HMPID/AliHMPIDRecon.cxx

   1 /**************************************************************************
   2  * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
   3  *                                                                        *
   4  * Author: The ALICE Off-line Project.                                    *
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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,Int_t index,Double_t nmean,Float_t xRa,Float_t yRa)
  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   Int_t nClusTot = pCluLst->GetEntries();
  93   if(nClusTot>fParam->MultCut()) fIsWEIGHT = kTRUE; // offset to take into account bkg in reconstruction
  94   else                           fIsWEIGHT = kFALSE;
  95
  96   InitVars(nClusTot);
  97
  98   Float_t xPc,yPc,th,ph;
  99   pTrk->GetHMPIDtrk(xPc,yPc,th,ph);        //initialize this track: th and ph angles at middle of RAD
 100   SetTrack(xRa,yRa,th,ph);
 101
 102   fParam->SetRefIdx(nmean);
 103
 104   Float_t mipX=-1,mipY=-1;
 105   Int_t chId=-1,mipQ=-1,sizeClu = -1;
 106
 107   fPhotCnt=0;
 108
 109   for (Int_t iClu=0; iClu<pCluLst->GetEntriesFast();iClu++){//clusters loop
 110     AliHMPIDCluster *pClu=(AliHMPIDCluster*)pCluLst->UncheckedAt(iClu);                       //get pointer to current cluster
 111     if(iClu == index) {                                                                       // this is the MIP! not a photon candidate: just store mip info
 112       mipX = pClu->X();
 113       mipY = pClu->Y();
 114       mipQ=(Int_t)pClu->Q();
 115       sizeClu=pClu->Size();
 116       continue;
 117     }
 118     chId=pClu->Ch();
 119     Double_t thetaCer,phiCer;
 120     if(FindPhotCkov(pClu->X(),pClu->Y(),thetaCer,phiCer)){                                    //find ckov angle for this  photon candidate
 121       fPhotCkov[fPhotCnt]=thetaCer;                                                           //actual theta Cerenkov (in TRS)
 122       fPhotPhi [fPhotCnt]=phiCer;                                                             //actual phi   Cerenkov (in TRS): -pi to come back to "unusual" ref system (X,Y,-Z)
 123       fPhotCnt++;                                                                             //increment counter of photon candidates
 124     }
 125   }//clusters loop
 126
 127   pTrk->SetHMPIDmip(mipX,mipY,mipQ,fPhotCnt);                                                 //store mip info in any case
 128   pTrk->SetHMPIDcluIdx(chId,index+1000*sizeClu);                                              //set index of cluster
 129
 130   if(fPhotCnt<=nMinPhotAcc) {                                                                 //no reconstruction with <=3 photon candidates
 131     pTrk->SetHMPIDsignal(kNoPhotAccept);                                                      //set the appropriate flag
 132     return;
 133   }
 134
 135
 136   fMipPos.Set(mipX,mipY);
 137
 138
 139 //PATTERN RECOGNITION STARTED:
 140
 141   Int_t iNrec=FlagPhot(HoughResponse());                                                      //flag photons according to individual theta ckov with respect to most probable
 142   pTrk->SetHMPIDmip(mipX,mipY,mipQ,iNrec);                                                    //store mip info
 143
 144   if(iNrec<1){
 145     pTrk->SetHMPIDsignal(kNoPhotAccept);                                                      //no photon candidates are accepted
 146     return;
 147   }
 148   Double_t thetaC = FindRingCkov(pCluLst->GetEntries());                                    //find the best reconstructed theta Cherenkov
 149 //    FindRingGeom(thetaC,2);
 150   pTrk->SetHMPIDsignal(thetaC);                                                             //store theta Cherenkov
 151   pTrk->SetHMPIDchi2(fCkovSigma2);                                                          //store errors squared
 152
 153   DeleteVars();
 154 }//CkovAngle()
 155 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 156 Bool_t AliHMPIDRecon::FindPhotCkov(Double_t cluX,Double_t cluY,Double_t &thetaCer,Double_t &phiCer)
 157 {
 158 // Finds Cerenkov angle  for this photon candidate
 159 // Arguments: cluX,cluY - position of cadidate's cluster
 160 // Returns: Cerenkov angle
 161
 162   TVector3 dirCkov;
 163
 164   Double_t zRad= -0.5*fParam->RadThick()-0.5*fParam->WinThick();     //z position of middle of RAD
 165   TVector3 rad(fTrkPos.X(),fTrkPos.Y(),zRad);                        //impact point at middle of RAD
 166   TVector3  pc(cluX,cluY,0.5*fParam->WinThick()+fParam->GapIdx());   //mip at PC
 167   Double_t cluR = TMath::Sqrt((cluX-fTrkPos.X())*(cluX-fTrkPos.X())+
 168                               (cluY-fTrkPos.Y())*(cluY-fTrkPos.Y()));//ref. distance impact RAD-CLUSTER
 169   Double_t phi=(pc-rad).Phi();                                       //phi of photon
 170
 171   Double_t ckov1=0;
 172   Double_t ckov2=0.75+fTrkDir.Theta();                        //start to find theta cerenkov in DRS
 173   const Double_t kTol=0.01;
 174   Int_t iIterCnt = 0;
 175   while(1){
 176     if(iIterCnt>=50) return kFALSE;
 177     Double_t ckov=0.5*(ckov1+ckov2);
 178     dirCkov.SetMagThetaPhi(1,ckov,phi);
 179     TVector2 posC=TraceForward(dirCkov);                      //trace photon with actual angles
 180     Double_t dist=cluR-(posC-fTrkPos).Mod();                  //get distance between trial point and cluster position
 181     if(posC.X()==-999) dist = - 999;                          //total reflection problem
 182     iIterCnt++;                                               //counter step
 183     if     (dist> kTol) ckov1=ckov;                           //cluster @ larger ckov
 184     else if(dist<-kTol) ckov2=ckov;                           //cluster @ smaller ckov
 185     else{                                                     //precision achived: ckov in DRS found
 186       dirCkov.SetMagThetaPhi(1,ckov,phi);                     //
 187       Lors2Trs(dirCkov,thetaCer,phiCer);                       //find ckov (in TRS:the effective Cherenkov angle!)
 188       return kTRUE;
 189     }
 190   }
 191 }//FindPhotTheta()
 192 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 193 TVector2 AliHMPIDRecon::TraceForward(TVector3 dirCkov)const
 194 {
 195   //Trace forward a photon from (x,y) up to PC
 196   // Arguments: dirCkov photon vector in LORS
 197   //   Returns: pos of traced photon at PC
 198
 199   TVector2 pos(-999,-999);
 200   Double_t thetaCer = dirCkov.Theta();
 201   if(thetaCer > TMath::ASin(1./fParam->GetRefIdx())) return pos;          //total refraction on WIN-GAP boundary
 202   Double_t zRad= -0.5*fParam->RadThick()-0.5*fParam->WinThick();          //z position of middle of RAD
 203   TVector3  posCkov(fTrkPos.X(),fTrkPos.Y(),zRad);                        //RAD: photon position is track position @ middle of RAD
 204   Propagate(dirCkov,posCkov,           -0.5*fParam->WinThick());          //go to RAD-WIN boundary
 205   Refract  (dirCkov,         fParam->GetRefIdx(),fParam->WinIdx());       //RAD-WIN refraction
 206   Propagate(dirCkov,posCkov,            0.5*fParam->WinThick());          //go to WIN-GAP boundary
 207   Refract  (dirCkov,         fParam->WinIdx(),fParam->GapIdx());          //WIN-GAP refraction
 208   Propagate(dirCkov,posCkov,0.5*fParam->WinThick()+fParam->GapThick());   //go to PC
 209   pos.Set(posCkov.X(),posCkov.Y());
 210   return pos;
 211 }//TraceForward()
 212 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 213 void AliHMPIDRecon::Lors2Trs(TVector3 dirCkov,Double_t &thetaCer,Double_t &phiCer)const
 214 {
 215   //Theta Cerenkov reconstruction
 216   // Arguments: dirCkov photon vector in LORS
 217   //   Returns: thetaCer of photon in TRS
 218   //              phiCer of photon in TRS
 219 //  TVector3 dirTrk;
 220 //  dirTrk.SetMagThetaPhi(1,fTrkDir.Theta(),fTrkDir.Phi());
 221 //  Double_t thetaCer = TMath::ACos(dirCkov*dirTrk);
 222   TRotation mtheta;   mtheta.RotateY(-fTrkDir.Theta());
 223   TRotation mphi;       mphi.RotateZ(-fTrkDir.Phi());
 224   TRotation mrot=mtheta*mphi;
 225   TVector3 dirCkovTRS;
 226   dirCkovTRS=mrot*dirCkov;
 227   phiCer  = dirCkovTRS.Phi();                                          //actual value of the phi of the photon
 228   thetaCer= dirCkovTRS.Theta();                                        //actual value of thetaCerenkov of the photon
 229 }
 230 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 231 void AliHMPIDRecon::Trs2Lors(TVector3 dirCkov,Double_t &thetaCer,Double_t &phiCer)const
 232 {
 233   //Theta Cerenkov reconstruction
 234   // Arguments: dirCkov photon vector in TRS
 235   //   Returns: thetaCer of photon in LORS
 236   //              phiCer of photon in LORS
 237   TRotation mtheta;   mtheta.RotateY(fTrkDir.Theta());
 238   TRotation mphi;       mphi.RotateZ(fTrkDir.Phi());
 239   TRotation mrot=mphi*mtheta;
 240   TVector3 dirCkovLORS;
 241   dirCkovLORS=mrot*dirCkov;
 242   phiCer  = dirCkovLORS.Phi();                                          //actual value of the phi of the photon
 243   thetaCer= dirCkovLORS.Theta();                                        //actual value of thetaCerenkov of the photon
 244 }
 245 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 246 void AliHMPIDRecon::FindRingGeom(Double_t ckovAng,Int_t level)
 247 {
 248 // Find area covered in the PC acceptance
 249 // Arguments: ckovAng - cerenkov angle
 250 //            level   - precision in finding area and portion of ring accepted (multiple of 50)
 251 //   Returns: area of the ring in cm^2 for given theta ckov
 252
 253   Int_t kN=50*level;
 254   Int_t nPoints = 0;
 255   Double_t area=0;
 256
 257   Bool_t first=kFALSE;
 258   TVector2 pos1;
 259
 260   for(Int_t i=0;i<kN;i++){
 261    if(!first) {
 262       pos1=TracePhot(ckovAng,Double_t(TMath::TwoPi()*(i+1)/kN));                                    //find a good trace for the first photon
 263      if(pos1.X()==-999) continue;                                                                   //no area: open ring
 264      if(!fParam->IsInside(pos1.X(),pos1.Y(),0)) {
 265        pos1 = IntWithEdge(fMipPos,pos1);                                                            // find the very first intersection...
 266      } else {
 267        if(!AliHMPIDParam::IsInDead(pos1.X(),pos1.Y())) nPoints++;                                   //photon is accepted if not in dead zone
 268      }
 269      first=kTRUE;
 270      continue;
 271    }
 272    TVector2 pos2=TracePhot(ckovAng,Double_t(TMath::TwoPi()*(i+1)/kN));                              //trace the next photon
 273    if(pos2.X()==-999) continue;                                                                     //no area: open ring
 274    if(!fParam->IsInside(pos2.X(),pos2.Y(),0)) {
 275      pos2 = IntWithEdge(fMipPos,pos2);
 276    } else {
 277      if(!AliHMPIDParam::IsInDead(pos2.X(),pos2.Y())) nPoints++;                                     //photon is accepted if not in dead zone
 278    }
 279    area+=TMath::Abs((pos1-fMipPos).X()*(pos2-fMipPos).Y()-(pos1-fMipPos).Y()*(pos2-fMipPos).X());   //add area of the triangle...
 280    pos1 = pos2;
 281   }
 282 //---  find area and length of the ring;
 283   fRingAcc = (Double_t)nPoints/(Double_t)kN;
 284   area*=0.5;
 285   fRingArea = area;
 286 }//FindRingGeom()
 287 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 288 TVector2 AliHMPIDRecon::IntWithEdge(TVector2 p1,TVector2 p2)const
 289 {
 290 // It finds the intersection of the line for 2 points traced as photons
 291 // and the edge of a given PC
 292 // Arguments: 2 points obtained tracing the photons
 293 //   Returns: intersection point with detector (PC) edges
 294
 295   Double_t xmin = (p1.X()<p2.X())? p1.X():p2.X();
 296   Double_t xmax = (p1.X()<p2.X())? p2.X():p1.X();
 297   Double_t ymin = (p1.Y()<p2.Y())? p1.Y():p2.Y();
 298   Double_t ymax = (p1.Y()<p2.Y())? p2.Y():p1.Y();
 299
 300   Double_t m = TMath::Tan((p2-p1).Phi());
 301   TVector2 pint;
 302   //intersection with low  X
 303   pint.Set((Double_t)(p1.X() + (0-p1.Y())/m),0.);
 304   if(pint.X()>=0 && pint.X()<=fParam->SizeAllX() &&
 305      pint.X()>=xmin && pint.X()<=xmax            &&
 306      pint.Y()>=ymin && pint.Y()<=ymax) return pint;
 307   //intersection with high X
 308   pint.Set((Double_t)(p1.X() + (fParam->SizeAllY()-p1.Y())/m),(Double_t)(fParam->SizeAllY()));
 309   if(pint.X()>=0 && pint.X()<=fParam->SizeAllX() &&
 310      pint.X()>=xmin && pint.X()<=xmax            &&
 311      pint.Y()>=ymin && pint.Y()<=ymax) return pint;
 312   //intersection with left Y
 313   pint.Set(0.,(Double_t)(p1.Y() + m*(0-p1.X())));
 314   if(pint.Y()>=0 && pint.Y()<=fParam->SizeAllY() &&
 315      pint.Y()>=ymin && pint.Y()<=ymax            &&
 316      pint.X()>=xmin && pint.X()<=xmax) return pint;
 317   //intersection with righ Y
 318   pint.Set((Double_t)(fParam->SizeAllX()),(Double_t)(p1.Y() + m*(fParam->SizeAllX()-p1.X())));
 319   if(pint.Y()>=0 && pint.Y()<=fParam->SizeAllY() &&
 320      pint.Y()>=ymin && pint.Y()<=ymax            &&
 321      pint.X()>=xmin && pint.X()<=xmax) return pint;
 322   return p1;
 323 }//IntWithEdge()
 324 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 325 Double_t AliHMPIDRecon::FindRingCkov(Int_t)
 326 {
 327 // 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
 328 // collecting errors for all single Ckov candidates thetas. (Assuming they are independent)
 329 // Arguments: iNclus- total number of clusters in chamber for background estimation
 330 //    Return: best estimation of track Theta ckov
 331
 332   Double_t wei = 0.;
 333   Double_t weightThetaCerenkov = 0.;
 334
 335   Double_t ckovMin=9999.,ckovMax=0.;
 336   Double_t sigma2 = 0;   //to collect error squared for this ring
 337
 338   for(Int_t i=0;i<fPhotCnt;i++){//candidates loop
 339     if(fPhotFlag[i] == 2){
 340       if(fPhotCkov[i]<ckovMin) ckovMin=fPhotCkov[i];                         //find max and min Theta ckov from all candidates within probable window
 341       if(fPhotCkov[i]>ckovMax) ckovMax=fPhotCkov[i];
 342       weightThetaCerenkov += fPhotCkov[i]*fPhotWei[i];
 343       wei += fPhotWei[i];                                                    //collect weight as sum of all candidate weghts
 344
 345       sigma2 += 1./fParam->Sigma2(fTrkDir.Theta(),fTrkDir.Phi(),fPhotCkov[i],fPhotPhi[i]);
 346     }
 347   }//candidates loop
 348
 349   if(sigma2>0) fCkovSigma2=1./sigma2;
 350   else         fCkovSigma2=1e10;
 351
 352   if(wei != 0.) weightThetaCerenkov /= wei; else weightThetaCerenkov = 0.;
 353   return weightThetaCerenkov;
 354 }//FindCkovRing()
 355 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 356 Int_t AliHMPIDRecon::FlagPhot(Double_t ckov)
 357 {
 358 // Flag photon candidates if their individual ckov angle is inside the window around ckov angle returned by  HoughResponse()
 359 // Arguments: ckov- value of most probable ckov angle for track as returned by HoughResponse()
 360 //   Returns: number of photon candidates happened to be inside the window
 361
 362 // Photon Flag:  Flag = 0 initial set;
 363 //               Flag = 1 good candidate (charge compatible with photon);
 364 //               Flag = 2 photon used for the ring;
 365
 366   Int_t steps = (Int_t)((ckov )/ fDTheta); //how many times we need to have fDTheta to fill the distance between 0  and thetaCkovHough
 367
 368   Double_t tmin = (Double_t)(steps - 1)*fDTheta;
 369   Double_t tmax = (Double_t)(steps)*fDTheta;
 370   Double_t tavg = 0.5*(tmin+tmax);
 371
 372   tmin = tavg - 0.5*fWindowWidth;  tmax = tavg + 0.5*fWindowWidth;
 373
 374   Int_t iInsideCnt = 0; //count photons which Theta ckov inside the window
 375   for(Int_t i=0;i<fPhotCnt;i++){//photon candidates loop
 376     fPhotFlag[i] = 0;
 377     if(fPhotCkov[i] >= tmin && fPhotCkov[i] <= tmax)    {
 378       fPhotFlag[i]=2;
 379       iInsideCnt++;
 380     }
 381   }
 382   return iInsideCnt;
 383 }//FlagPhot()
 384 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 385 TVector2 AliHMPIDRecon::TracePhot(Double_t ckovThe,Double_t ckovPhi)const
 386 {
 387 // Trace a single Ckov photon from emission point somewhere in radiator up to photocathode taking into account ref indexes of materials it travereses
 388 // Arguments: ckovThe,ckovPhi- photon ckov angles in TRS, [rad]
 389 //   Returns: distance between photon point on PC and track projection
 390
 391   Double_t theta,phi;
 392   TVector3  dirTRS,dirLORS;
 393   dirTRS.SetMagThetaPhi(1,ckovThe,ckovPhi);                     //photon in TRS
 394   Trs2Lors(dirTRS,theta,phi);
 395   dirLORS.SetMagThetaPhi(1,theta,phi);                          //photon in LORS
 396   return TraceForward(dirLORS);                                 //now foward tracing
 397 }//TracePhot()
 398 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 399 void AliHMPIDRecon::Propagate(const TVector3 dir,TVector3 &pos,Double_t z)const
 400 {
 401 // Finds an intersection point between a line and XY plane shifted along Z.
 402 // Arguments:  dir,pos   - vector along the line and any point of the line
 403 //             z         - z coordinate of plain
 404 //   Returns:  none
 405 //   On exit:  pos is the position if this intesection if any
 406   static TVector3 nrm(0,0,1);
 407          TVector3 pnt(0,0,z);
 408
 409   TVector3 diff=pnt-pos;
 410   Double_t sint=(nrm*diff)/(nrm*dir);
 411   pos+=sint*dir;
 412 }//Propagate()
 413 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 414 void AliHMPIDRecon::Refract(TVector3 &dir,Double_t n1,Double_t n2)const
 415 {
 416 // Refract direction vector according to Snell law
 417 // Arguments:
 418 //            n1 - ref idx of first substance
 419 //            n2 - ref idx of second substance
 420 //   Returns: none
 421 //   On exit: dir is new direction
 422   Double_t sinref=(n1/n2)*TMath::Sin(dir.Theta());
 423   if(TMath::Abs(sinref)>1.) dir.SetXYZ(-999,-999,-999);
 424   else             dir.SetTheta(TMath::ASin(sinref));
 425 }//Refract()
 426 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 427 Double_t AliHMPIDRecon::HoughResponse()
 428 {
 429 //
 430 //    fIdxMip = mipId;
 431
 432 //
 433   Double_t kThetaMax=0.75;
 434   Int_t nChannels = (Int_t)(kThetaMax/fDTheta+0.5);
 435   TH1D *phots   = new TH1D("Rphot"  ,"phots"         ,nChannels,0,kThetaMax);
 436   TH1D *photsw  = new TH1D("RphotWeighted" ,"photsw" ,nChannels,0,kThetaMax);
 437   TH1D *resultw = new TH1D("resultw","resultw"       ,nChannels,0,kThetaMax);
 438   Int_t nBin = (Int_t)(kThetaMax/fDTheta);
 439   Int_t nCorrBand = (Int_t)(fWindowWidth/(2*fDTheta));
 440
 441   for (Int_t i=0; i< fPhotCnt; i++){//photon cadidates loop
 442     Double_t angle = fPhotCkov[i];  if(angle<0||angle>kThetaMax) continue;
 443     phots->Fill(angle);
 444     Int_t bin = (Int_t)(0.5+angle/(fDTheta));
 445     Double_t weight=1.;
 446     if(fIsWEIGHT){
 447       Double_t lowerlimit = ((Double_t)bin)*fDTheta - 0.5*fDTheta;  Double_t upperlimit = ((Double_t)bin)*fDTheta + 0.5*fDTheta;
 448       FindRingGeom(lowerlimit);
 449       Double_t areaLow  = GetRingArea();
 450       FindRingGeom(upperlimit);
 451       Double_t areaHigh = GetRingArea();
 452       Double_t diffArea = areaHigh - areaLow;
 453       if(diffArea>0) weight = 1./diffArea;
 454     }
 455     photsw->Fill(angle,weight);
 456     fPhotWei[i]=weight;
 457   }//photon candidates loop
 458
 459   for (Int_t i=1; i<=nBin;i++){
 460     Int_t bin1= i-nCorrBand;
 461     Int_t bin2= i+nCorrBand;
 462     if(bin1<1) bin1=1;
 463     if(bin2>nBin)bin2=nBin;
 464     Double_t sumPhots=phots->Integral(bin1,bin2);
 465     if(sumPhots<3) continue;                            // if less then 3 photons don't trust to this ring
 466     Double_t sumPhotsw=photsw->Integral(bin1,bin2);
 467     resultw->Fill((Double_t)((i+0.5)*fDTheta),sumPhotsw);
 468   }
 469 // evaluate the "BEST" theta ckov as the maximum value of histogramm
 470   Double_t *pVec = resultw->GetArray();
 471   Int_t locMax = TMath::LocMax(nBin,pVec);
 472   delete phots;delete photsw;delete resultw; // Reset and delete objects
 473
 474   return (Double_t)(locMax*fDTheta+0.5*fDTheta); //final most probable track theta ckov
 475 }//HoughResponse()
 476 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 477   Double_t AliHMPIDRecon::FindRingExt(Double_t ckov,Int_t ch,Double_t xPc,Double_t yPc,Double_t thRa,Double_t phRa)
 478 {
 479 // To find the acceptance of the ring even from external inputs.
 480 //
 481 //
 482   Double_t xRa = xPc - (fParam->RadThick()+fParam->WinThick()+fParam->GapThick())*TMath::Cos(phRa)*TMath::Tan(thRa); //just linear extrapolation back to RAD
 483   Double_t yRa = yPc - (fParam->RadThick()+fParam->WinThick()+fParam->GapThick())*TMath::Sin(phRa)*TMath::Tan(thRa);
 484
 485   Int_t nStep = 500;
 486   Int_t nPhi = 0;
 487
 488   Int_t ipc,ipadx,ipady;
 489
 490   if(ckov>0){
 491     SetTrack(xRa,yRa,thRa,phRa);
 492     for(Int_t j=0;j<nStep;j++){
 493       TVector2 pos; pos=TracePhot(ckov,j*TMath::TwoPi()/(Double_t)(nStep-1));
 494       if(fParam->IsInDead(pos.X(),pos.Y())) continue;
 495       fParam->Lors2Pad(pos.X(),pos.Y(),ipc,ipadx,ipady);
 496       ipadx+=(ipc%2)*fParam->kPadPcX;
 497       ipady+=(ipc/2)*fParam->kPadPcY;
 498       if(fParam->IsDeadPad(ipadx,ipady,ch)) continue;
 499       nPhi++;
 500     }//point loop
 501   return ((Double_t)nPhi/(Double_t)nStep);
 502   }//if
 503   return -1;
 504 }