAbsorber, zBP, xBP, yBP;
241// Double_t pYZ, pX, pY, pZ, pTotal, xEndAbsorber, yEndAbsorber, radiusEndAbsorber2, pT, theta;
242// Int_t sign;
243// // Would it be possible to calculate all that from Geant configuration ????
244// // and to get the Branson parameters from a function in ABSO module ????
245// // with an eventual contribution from other detectors like START ????
246// // Radiation lengths outer part theta > 3 degres
247// static Double_t x01[9] = { 18.8, // C (cm)
248// 10.397, // Concrete (cm)
249// 0.56, // Plomb (cm)
250// 47.26, // Polyethylene (cm)
251// 0.56, // Plomb (cm)
252// 47.26, // Polyethylene (cm)
253// 0.56, // Plomb (cm)
254// 47.26, // Polyethylene (cm)
255// 0.56 }; // Plomb (cm)
256// // inner part theta < 3 degres
257// static Double_t x02[3] = { 18.8, // C (cm)
258// 10.397, // Concrete (cm)
259// 0.35 }; // W (cm)
260// // z positions of the materials inside the absober outer part theta > 3 degres
261// static Double_t z1[10] = { 90, 315, 467, 472, 477, 482, 487, 492, 497, 502 };
262// // inner part theta < 3 degres
263// static Double_t z2[4] = { 90, 315, 467, 503 };
264// static Bool_t first = kTRUE;
265// static Double_t zBP1, zBP2, rLimit;
266// // Calculates z positions of the Branson's planes: zBP1 for outer part and zBP2 for inner part (only at the first call)
267// if (first) {
268// first = kFALSE;
269// Double_t aNBP = 0.0;
270// Double_t aDBP = 0.0;
271// Int_t iBound;
272
273// for (iBound = 0; iBound < 9; iBound++) {
274// aNBP = aNBP +
275// (z1[iBound+1] * z1[iBound+1] * z1[iBound+1] -
276// z1[iBound] * z1[iBound] * z1[iBound] ) / x01[iBound];
277// aDBP = aDBP +
278// (z1[iBound+1] * z1[iBound+1] - z1[iBound] * z1[iBound] ) / x01[iBound];
279// }
280// zBP1 = (2.0 * aNBP) / (3.0 * aDBP);
281// aNBP = 0.0;
282// aDBP = 0.0;
283// for (iBound = 0; iBound < 3; iBound++) {
284// aNBP = aNBP +
285// (z2[iBound+1] * z2[iBound+1] * z2[iBound+1] -
286// z2[iBound] * z2[iBound ] * z2[iBound] ) / x02[iBound];
287// aDBP = aDBP +
288// (z2[iBound+1] * z2[iBound+1] - z2[iBound] * z2[iBound]) / x02[iBound];
289// }
290// zBP2 = (2.0 * aNBP) / (3.0 * aDBP);
291// rLimit = z2[3] * TMath::Tan(3.0 * (TMath::Pi()) / 180.);
292// }
293
294// pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
295// sign = 1;
296// if (fInverseBendingMomentum < 0) sign = -1;
297// pZ = pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope));
298// pX = pZ * fNonBendingSlope;
299// pY = pZ * fBendingSlope;
300// pTotal = TMath::Sqrt(pYZ *pYZ + pX * pX);
301// xEndAbsorber = fNonBendingCoor;
302// yEndAbsorber = fBendingCoor;
303// radiusEndAbsorber2 = xEndAbsorber * xEndAbsorber + yEndAbsorber * yEndAbsorber;
304
305// if (radiusEndAbsorber2 > rLimit*rLimit) {
306// zEndAbsorber = z1[9];
307// zBP = zBP1;
308// } else {
309// zEndAbsorber = z2[3];
310// zBP = zBP2;
311// }
312
313// xBP = xEndAbsorber - (pX / pZ) * (zEndAbsorber - zBP);
314// yBP = yEndAbsorber - (pY / pZ) * (zEndAbsorber - zBP);
315
316// // new parameters after Branson and energy loss corrections
317// pZ = pTotal * zBP / TMath::Sqrt(xBP * xBP + yBP * yBP + zBP * zBP);
318// pX = pZ * xBP / zBP;
319// pY = pZ * yBP / zBP;
320// fBendingSlope = pY / pZ;
321// fNonBendingSlope = pX / pZ;
322
323// pT = TMath::Sqrt(pX * pX + pY * pY);
324// theta = TMath::ATan2(pT, pZ);
325// pTotal =
326// TotalMomentumEnergyLoss(rLimit, pTotal, theta, xEndAbsorber, yEndAbsorber);
327
328// fInverseBendingMomentum = (sign / pTotal) *
329// TMath::Sqrt(1.0 +
330// fBendingSlope * fBendingSlope +
331// fNonBendingSlope * fNonBendingSlope) /
332// TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope);
333
334// // vertex position at (0,0,0)
335// // should be taken from vertex measurement ???
336// fBendingCoor = 0.0;
337// fNonBendingCoor = 0;
338// fZ= 0;
339// }
340
889a0215 341void AliMUONTrackParam::BransonCorrection(Double_t xVtx,Double_t yVtx,Double_t zVtx)
04b5ea16 342{
343 // Branson correction of track parameters
344 // the entry parameters have to be calculated at the end of the absorber
43af2cb6 345 // simplified version: the z positions of Branson's planes are no longer calculated
346 // but are given as inputs. One can use the macros MUONTestAbso.C and DrawTestAbso.C
347 // to test this correction.
04b5ea16 348 // Would it be possible to calculate all that from Geant configuration ????
956019b6 349 // and to get the Branson parameters from a function in ABSO module ????
350 // with an eventual contribution from other detectors like START ????
889a0215 351 //change to take into account the vertex postition (real, reconstruct,....)
352
43af2cb6 353 Double_t zBP, xBP, yBP;
354 Double_t pYZ, pX, pY, pZ, pTotal, xEndAbsorber, yEndAbsorber, radiusEndAbsorber2, pT, theta;
355 Int_t sign;
04b5ea16 356 static Bool_t first = kTRUE;
b45fd22b 357 static Double_t zBP1, zBP2, rLimit, thetaLimit, zEndAbsorber;
43af2cb6 358 // zBP1 for outer part and zBP2 for inner part (only at the first call)
04b5ea16 359 if (first) {
360 first = kFALSE;
43af2cb6 361
5b64e914 362 zEndAbsorber = -503; // spectro (z<0)
b45fd22b 363 thetaLimit = 3.0 * (TMath::Pi()) / 180.;
5b64e914 364 rLimit = TMath::Abs(zEndAbsorber) * TMath::Tan(thetaLimit);
365 zBP1 = -450; // values close to those calculated with EvalAbso.C
366 zBP2 = -480;
04b5ea16 367 }
368
369 pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
370 sign = 1;
b8dc484b 371 if (fInverseBendingMomentum < 0) sign = -1;
372 pZ = Pz();
373 pX = Px();
374 pY = Py();
04b5ea16 375 pTotal = TMath::Sqrt(pYZ *pYZ + pX * pX);
376 xEndAbsorber = fNonBendingCoor;
377 yEndAbsorber = fBendingCoor;
378 radiusEndAbsorber2 = xEndAbsorber * xEndAbsorber + yEndAbsorber * yEndAbsorber;
379
380 if (radiusEndAbsorber2 > rLimit*rLimit) {
04b5ea16 381 zBP = zBP1;
382 } else {
04b5ea16 383 zBP = zBP2;
384 }
385
386 xBP = xEndAbsorber - (pX / pZ) * (zEndAbsorber - zBP);
387 yBP = yEndAbsorber - (pY / pZ) * (zEndAbsorber - zBP);
388
389 // new parameters after Branson and energy loss corrections
b45fd22b 390// Float_t zSmear = zBP - gRandom->Gaus(0.,2.); // !!! possible smearing of Z vertex position
889a0215 391
392 Float_t zSmear = zBP ;
b45fd22b 393
889a0215 394 pZ = pTotal * (zSmear-zVtx) / TMath::Sqrt((xBP-xVtx) * (xBP-xVtx) + (yBP-yVtx) * (yBP-yVtx) +( zSmear-zVtx) * (zSmear-zVtx) );
395 pX = pZ * (xBP - xVtx)/ (zSmear-zVtx);
396 pY = pZ * (yBP - yVtx) / (zSmear-zVtx);
04b5ea16 397 fBendingSlope = pY / pZ;
398 fNonBendingSlope = pX / pZ;
5b64e914 399
04b5ea16 400
401 pT = TMath::Sqrt(pX * pX + pY * pY);
5b64e914 402 theta = TMath::ATan2(pT, TMath::Abs(pZ));
b45fd22b 403 pTotal = TotalMomentumEnergyLoss(thetaLimit, pTotal, theta);
04b5ea16 404
405 fInverseBendingMomentum = (sign / pTotal) *
406 TMath::Sqrt(1.0 +
407 fBendingSlope * fBendingSlope +
408 fNonBendingSlope * fNonBendingSlope) /
409 TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope);
410
411 // vertex position at (0,0,0)
412 // should be taken from vertex measurement ???
889a0215 413
414 fBendingCoor = xVtx;
415 fNonBendingCoor = yVtx;
416 fZ= zVtx;
417
04b5ea16 418}
b45fd22b 419
04b5ea16 420 //__________________________________________________________________________
b45fd22b 421Double_t AliMUONTrackParam::TotalMomentumEnergyLoss(Double_t thetaLimit, Double_t pTotal, Double_t theta)
04b5ea16 422{
423 // Returns the total momentum corrected from energy loss in the front absorber
43af2cb6 424 // One can use the macros MUONTestAbso.C and DrawTestAbso.C
425 // to test this correction.
b45fd22b 426 // Momentum energy loss behaviour evaluated with the simulation of single muons (april 2002)
04b5ea16 427 Double_t deltaP, pTotalCorrected;
428
b45fd22b 429 // Parametrization to be redone according to change of absorber material ????
956019b6 430 // See remark in function BransonCorrection !!!!
04b5ea16 431 // The name is not so good, and there are many arguments !!!!
b45fd22b 432 if (theta < thetaLimit ) {
433 if (pTotal < 20) {
434 deltaP = 2.5938 + 0.0570 * pTotal - 0.001151 * pTotal * pTotal;
04b5ea16 435 } else {
b45fd22b 436 deltaP = 3.0714 + 0.011767 *pTotal;
04b5ea16 437 }
438 } else {
b45fd22b 439 if (pTotal < 20) {
440 deltaP = 2.1207 + 0.05478 * pTotal - 0.00145079 * pTotal * pTotal;
04b5ea16 441 } else {
b45fd22b 442 deltaP = 2.6069 + 0.0051705 * pTotal;
04b5ea16 443 }
444 }
445 pTotalCorrected = pTotal + deltaP / TMath::Cos(theta);
446 return pTotalCorrected;
447}
448
b45fd22b 449 //__________________________________________________________________________
450void AliMUONTrackParam::FieldCorrection(Double_t Z)
451{
452 //
453 // Correction of the effect of the magnetic field in the absorber
454 // Assume a constant field along Z axis.
455
456 Float_t b[3],x[3];
457 Double_t bZ;
458 Double_t pYZ,pX,pY,pZ,pT;
459 Double_t pXNew,pYNew;
460 Double_t c;
461
462 pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
463 c = TMath::Sign(1.0,fInverseBendingMomentum); // particle charge
464
b8dc484b 465 pZ = Pz();
466 pX = Px();
467 pY = Py();
b45fd22b 468 pT = TMath::Sqrt(pX*pX+pY*pY);
469
5b64e914 470 if (TMath::Abs(pZ) <= 0) return;
b45fd22b 471 x[2] = Z/2;
472 x[0] = x[2]*fNonBendingSlope;
473 x[1] = x[2]*fBendingSlope;
474
475 // Take magn. field value at position x.
476 gAlice->Field()->Field(x, b);
477 bZ = b[2];
478
479 // Transverse momentum rotation
480 // Parameterized with the study of DeltaPhi = phiReco - phiGen as a function of pZ.
5b64e914 481 Double_t phiShift = c*0.436*0.0003*bZ*Z/pZ;
b45fd22b 482 // Rotate momentum around Z axis.
483 pXNew = pX*TMath::Cos(phiShift) - pY*TMath::Sin(phiShift);
484 pYNew = pX*TMath::Sin(phiShift) + pY*TMath::Cos(phiShift);
485
486 fBendingSlope = pYNew / pZ;
487 fNonBendingSlope = pXNew / pZ;
488
489 fInverseBendingMomentum = c / TMath::Sqrt(pYNew*pYNew+pZ*pZ);
490
b8dc484b 491}
492 //__________________________________________________________________________
493Double_t AliMUONTrackParam::Px()
494{
495 // return px from track paramaters
496 Double_t pYZ, pZ, pX;
497 pYZ = 0;
498 if ( TMath::Abs(fInverseBendingMomentum) > 0 )
499 pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
500 pZ = -pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope)); // spectro. (z<0)
501 pX = pZ * fNonBendingSlope;
502 return pX;
503}
504 //__________________________________________________________________________
505Double_t AliMUONTrackParam::Py()
506{
507 // return px from track paramaters
508 Double_t pYZ, pZ, pY;
509 pYZ = 0;
510 if ( TMath::Abs(fInverseBendingMomentum) > 0 )
511 pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
512 pZ = -pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope)); // spectro. (z<0)
513 pY = pZ * fBendingSlope;
514 return pY;
515}
516 //__________________________________________________________________________
517Double_t AliMUONTrackParam::Pz()
518{
519 // return px from track paramaters
520 Double_t pYZ, pZ;
521 pYZ = 0;
522 if ( TMath::Abs(fInverseBendingMomentum) > 0 )
523 pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
524 pZ = -pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope)); // spectro. (z<0)
525 return pZ;
526}
527 //__________________________________________________________________________
528Double_t AliMUONTrackParam::P()
529{
530 // return p from track paramaters
531 Double_t pYZ, pZ, p;
532 pYZ = 0;
533 if ( TMath::Abs(fInverseBendingMomentum) > 0 )
534 pYZ = TMath::Abs(1.0 / fInverseBendingMomentum);
535 pZ = -pYZ / (TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope)); // spectro. (z<0)
536 p = TMath::Abs(pZ) *
537 TMath::Sqrt(1.0 + fBendingSlope * fBendingSlope + fNonBendingSlope * fNonBendingSlope);
538 return p;
539
b45fd22b 540}
4d03a78e 541 //__________________________________________________________________________
542void AliMUONTrackParam::ExtrapOneStepHelix(Double_t charge, Double_t step,
543 Double_t *vect, Double_t *vout)
544{
545// ******************************************************************
546// * *
547// * Performs the tracking of one step in a magnetic field *
548// * The trajectory is assumed to be a helix in a constant field *
549// * taken at the mid point of the step. *
550// * Parameters: *
551// * input *
552// * STEP =arc length of the step asked *
553// * VECT =input vector (position,direction cos and momentum) *
554// * CHARGE= electric charge of the particle *
555// * output *
556// * VOUT = same as VECT after completion of the step *
557// * *
558// * ==>Called by : <USER>, GUSWIM *
559// * Author m.hansroul ********* *
560// * modified s.egli, s.v.levonian *
561// * modified v.perevoztchikov
562// * *
563// ******************************************************************
564//
565
566// modif: everything in double precision
567
568 Double_t xyz[3], h[4], hxp[3];
569 Double_t h2xy, hp, rho, tet;
570 Double_t sint, sintt, tsint, cos1t;
571 Double_t f1, f2, f3, f4, f5, f6;
572
573 const Int_t ix = 0;
574 const Int_t iy = 1;
575 const Int_t iz = 2;
576 const Int_t ipx = 3;
577 const Int_t ipy = 4;
578 const Int_t ipz = 5;
579 const Int_t ipp = 6;
580
581 const Double_t ec = 2.9979251e-4;
582 //
583 // ------------------------------------------------------------------
584 //
585 // units are kgauss,centimeters,gev/c
586 //
587 vout[ipp] = vect[ipp];
588 if (TMath::Abs(charge) < 0.00001) {
589 for (Int_t i = 0; i < 3; i++) {
590 vout[i] = vect[i] + step * vect[i+3];
591 vout[i+3] = vect[i+3];
592 }
593 return;
594 }
595 xyz[0] = vect[ix] + 0.5 * step * vect[ipx];
596 xyz[1] = vect[iy] + 0.5 * step * vect[ipy];
597 xyz[2] = vect[iz] + 0.5 * step * vect[ipz];
598
599 //cmodif: call gufld (xyz, h) changed into:
600 GetField (xyz, h);
601
602 h2xy = h[0]*h[0] + h[1]*h[1];
603 h[3] = h[2]*h[2]+ h2xy;
604 if (h[3] < 1.e-12) {
605 for (Int_t i = 0; i < 3; i++) {
606 vout[i] = vect[i] + step * vect[i+3];
607 vout[i+3] = vect[i+3];
608 }
609 return;
610 }
611 if (h2xy < 1.e-12*h[3]) {
612 ExtrapOneStepHelix3(charge*h[2], step, vect, vout);
613 return;
614 }
615 h[3] = TMath::Sqrt(h[3]);
616 h[0] /= h[3];
617 h[1] /= h[3];
618 h[2] /= h[3];
619 h[3] *= ec;
620
621 hxp[0] = h[1]*vect[ipz] - h[2]*vect[ipy];
622 hxp[1] = h[2]*vect[ipx] - h[0]*vect[ipz];
623 hxp[2] = h[0]*vect[ipy] - h[1]*vect[ipx];
624
625 hp = h[0]*vect[ipx] + h[1]*vect[ipy] + h[2]*vect[ipz];
626
627 rho = -charge*h[3]/vect[ipp];
628 tet = rho * step;
629
630 if (TMath::Abs(tet) > 0.15) {
631 sint = TMath::Sin(tet);
632 sintt = (sint/tet);
633 tsint = (tet-sint)/tet;
634 cos1t = 2.*(TMath::Sin(0.5*tet))*(TMath::Sin(0.5*tet))/tet;
635 } else {
636 tsint = tet*tet/36.;
637 sintt = (1. - tsint);
638 sint = tet*sintt;
639 cos1t = 0.5*tet;
640 }
641
642 f1 = step * sintt;
643 f2 = step * cos1t;
644 f3 = step * tsint * hp;
645 f4 = -tet*cos1t;
646 f5 = sint;
647 f6 = tet * cos1t * hp;
648
649 vout[ix] = vect[ix] + f1*vect[ipx] + f2*hxp[0] + f3*h[0];
650 vout[iy] = vect[iy] + f1*vect[ipy] + f2*hxp[1] + f3*h[1];
651 vout[iz] = vect[iz] + f1*vect[ipz] + f2*hxp[2] + f3*h[2];
652
653 vout[ipx] = vect[ipx] + f4*vect[ipx] + f5*hxp[0] + f6*h[0];
654 vout[ipy] = vect[ipy] + f4*vect[ipy] + f5*hxp[1] + f6*h[1];
655 vout[ipz] = vect[ipz] + f4*vect[ipz] + f5*hxp[2] + f6*h[2];
656
657 return;
658}
659
660 //__________________________________________________________________________
661void AliMUONTrackParam::ExtrapOneStepHelix3(Double_t field, Double_t step,
662 Double_t *vect, Double_t *vout)
663{
664//
665// ******************************************************************
666// * *
667// * Tracking routine in a constant field oriented *
668// * along axis 3 *
669// * Tracking is performed with a conventional *
670// * helix step method *
671// * *
672// * ==>Called by : <USER>, GUSWIM *
673// * Authors R.Brun, M.Hansroul ********* *
674// * Rewritten V.Perevoztchikov
675// * *
676// ******************************************************************
677//
678
679 Double_t hxp[3];
680 Double_t h4, hp, rho, tet;
681 Double_t sint, sintt, tsint, cos1t;
682 Double_t f1, f2, f3, f4, f5, f6;
683
684 const Int_t ix = 0;
685 const Int_t iy = 1;
686 const Int_t iz = 2;
687 const Int_t ipx = 3;
688 const Int_t ipy = 4;
689 const Int_t ipz = 5;
690 const Int_t ipp = 6;
691
692 const Double_t ec = 2.9979251e-4;
693
694//
695// ------------------------------------------------------------------
696//
697// units are kgauss,centimeters,gev/c
698//
699 vout[ipp] = vect[ipp];
700 h4 = field * ec;
701
702 hxp[0] = - vect[ipy];
703 hxp[1] = + vect[ipx];
704
705 hp = vect[ipz];
706
707 rho = -h4/vect[ipp];
708 tet = rho * step;
709 if (TMath::Abs(tet) > 0.15) {
710 sint = TMath::Sin(tet);
711 sintt = (sint/tet);
712 tsint = (tet-sint)/tet;
713 cos1t = 2.* TMath::Sin(0.5*tet) * TMath::Sin(0.5*tet)/tet;
714 } else {
715 tsint = tet*tet/36.;
716 sintt = (1. - tsint);
717 sint = tet*sintt;
718 cos1t = 0.5*tet;
719 }
720
721 f1 = step * sintt;
722 f2 = step * cos1t;
723 f3 = step * tsint * hp;
724 f4 = -tet*cos1t;
725 f5 = sint;
726 f6 = tet * cos1t * hp;
727
728 vout[ix] = vect[ix] + f1*vect[ipx] + f2*hxp[0];
729 vout[iy] = vect[iy] + f1*vect[ipy] + f2*hxp[1];
730 vout[iz] = vect[iz] + f1*vect[ipz] + f3;
731
732 vout[ipx] = vect[ipx] + f4*vect[ipx] + f5*hxp[0];
733 vout[ipy] = vect[ipy] + f4*vect[ipy] + f5*hxp[1];
734 vout[ipz] = vect[ipz] + f4*vect[ipz] + f6;
735
736 return;
737}
738 //__________________________________________________________________________
739void AliMUONTrackParam::ExtrapOneStepRungekutta(Double_t charge, Double_t step,
740 Double_t* vect, Double_t* vout)
741{
742//
743// ******************************************************************
744// * *
745// * Runge-Kutta method for tracking a particle through a magnetic *
746// * field. Uses Nystroem algorithm (See Handbook Nat. Bur. of *
747// * Standards, procedure 25.5.20) *
748// * *
749// * Input parameters *
750// * CHARGE Particle charge *
751// * STEP Step size *
752// * VECT Initial co-ords,direction cosines,momentum *
753// * Output parameters *
754// * VOUT Output co-ords,direction cosines,momentum *
755// * User routine called *
756// * CALL GUFLD(X,F) *
757// * *
758// * ==>Called by : <USER>, GUSWIM *
759// * Authors R.Brun, M.Hansroul ********* *
760// * V.Perevoztchikov (CUT STEP implementation) *
761// * *
762// * *
763// ******************************************************************
764//
765
766 Double_t h2, h4, f[4];
767 Double_t xyzt[3], a, b, c, ph,ph2;
768 Double_t secxs[4],secys[4],seczs[4],hxp[3];
769 Double_t g1, g2, g3, g4, g5, g6, ang2, dxt, dyt, dzt;
770 Double_t est, at, bt, ct, cba;
771 Double_t f1, f2, f3, f4, rho, tet, hnorm, hp, rho1, sint, cost;
772
773 Double_t x;
774 Double_t y;
775 Double_t z;
776
777 Double_t xt;
778 Double_t yt;
779 Double_t zt;
780
781 Double_t maxit = 1992;
782 Double_t maxcut = 11;
783
784 const Double_t dlt = 1e-4;
785 const Double_t dlt32 = dlt/32.;
786 const Double_t third = 1./3.;
787 const Double_t half = 0.5;
788 const Double_t ec = 2.9979251e-4;
789
790 const Double_t pisqua = 9.86960440109;
791 const Int_t ix = 0;
792 const Int_t iy = 1;
793 const Int_t iz = 2;
794 const Int_t ipx = 3;
795 const Int_t ipy = 4;
796 const Int_t ipz = 5;
797
798 // *.
799 // *. ------------------------------------------------------------------
800 // *.
801 // * this constant is for units cm,gev/c and kgauss
802 // *
803 Int_t iter = 0;
804 Int_t ncut = 0;
805 for(Int_t j = 0; j < 7; j++)
806 vout[j] = vect[j];
807
808 Double_t pinv = ec * charge / vect[6];
809 Double_t tl = 0.;
810 Double_t h = step;
811 Double_t rest;
812
813
814 do {
815 rest = step - tl;
816 if (TMath::Abs(h) > TMath::Abs(rest)) h = rest;
817 //cmodif: call gufld(vout,f) changed into:
818
819 GetField(vout,f);
820
821 // *
822 // * start of integration
823 // *
824 x = vout[0];
825 y = vout[1];
826 z = vout[2];
827 a = vout[3];
828 b = vout[4];
829 c = vout[5];
830
831 h2 = half * h;
832 h4 = half * h2;
833 ph = pinv * h;
834 ph2 = half * ph;
835 secxs[0] = (b * f[2] - c * f[1]) * ph2;
836 secys[0] = (c * f[0] - a * f[2]) * ph2;
837 seczs[0] = (a * f[1] - b * f[0]) * ph2;
838 ang2 = (secxs[0]*secxs[0] + secys[0]*secys[0] + seczs[0]*seczs[0]);
839 if (ang2 > pisqua) break;
840
841 dxt = h2 * a + h4 * secxs[0];
842 dyt = h2 * b + h4 * secys[0];
843 dzt = h2 * c + h4 * seczs[0];
844 xt = x + dxt;
845 yt = y + dyt;
846 zt = z + dzt;
847 // *
848 // * second intermediate point
849 // *
850
851 est = TMath::Abs(dxt) + TMath::Abs(dyt) + TMath::Abs(dzt);
852 if (est > h) {
853 if (ncut++ > maxcut) break;
854 h *= half;
855 continue;
856 }
857
858 xyzt[0] = xt;
859 xyzt[1] = yt;
860 xyzt[2] = zt;
861
862 //cmodif: call gufld(xyzt,f) changed into:
863 GetField(xyzt,f);
864
865 at = a + secxs[0];
866 bt = b + secys[0];
867 ct = c + seczs[0];
868
869 secxs[1] = (bt * f[2] - ct * f[1]) * ph2;
870 secys[1] = (ct * f[0] - at * f[2]) * ph2;
871 seczs[1] = (at * f[1] - bt * f[0]) * ph2;
872 at = a + secxs[1];
873 bt = b + secys[1];
874 ct = c + seczs[1];
875 secxs[2] = (bt * f[2] - ct * f[1]) * ph2;
876 secys[2] = (ct * f[0] - at * f[2]) * ph2;
877 seczs[2] = (at * f[1] - bt * f[0]) * ph2;
878 dxt = h * (a + secxs[2]);
879 dyt = h * (b + secys[2]);
880 dzt = h * (c + seczs[2]);
881 xt = x + dxt;
882 yt = y + dyt;
883 zt = z + dzt;
884 at = a + 2.*secxs[2];
885 bt = b + 2.*secys[2];
886 ct = c + 2.*seczs[2];
887
888 est = TMath::Abs(dxt)+TMath::Abs(dyt)+TMath::Abs(dzt);
889 if (est > 2.*TMath::Abs(h)) {
890 if (ncut++ > maxcut) break;
891 h *= half;
892 continue;
893 }
894
895 xyzt[0] = xt;
896 xyzt[1] = yt;
897 xyzt[2] = zt;
898
899 //cmodif: call gufld(xyzt,f) changed into:
900 GetField(xyzt,f);
901
902 z = z + (c + (seczs[0] + seczs[1] + seczs[2]) * third) * h;
903 y = y + (b + (secys[0] + secys[1] + secys[2]) * third) * h;
904 x = x + (a + (secxs[0] + secxs[1] + secxs[2]) * third) * h;
905
906 secxs[3] = (bt*f[2] - ct*f[1])* ph2;
907 secys[3] = (ct*f[0] - at*f[2])* ph2;
908 seczs[3] = (at*f[1] - bt*f[0])* ph2;
909 a = a+(secxs[0]+secxs[3]+2. * (secxs[1]+secxs[2])) * third;
910 b = b+(secys[0]+secys[3]+2. * (secys[1]+secys[2])) * third;
911 c = c+(seczs[0]+seczs[3]+2. * (seczs[1]+seczs[2])) * third;
912
913 est = TMath::Abs(secxs[0]+secxs[3] - (secxs[1]+secxs[2]))
914 + TMath::Abs(secys[0]+secys[3] - (secys[1]+secys[2]))
915 + TMath::Abs(seczs[0]+seczs[3] - (seczs[1]+seczs[2]));
916
917 if (est > dlt && TMath::Abs(h) > 1.e-4) {
918 if (ncut++ > maxcut) break;
919 h *= half;
920 continue;
921 }
922
923 ncut = 0;
924 // * if too many iterations, go to helix
925 if (iter++ > maxit) break;
926
927 tl += h;
928 if (est < dlt32)
929 h *= 2.;
930 cba = 1./ TMath::Sqrt(a*a + b*b + c*c);
931 vout[0] = x;
932 vout[1] = y;
933 vout[2] = z;
934 vout[3] = cba*a;
935 vout[4] = cba*b;
936 vout[5] = cba*c;
937 rest = step - tl;
938 if (step < 0.) rest = -rest;
939 if (rest < 1.e-5*TMath::Abs(step)) return;
940
941 } while(1);
942
943 // angle too big, use helix
944
945 f1 = f[0];
946 f2 = f[1];
947 f3 = f[2];
948 f4 = TMath::Sqrt(f1*f1+f2*f2+f3*f3);
949 rho = -f4*pinv;
950 tet = rho * step;
951
952 hnorm = 1./f4;
953 f1 = f1*hnorm;
954 f2 = f2*hnorm;
955 f3 = f3*hnorm;
956
957 hxp[0] = f2*vect[ipz] - f3*vect[ipy];
958 hxp[1] = f3*vect[ipx] - f1*vect[ipz];
959 hxp[2] = f1*vect[ipy] - f2*vect[ipx];
960
961 hp = f1*vect[ipx] + f2*vect[ipy] + f3*vect[ipz];
962
963 rho1 = 1./rho;
964 sint = TMath::Sin(tet);
965 cost = 2.*TMath::Sin(half*tet)*TMath::Sin(half*tet);
966
967 g1 = sint*rho1;
968 g2 = cost*rho1;
969 g3 = (tet-sint) * hp*rho1;
970 g4 = -cost;
971 g5 = sint;
972 g6 = cost * hp;
973
974 vout[ix] = vect[ix] + g1*vect[ipx] + g2*hxp[0] + g3*f1;
975 vout[iy] = vect[iy] + g1*vect[ipy] + g2*hxp[1] + g3*f2;
976 vout[iz] = vect[iz] + g1*vect[ipz] + g2*hxp[2] + g3*f3;
977
978 vout[ipx] = vect[ipx] + g4*vect[ipx] + g5*hxp[0] + g6*f1;
979 vout[ipy] = vect[ipy] + g4*vect[ipy] + g5*hxp[1] + g6*f2;
980 vout[ipz] = vect[ipz] + g4*vect[ipz] + g5*hxp[2] + g6*f3;
981
982 return;
983}
984//___________________________________________________________
985 void AliMUONTrackParam::GetField(Double_t *Position, Double_t *Field)
986{
987 // interface to "gAlice->Field()->Field" for arguments in double precision
988
989 Float_t x[3], b[3];
990
991 x[0] = Position[0]; x[1] = Position[1]; x[2] = Position[2];
992
993 gAlice->Field()->Field(x, b);
994 Field[0] = b[0]; Field[1] = b[1]; Field[2] = b[2];
995
996 return;
997 }