76de088626eb87056252805f8bd839018133825d
[u/mrichter/AliRoot.git] / HMPID / AliHMPIDRecon.cxx
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15
16 //////////////////////////////////////////////////////////////////////////
17 //                                                                      //
18 // AliHMPIDRecon                                                         //
19 //                                                                      //
20 // HMPID class to perfom pattern recognition based on Hough transfrom    //
21 // for single chamber                                                   //
22 //////////////////////////////////////////////////////////////////////////
23
24 #include "AliHMPIDRecon.h"   //class header
25 #include "AliHMPIDCluster.h" //CkovAngle()
26 #include <TRotation.h>       //TracePhot()
27 #include <TH1D.h>            //HoughResponse()
28 #include <TClonesArray.h>    //CkovAngle()
29 #include <AliESDtrack.h>     //CkovAngle()
30
31 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
32 AliHMPIDRecon::AliHMPIDRecon():
33   TTask("RichRec","RichPat"),
34   fPhotCnt(-1),
35   fPhotFlag(0x0),
36   fPhotCkov(0x0),
37   fPhotPhi(0x0),
38   fPhotWei(0x0),
39   fCkovSigma2(0),
40   fIsWEIGHT(kFALSE),
41   fDTheta(0.001),
42   fWindowWidth(0.045),
43   fRingArea(0),
44   fRingAcc(0),
45   fTrkDir(0,0,1),  // Just for test
46   fTrkPos(30,40),  // Just for test
47   fMipPos(0,0),
48   fPc(0,0),
49   fParam(AliHMPIDParam::Instance())
50 {
51 //..
52 //init of data members
53 //..
54   
55   fParam->SetRefIdx(fParam->MeanIdxRad()); // initialization of ref index to a default one
56 }
57 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
58 void AliHMPIDRecon::InitVars(Int_t n)
59 {
60 //..
61 //Init some variables
62 //..
63   if(n<0) return;
64   fPhotFlag = new Int_t[n];
65   fPhotCkov = new Double_t[n];
66   fPhotPhi  = new Double_t[n];
67   fPhotWei  = new Double_t[n];
68 //
69 }
70 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
71 void AliHMPIDRecon::DeleteVars()const
72 {
73 //..
74 //Delete variables
75 //..
76   delete fPhotFlag;
77   delete fPhotCkov;
78   delete fPhotPhi;
79   delete fPhotWei;
80 }
81 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
82 void AliHMPIDRecon::CkovAngle(AliESDtrack *pTrk,TClonesArray *pCluLst,Double_t nmean,Double_t qthre)
83 {
84 // Pattern recognition method based on Hough transform
85 // Arguments:   pTrk     - track for which Ckov angle is to be found
86 //              pCluLst  - list of clusters for this chamber   
87 //   Returns:            - track ckov angle, [rad], 
88     
89
90   const Int_t nMinPhotAcc = 3;                      // Minimum number of photons required to perform the pattern recognition
91   
92   
93   Int_t nClusTot = pCluLst->GetEntries();
94   if(nClusTot>fParam->MultCut()) fIsWEIGHT = kTRUE; // offset to take into account bkg in reconstruction
95   else                           fIsWEIGHT = kFALSE;
96
97   InitVars(nClusTot);
98   
99   Float_t xRa,yRa,th,ph;
100   pTrk->GetHMPIDtrk(xRa,yRa,th,ph);        //initialize this track: th and ph angles at middle of RAD 
101   SetTrack(xRa,yRa,th,ph);
102
103   fParam->SetRefIdx(nmean);
104
105   Float_t dMin=999,mipX=-1,mipY=-1;Int_t chId=-1,mipId=-1,mipQ=-1;
106   Int_t sizeClu = -1;
107   fPhotCnt=0;
108   for (Int_t iClu=0; iClu<pCluLst->GetEntriesFast();iClu++){//clusters loop
109     AliHMPIDCluster *pClu=(AliHMPIDCluster*)pCluLst->UncheckedAt(iClu);                       //get pointer to current cluster    
110     chId=pClu->Ch();
111     if(pClu->Q()>qthre){                                                                      //charge compartible with MIP clusters      
112       Float_t dX=fPc.X()-pClu->X(),dY=fPc.Y()-pClu->Y(),d =TMath::Sqrt(dX*dX+dY*dY);          //distance between current cluster and intersection point
113       if( d < dMin) {mipId=iClu; dMin=d;mipX=pClu->X();
114                      mipY=pClu->Y();mipQ=(Int_t)pClu->Q();sizeClu=pClu->Size();}              //current cluster is closer, overwrite data for min cluster
115     }else{                                                                                    //charge compatible with photon cluster
116       Double_t thetaCer,phiCer;
117       if(FindPhotCkov(pClu->X(),pClu->Y(),thetaCer,phiCer)){                                  //find ckov angle for this  photon candidate
118         fPhotCkov[fPhotCnt]=thetaCer;                                                         //actual theta Cerenkov (in TRS)
119         fPhotPhi [fPhotCnt]=phiCer;                                                           //actual phi   Cerenkov (in TRS): -pi to come back to "unusual" ref system (X,Y,-Z)
120         //PH        Printf("photon n. %i reconstructed theta = %f",fPhotCnt,fPhotCkov[fPhotCnt]);
121         fPhotCnt++;                                                                           //increment counter of photon candidates
122       }
123     }
124   }//clusters loop
125
126   pTrk->SetHMPIDmip(mipX,mipY,mipQ,fPhotCnt);                                                //store mip info in any case 
127   
128   if(nmean < 0){                                                                             //track didn' t pass through the radiator
129     pTrk->SetHMPIDsignal(kNoRad);                                                            //set the appropriate flag
130     pTrk->SetHMPIDcluIdx(chId,mipId+1000*sizeClu);                                           //set index of cluster
131     return;
132   }
133    
134   if(fPhotCnt<=nMinPhotAcc) {                                                                 //no reconstruction with <=3 photon candidates
135     pTrk->SetHMPIDsignal(kNoPhotAccept);                                                      //set the appropriate flag
136     pTrk->SetHMPIDcluIdx(chId,mipId+1000*sizeClu);                                            //set index of cluster
137     return;
138   }
139   
140   if(mipId==-1) {
141     pTrk->SetHMPIDcluIdx(chId,9999);                                                          //set index of cluster
142     pTrk->SetHMPIDsignal(kMipQdcCut);
143     return;
144   }                                                                                           //no clusters with QDC more the threshold at all
145     pTrk->SetHMPIDcluIdx(chId,mipId+1000*sizeClu);                                            //set chamber, index of cluster + cluster size
146     if(dMin>fParam->DistCut()) {pTrk->SetHMPIDsignal(kMipDistCut); return;}                   //closest cluster with enough charge is still too far from intersection
147   
148   fMipPos.Set(mipX,mipY);
149   
150   
151 //PATTERN RECOGNITION STARTED: 
152   
153   Int_t iNrec=FlagPhot(HoughResponse());                                                      //flag photons according to individual theta ckov with respect to most probable
154   pTrk->SetHMPIDmip(mipX,mipY,mipQ,iNrec);                                                    //store mip info 
155
156   if(iNrec<1){
157     pTrk->SetHMPIDsignal(kNoPhotAccept);                                                      //no photon candidates are accepted
158     return;
159   }
160   Double_t thetaC = FindRingCkov(pCluLst->GetEntries());                                    //find the best reconstructed theta Cherenkov
161 //    FindRingGeom(thetaC,2);
162   pTrk->SetHMPIDsignal(thetaC);                                                             //store theta Cherenkov
163   pTrk->SetHMPIDchi2(fCkovSigma2);                                                          //store errors squared
164
165   DeleteVars();
166 }//CkovAngle()
167 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
168 Bool_t AliHMPIDRecon::FindPhotCkov(Double_t cluX,Double_t cluY,Double_t &thetaCer,Double_t &phiCer)
169 {
170 // Finds Cerenkov angle  for this photon candidate
171 // Arguments: cluX,cluY - position of cadidate's cluster  
172 // Returns: Cerenkov angle 
173
174   TVector3 dirCkov;
175   
176   Double_t zRad= -0.5*fParam->RadThick()-0.5*fParam->WinThick();     //z position of middle of RAD
177   TVector3 rad(fTrkPos.X(),fTrkPos.Y(),zRad);                        //impact point at middle of RAD
178   TVector3  pc(cluX,cluY,0.5*fParam->WinThick()+fParam->GapIdx());   //mip at PC
179   Double_t cluR = TMath::Sqrt((cluX-fTrkPos.X())*(cluX-fTrkPos.X())+
180                               (cluY-fTrkPos.Y())*(cluY-fTrkPos.Y()));//ref. distance impact RAD-CLUSTER   
181   Double_t phi=(pc-rad).Phi();                                       //phi of photon
182     
183   Double_t ckov1=0;
184   Double_t ckov2=0.75+fTrkDir.Theta();                        //start to find theta cerenkov in DRS
185   const Double_t kTol=0.01;
186   Int_t iIterCnt = 0;
187   while(1){
188     if(iIterCnt>=50) return kFALSE;
189     Double_t ckov=0.5*(ckov1+ckov2);
190     dirCkov.SetMagThetaPhi(1,ckov,phi);
191     TVector2 posC=TraceForward(dirCkov);                      //trace photon with actual angles
192     Double_t dist=cluR-(posC-fTrkPos).Mod();                  //get distance between trial point and cluster position
193     if(posC.X()==-999) dist = - 999;                          //total reflection problem
194     iIterCnt++;                                               //counter step
195     if     (dist> kTol) ckov1=ckov;                           //cluster @ larger ckov
196     else if(dist<-kTol) ckov2=ckov;                           //cluster @ smaller ckov
197     else{                                                     //precision achived: ckov in DRS found
198       dirCkov.SetMagThetaPhi(1,ckov,phi);                     //
199       Lors2Trs(dirCkov,thetaCer,phiCer);                       //find ckov (in TRS:the effective Cherenkov angle!)
200       return kTRUE;
201     }
202   }
203 }//FindPhotTheta()
204 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
205 TVector2 AliHMPIDRecon::TraceForward(TVector3 dirCkov)const
206 {
207   //Trace forward a photon from (x,y) up to PC
208   // Arguments: dirCkov photon vector in LORS
209   //   Returns: pos of traced photon at PC
210   
211   TVector2 pos(-999,-999);
212   Double_t thetaCer = dirCkov.Theta();
213   if(thetaCer > TMath::ASin(1./fParam->GetRefIdx())) return pos;          //total refraction on WIN-GAP boundary
214   Double_t zRad= -0.5*fParam->RadThick()-0.5*fParam->WinThick();          //z position of middle of RAD
215   TVector3  posCkov(fTrkPos.X(),fTrkPos.Y(),zRad);                        //RAD: photon position is track position @ middle of RAD 
216   Propagate(dirCkov,posCkov,           -0.5*fParam->WinThick());          //go to RAD-WIN boundary  
217   Refract  (dirCkov,         fParam->GetRefIdx(),fParam->WinIdx());       //RAD-WIN refraction
218   Propagate(dirCkov,posCkov,            0.5*fParam->WinThick());          //go to WIN-GAP boundary
219   Refract  (dirCkov,         fParam->WinIdx(),fParam->GapIdx());          //WIN-GAP refraction
220   Propagate(dirCkov,posCkov,0.5*fParam->WinThick()+fParam->GapThick());   //go to PC
221   pos.Set(posCkov.X(),posCkov.Y());
222   return pos;
223 }//TraceForward()
224 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
225 void AliHMPIDRecon::Lors2Trs(TVector3 dirCkov,Double_t &thetaCer,Double_t &phiCer)const
226 {
227   //Theta Cerenkov reconstruction 
228   // Arguments: dirCkov photon vector in LORS
229   //   Returns: thetaCer of photon in TRS
230   //              phiCer of photon in TRS
231 //  TVector3 dirTrk;
232 //  dirTrk.SetMagThetaPhi(1,fTrkDir.Theta(),fTrkDir.Phi());
233 //  Double_t thetaCer = TMath::ACos(dirCkov*dirTrk);
234   TRotation mtheta;   mtheta.RotateY(-fTrkDir.Theta());
235   TRotation mphi;       mphi.RotateZ(-fTrkDir.Phi());
236   TRotation mrot=mtheta*mphi;
237   TVector3 dirCkovTRS;
238   dirCkovTRS=mrot*dirCkov;
239   phiCer  = dirCkovTRS.Phi();                                          //actual value of the phi of the photon
240   thetaCer= dirCkovTRS.Theta();                                        //actual value of thetaCerenkov of the photon
241 }
242 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
243 void AliHMPIDRecon::Trs2Lors(TVector3 dirCkov,Double_t &thetaCer,Double_t &phiCer)const
244 {
245   //Theta Cerenkov reconstruction 
246   // Arguments: dirCkov photon vector in TRS
247   //   Returns: thetaCer of photon in LORS
248   //              phiCer of photon in LORS
249   TRotation mtheta;   mtheta.RotateY(fTrkDir.Theta());
250   TRotation mphi;       mphi.RotateZ(fTrkDir.Phi());
251   TRotation mrot=mphi*mtheta;
252   TVector3 dirCkovLORS;
253   dirCkovLORS=mrot*dirCkov;
254   phiCer  = dirCkovLORS.Phi();                                          //actual value of the phi of the photon
255   thetaCer= dirCkovLORS.Theta();                                        //actual value of thetaCerenkov of the photon
256 }
257 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
258 void AliHMPIDRecon::FindRingGeom(Double_t ckovAng,Int_t level)
259 {
260 // Find area covered in the PC acceptance
261 // Arguments: ckovAng - cerenkov angle
262 //            level   - precision in finding area and portion of ring accepted (multiple of 50)
263 //   Returns: area of the ring in cm^2 for given theta ckov
264    
265   Int_t kN=50*level;
266   Int_t nPoints = 0;
267   Double_t area=0;
268   
269   Bool_t first=kFALSE;
270   TVector2 pos1;
271   
272   for(Int_t i=0;i<kN;i++){
273    if(!first) {
274       pos1=TracePhot(ckovAng,Double_t(TMath::TwoPi()*(i+1)/kN));                                    //find a good trace for the first photon
275      if(pos1.X()==-999) continue;                                                                   //no area: open ring                  
276      if(!fParam->IsInside(pos1.X(),pos1.Y(),0)) {
277        pos1 = IntWithEdge(fMipPos,pos1);                                                            // find the very first intersection...
278      } else {
279        if(!AliHMPIDParam::IsInDead(pos1.X(),pos1.Y())) nPoints++;                                   //photon is accepted if not in dead zone
280      }
281      first=kTRUE;
282      continue;
283    }
284    TVector2 pos2=TracePhot(ckovAng,Double_t(TMath::TwoPi()*(i+1)/kN));                              //trace the next photon
285    if(pos2.X()==-999) continue;                                                                     //no area: open ring             
286    if(!fParam->IsInside(pos2.X(),pos2.Y(),0)) {
287      pos2 = IntWithEdge(fMipPos,pos2);
288    } else {
289      if(!AliHMPIDParam::IsInDead(pos2.X(),pos2.Y())) nPoints++;                                     //photon is accepted if not in dead zone
290    }
291    area+=TMath::Abs((pos1-fMipPos).X()*(pos2-fMipPos).Y()-(pos1-fMipPos).Y()*(pos2-fMipPos).X());   //add area of the triangle...            
292    pos1 = pos2;
293   }
294 //---  find area and length of the ring;
295   fRingAcc = (Double_t)nPoints/(Double_t)kN;
296   area*=0.5;
297   fRingArea = area;
298 }//FindRingGeom()
299 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
300 TVector2 AliHMPIDRecon::IntWithEdge(TVector2 p1,TVector2 p2)const
301 {
302 // It finds the intersection of the line for 2 points traced as photons
303 // and the edge of a given PC
304 // Arguments: 2 points obtained tracing the photons
305 //   Returns: intersection point with detector (PC) edges
306
307   Double_t xmin = (p1.X()<p2.X())? p1.X():p2.X(); 
308   Double_t xmax = (p1.X()<p2.X())? p2.X():p1.X(); 
309   Double_t ymin = (p1.Y()<p2.Y())? p1.Y():p2.Y(); 
310   Double_t ymax = (p1.Y()<p2.Y())? p2.Y():p1.Y(); 
311   
312   Double_t m = TMath::Tan((p2-p1).Phi());
313   TVector2 pint;
314   //intersection with low  X
315   pint.Set((Double_t)(p1.X() + (0-p1.Y())/m),0.);
316   if(pint.X()>=0 && pint.X()<=fParam->SizeAllX() &&
317      pint.X()>=xmin && pint.X()<=xmax            &&
318      pint.Y()>=ymin && pint.Y()<=ymax) return pint;
319   //intersection with high X  
320   pint.Set((Double_t)(p1.X() + (fParam->SizeAllY()-p1.Y())/m),(Double_t)(fParam->SizeAllY()));
321   if(pint.X()>=0 && pint.X()<=fParam->SizeAllX() &&
322      pint.X()>=xmin && pint.X()<=xmax            &&
323      pint.Y()>=ymin && pint.Y()<=ymax) return pint;
324   //intersection with left Y  
325   pint.Set(0.,(Double_t)(p1.Y() + m*(0-p1.X())));
326   if(pint.Y()>=0 && pint.Y()<=fParam->SizeAllY() &&
327      pint.Y()>=ymin && pint.Y()<=ymax            &&
328      pint.X()>=xmin && pint.X()<=xmax) return pint;
329   //intersection with righ Y  
330   pint.Set((Double_t)(fParam->SizeAllX()),(Double_t)(p1.Y() + m*(fParam->SizeAllX()-p1.X())));
331   if(pint.Y()>=0 && pint.Y()<=fParam->SizeAllY() &&
332      pint.Y()>=ymin && pint.Y()<=ymax            &&
333      pint.X()>=xmin && pint.X()<=xmax) return pint;
334   return p1;
335 }//IntWithEdge()
336 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
337 Double_t AliHMPIDRecon::FindRingCkov(Int_t)
338 {
339 // Loops on all Ckov candidates and estimates the best Theta Ckov for a ring formed by those candidates. Also estimates an error for that Theat Ckov
340 // collecting errors for all single Ckov candidates thetas. (Assuming they are independent)  
341 // Arguments: iNclus- total number of clusters in chamber for background estimation
342 //    Return: best estimation of track Theta ckov
343
344   Double_t wei = 0.;
345   Double_t weightThetaCerenkov = 0.;
346
347   Double_t ckovMin=9999.,ckovMax=0.;
348   Double_t sigma2 = 0;   //to collect error squared for this ring
349   
350   for(Int_t i=0;i<fPhotCnt;i++){//candidates loop
351     if(fPhotFlag[i] == 2){
352       if(fPhotCkov[i]<ckovMin) ckovMin=fPhotCkov[i];                         //find max and min Theta ckov from all candidates within probable window
353       if(fPhotCkov[i]>ckovMax) ckovMax=fPhotCkov[i]; 
354       weightThetaCerenkov += fPhotCkov[i]*fPhotWei[i];
355       wei += fPhotWei[i];                                                    //collect weight as sum of all candidate weghts   
356       
357       sigma2 += 1./fParam->Sigma2(fTrkDir.Theta(),fTrkDir.Phi(),fPhotCkov[i],fPhotPhi[i]);
358     }
359   }//candidates loop
360   
361   if(sigma2>0) fCkovSigma2=1./sigma2;
362   else         fCkovSigma2=1e10;  
363   
364   if(wei != 0.) weightThetaCerenkov /= wei; else weightThetaCerenkov = 0.;
365   return weightThetaCerenkov;
366 }//FindCkovRing()
367 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
368 Int_t AliHMPIDRecon::FlagPhot(Double_t ckov)
369 {
370 // Flag photon candidates if their individual ckov angle is inside the window around ckov angle returned by  HoughResponse()
371 // Arguments: ckov- value of most probable ckov angle for track as returned by HoughResponse()
372 //   Returns: number of photon candidates happened to be inside the window
373
374 // Photon Flag:  Flag = 0 initial set; 
375 //               Flag = 1 good candidate (charge compatible with photon); 
376 //               Flag = 2 photon used for the ring;
377   
378   Int_t steps = (Int_t)((ckov )/ fDTheta); //how many times we need to have fDTheta to fill the distance between 0  and thetaCkovHough
379
380   Double_t tmin = (Double_t)(steps - 1)*fDTheta;
381   Double_t tmax = (Double_t)(steps)*fDTheta;
382   Double_t tavg = 0.5*(tmin+tmax);
383
384   tmin = tavg - 0.5*fWindowWidth;  tmax = tavg + 0.5*fWindowWidth;
385
386   Int_t iInsideCnt = 0; //count photons which Theta ckov inside the window
387   for(Int_t i=0;i<fPhotCnt;i++){//photon candidates loop
388     fPhotFlag[i] = 0;
389     if(fPhotCkov[i] >= tmin && fPhotCkov[i] <= tmax)    { 
390       fPhotFlag[i]=2;     
391       iInsideCnt++;
392     }
393   }
394   return iInsideCnt;
395 }//FlagPhot()
396 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
397 TVector2 AliHMPIDRecon::TracePhot(Double_t ckovThe,Double_t ckovPhi)const
398 {
399 // Trace a single Ckov photon from emission point somewhere in radiator up to photocathode taking into account ref indexes of materials it travereses
400 // Arguments: ckovThe,ckovPhi- photon ckov angles in TRS, [rad]
401 //   Returns: distance between photon point on PC and track projection  
402   
403   Double_t theta,phi;
404   TVector3  dirTRS,dirLORS;   
405   dirTRS.SetMagThetaPhi(1,ckovThe,ckovPhi);                     //photon in TRS
406   Trs2Lors(dirTRS,theta,phi);
407   dirLORS.SetMagThetaPhi(1,theta,phi);                          //photon in LORS
408   return TraceForward(dirLORS);                                 //now foward tracing
409 }//TracePhot()
410 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
411 void AliHMPIDRecon::Propagate(const TVector3 dir,TVector3 &pos,Double_t z)const
412 {
413 // Finds an intersection point between a line and XY plane shifted along Z.
414 // Arguments:  dir,pos   - vector along the line and any point of the line
415 //             z         - z coordinate of plain 
416 //   Returns:  none
417 //   On exit:  pos is the position if this intesection if any
418   static TVector3 nrm(0,0,1); 
419          TVector3 pnt(0,0,z);
420   
421   TVector3 diff=pnt-pos;
422   Double_t sint=(nrm*diff)/(nrm*dir);
423   pos+=sint*dir;
424 }//Propagate()
425 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
426 void AliHMPIDRecon::Refract(TVector3 &dir,Double_t n1,Double_t n2)const
427 {
428 // Refract direction vector according to Snell law
429 // Arguments: 
430 //            n1 - ref idx of first substance
431 //            n2 - ref idx of second substance
432 //   Returns: none
433 //   On exit: dir is new direction
434   Double_t sinref=(n1/n2)*TMath::Sin(dir.Theta());
435   if(TMath::Abs(sinref)>1.) dir.SetXYZ(-999,-999,-999);
436   else             dir.SetTheta(TMath::ASin(sinref));
437 }//Refract()
438 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
439 Double_t AliHMPIDRecon::HoughResponse()
440 {
441 //
442 //    fIdxMip = mipId;
443
444 //       
445   Double_t kThetaMax=0.75;
446   Int_t nChannels = (Int_t)(kThetaMax/fDTheta+0.5);
447   TH1D *phots   = new TH1D("Rphot"  ,"phots"         ,nChannels,0,kThetaMax);
448   TH1D *photsw  = new TH1D("RphotWeighted" ,"photsw" ,nChannels,0,kThetaMax);
449   TH1D *resultw = new TH1D("resultw","resultw"       ,nChannels,0,kThetaMax);
450   Int_t nBin = (Int_t)(kThetaMax/fDTheta);
451   Int_t nCorrBand = (Int_t)(fWindowWidth/(2*fDTheta));
452   
453   for (Int_t i=0; i< fPhotCnt; i++){//photon cadidates loop
454     Double_t angle = fPhotCkov[i];  if(angle<0||angle>kThetaMax) continue;
455     phots->Fill(angle);
456     Int_t bin = (Int_t)(0.5+angle/(fDTheta));
457     Double_t weight=1.;
458     if(fIsWEIGHT){
459       Double_t lowerlimit = ((Double_t)bin)*fDTheta - 0.5*fDTheta;  Double_t upperlimit = ((Double_t)bin)*fDTheta + 0.5*fDTheta;
460       FindRingGeom(lowerlimit);
461       Double_t areaLow  = GetRingArea();
462       FindRingGeom(upperlimit);
463       Double_t areaHigh = GetRingArea();
464       Double_t diffArea = areaHigh - areaLow;
465       if(diffArea>0) weight = 1./diffArea;
466     }
467     photsw->Fill(angle,weight);
468     fPhotWei[i]=weight;
469   }//photon candidates loop 
470    
471   for (Int_t i=1; i<=nBin;i++){
472     Int_t bin1= i-nCorrBand;
473     Int_t bin2= i+nCorrBand;
474     if(bin1<1) bin1=1;
475     if(bin2>nBin)bin2=nBin;
476     Double_t sumPhots=phots->Integral(bin1,bin2);
477     if(sumPhots<3) continue;                            // if less then 3 photons don't trust to this ring
478     Double_t sumPhotsw=photsw->Integral(bin1,bin2);
479     resultw->Fill((Double_t)((i+0.5)*fDTheta),sumPhotsw);
480   } 
481 // evaluate the "BEST" theta ckov as the maximum value of histogramm
482   Double_t *pVec = resultw->GetArray();
483   Int_t locMax = TMath::LocMax(nBin,pVec);
484   delete phots;delete photsw;delete resultw; // Reset and delete objects
485   
486   return (Double_t)(locMax*fDTheta+0.5*fDTheta); //final most probable track theta ckov   
487 }//HoughResponse()
488 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++