VZERO/AliVZERODigitizer.cxx

   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  *                                                                        *
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  10  * copies and that both the copyright notice and this permission notice   *
  11  * appear in the supporting documentation. The authors make no claims     *
  12  * about the suitability of this software for any purpose. It is          *
  13  * provided "as is" without express or implied warranty.                  *
  14  **************************************************************************/
  15
  16 /* $Id$ */
  17
  18 ///_________________________________________________________________________
  19 ///
  20 /// This class constructs Digits out of Hits
  21 ///
  22 ///
  23
  24 // --- Standard library ---
  25
  26 // --- ROOT system ---
  27 #include <TMath.h>
  28 #include <TTree.h>
  29 #include <TMap.h>
  30 #include <TGeoManager.h>
  31 #include <TGeoPhysicalNode.h>
  32 #include <AliGeomManager.h>
  33 #include <TRandom.h>
  34 #include <TF1.h>
  35 #include <TH1F.h>
  36
  37 // --- AliRoot header files ---
  38 #include "AliRun.h"
  39 #include "AliVZERO.h"
  40 #include "AliVZEROhit.h"
  41 #include "AliRunLoader.h"
  42 #include "AliLoader.h"
  43 #include "AliGRPObject.h"
  44 #include "AliRunDigitizer.h"
  45 #include "AliCDBManager.h"
  46 #include "AliCDBStorage.h"
  47 #include "AliCDBEntry.h"
  48 #include "AliVZEROCalibData.h"
  49 #include "AliCTPTimeParams.h"
  50 #include "AliVZEROdigit.h"
  51 #include "AliVZERODigitizer.h"
  52
  53 ClassImp(AliVZERODigitizer)
  54
  55  AliVZERODigitizer::AliVZERODigitizer()
  56                    :AliDigitizer(),
  57                     fCalibData(GetCalibData()),
  58                     fPhotoCathodeEfficiency(0.18),
  59                     fNdigits(0),
  60                     fDigits(0),
  61                     fSignalShape(NULL),
  62                     fPMResponse(NULL),
  63                     fSinglePhESpectrum(NULL)
  64
  65 {
  66   // default constructor
  67
  68 //    fNdigits = 0;
  69 //    fDigits  = 0;
  70 //
  71 //    fPhotoCathodeEfficiency =   0.18;
  72 //    fPMVoltage              =  768.0;
  73 //    fPMGain = TMath::Power((fPMVoltage / 112.5) ,7.04277);
  74
  75 //   fCalibData = GetCalibData();
  76
  77   fSignalShape = new TF1("VZEROSignalShape",this,&AliVZERODigitizer::SignalShape,0,200,6,"AliVZERODigitizer","SignalShape");
  78   //  fSignalShape->SetParameters(0,1.57345e1,-4.25603e-1,2.9,6.40982,3.69339e-01);
  79   fSignalShape->SetParameters(1.34330e+00,1.13007e+02,-4.95705e-01,
  80                               3.68911e+00,1.01040e+00, 3.94675e-01);
  81   fPMResponse = new TF1("VZEROPMResponse",this,&AliVZERODigitizer::PMResponse,-kPMRespTime,2.*kPMRespTime,0,"AliVZERODigitizer","PMResponse");
  82   fSinglePhESpectrum = new TF1("VZEROSinglePhESpectrum",this,&AliVZERODigitizer::SinglePhESpectrum,0,20,0,"AliVZERODigitizer","SinglePhESpectrum");
  83
  84   // Now get the CTP L0->L1 delay
  85   AliCDBEntry *entry = AliCDBManager::Instance()->Get("GRP/CTP/CTPtiming");
  86   if (!entry) AliFatal("CTP timing parameters are not found in OCDB !");
  87   AliCTPTimeParams *ctpParams = (AliCTPTimeParams*)entry->GetObject();
  88   Float_t l1Delay = (Float_t)ctpParams->GetDelayL1L0()*25.0;
  89
  90   AliCDBEntry *entry2 = AliCDBManager::Instance()->Get("VZERO/Calib/TimeDelays");
  91   if (!entry2) AliFatal("VZERO time delays are not found in OCDB !");
  92   TH1F *delays = (TH1F*)entry2->GetObject();
  93
  94   for(Int_t i = 0 ; i < 64; ++i) {
  95
  96     for(Int_t j = 0; j < kNClocks; ++j) fAdc[i][j] = 0;
  97     fLeadingTime[i] = fTimeWidth[i] = 0;
  98
  99     fPmGain[i] = fCalibData->GetGain(i);
 100
 101     fAdcPedestal[i][0] = fCalibData->GetPedestal(i);
 102     fAdcSigma[i][0]    = fCalibData->GetSigma(i);
 103     fAdcPedestal[i][1] = fCalibData->GetPedestal(i+64);
 104     fAdcSigma[i][1]    = fCalibData->GetSigma(i+64);
 105
 106     Int_t board = i / 8;
 107     fNBins[i] = TMath::Nint(((Float_t)(fCalibData->GetMatchWindow(board)+1)*25.0+
 108                              (Float_t)kMaxTDCWidth*fCalibData->GetWidthResolution(board))/
 109                             fCalibData->GetTimeResolution(board));
 110     fNBinsLT[i] = TMath::Nint(((Float_t)(fCalibData->GetMatchWindow(board)+1)*25.0)/
 111                               fCalibData->GetTimeResolution(board));
 112     fBinSize[i] = fCalibData->GetTimeResolution(board);
 113     fHptdcOffset[i] = (((Float_t)fCalibData->GetTriggerCountOffset(board)-
 114                         (Float_t)fCalibData->GetRollOver(board))*25.0+
 115                        fCalibData->GetTimeOffset(i)+
 116                        l1Delay+
 117                        delays->GetBinContent(i+1)+
 118                        kV0Offset);
 119
 120     fTime[i] = new Float_t[fNBins[i]];
 121     memset(fTime[i],0,fNBins[i]*sizeof(Float_t));
 122   }
 123
 124 }
 125
 126 //____________________________________________________________________________
 127   AliVZERODigitizer::AliVZERODigitizer(AliRunDigitizer* manager)
 128                     :AliDigitizer(manager),
 129                      fCalibData(GetCalibData()),
 130                      fPhotoCathodeEfficiency(0.18),
 131                      fNdigits(0),
 132                      fDigits(0),
 133                      fSignalShape(NULL),
 134                      fPMResponse(NULL),
 135                      fSinglePhESpectrum(NULL)
 136
 137 {
 138   // constructor
 139   // Initialize OCDB and containers used in the digitization
 140
 141   fSignalShape = new TF1("VZEROSignalShape",this,&AliVZERODigitizer::SignalShape,0,200,6,"AliVZERODigitizer","SignalShape");
 142   //  fSignalShape->SetParameters(0,1.57345e1,-4.25603e-1,2.9,6.40982,3.69339e-01);
 143   fSignalShape->SetParameters(1.34330e+00,1.13007e+02,-4.95705e-01,
 144                               3.68911e+00,1.01040e+00, 3.94675e-01);
 145   fPMResponse = new TF1("VZEROPMResponse",this,&AliVZERODigitizer::PMResponse,-kPMRespTime,2.*kPMRespTime,0,"AliVZERODigitizer","PMResponse");
 146   fSinglePhESpectrum = new TF1("VZEROSinglePhESpectrum",this,&AliVZERODigitizer::SinglePhESpectrum,0,20,0,"AliVZERODigitizer","SinglePhESpectrum");
 147
 148   // Now get the CTP L0->L1 delay
 149   AliCDBEntry *entry = AliCDBManager::Instance()->Get("GRP/CTP/CTPtiming");
 150   if (!entry) AliFatal("CTP timing parameters are not found in OCDB !");
 151   AliCTPTimeParams *ctpParams = (AliCTPTimeParams*)entry->GetObject();
 152   Float_t l1Delay = (Float_t)ctpParams->GetDelayL1L0()*25.0;
 153
 154   AliCDBEntry *entry2 = AliCDBManager::Instance()->Get("VZERO/Calib/TimeDelays");
 155   if (!entry2) AliFatal("VZERO time delays are not found in OCDB !");
 156   TH1F *delays = (TH1F*)entry2->GetObject();
 157
 158   for(Int_t i = 0 ; i < 64; ++i) {
 159
 160     for(Int_t j = 0; j < kNClocks; ++j) fAdc[i][j] = 0;
 161     fLeadingTime[i] = fTimeWidth[i] = 0;
 162
 163     fPmGain[i] = fCalibData->GetGain(i);
 164
 165     fAdcPedestal[i][0] = fCalibData->GetPedestal(i);
 166     fAdcSigma[i][0]    = fCalibData->GetSigma(i);
 167     fAdcPedestal[i][1] = fCalibData->GetPedestal(i+64);
 168     fAdcSigma[i][1]    = fCalibData->GetSigma(i+64);
 169
 170     Int_t board = i / 8;
 171     fNBins[i] = TMath::Nint(((Float_t)(fCalibData->GetMatchWindow(board)+1)*25.0+
 172                              (Float_t)kMaxTDCWidth*fCalibData->GetWidthResolution(board))/
 173                             fCalibData->GetTimeResolution(board));
 174     fNBinsLT[i] = TMath::Nint(((Float_t)(fCalibData->GetMatchWindow(board)+1)*25.0)/
 175                               fCalibData->GetTimeResolution(board));
 176     fBinSize[i] = fCalibData->GetTimeResolution(board);
 177     fHptdcOffset[i] = (((Float_t)fCalibData->GetTriggerCountOffset(board)-
 178                         (Float_t)fCalibData->GetRollOver(board))*25.0+
 179                        fCalibData->GetTimeOffset(i)+
 180                        l1Delay+
 181                        delays->GetBinContent(i+1)+
 182                        kV0Offset);
 183
 184     fTime[i] = new Float_t[fNBins[i]];
 185     memset(fTime[i],0,fNBins[i]*sizeof(Float_t));
 186   }
 187 }
 188
 189 //____________________________________________________________________________
 190   AliVZERODigitizer::~AliVZERODigitizer()
 191 {
 192   // destructor
 193
 194   if (fDigits) {
 195     fDigits->Delete();
 196     delete fDigits;
 197     fDigits=0;
 198   }
 199
 200   if (fSignalShape) {
 201     delete fSignalShape;
 202     fSignalShape = NULL;
 203   }
 204   if (fPMResponse) {
 205     delete fPMResponse;
 206     fPMResponse = NULL;
 207   }
 208   if (fSinglePhESpectrum) {
 209     delete fSinglePhESpectrum;
 210     fSinglePhESpectrum = NULL;
 211   }
 212
 213   for(Int_t i = 0 ; i < 64; ++i) {
 214     if (fTime[i]) delete [] fTime[i];
 215   }
 216 }
 217
 218 //_____________________________________________________________________________
 219 Bool_t AliVZERODigitizer::Init()
 220 {
 221   // Initialises the digitizer
 222
 223   // Initialises the Digit array
 224   fDigits = new TClonesArray ("AliVZEROdigit", 1000);
 225
 226   return kTRUE;
 227 }
 228
 229 //____________________________________________________________________________
 230 void AliVZERODigitizer::Exec(Option_t* /*option*/)
 231 {
 232   // Creates digits from hits
 233   fNdigits     =    0;
 234
 235   for(Int_t i = 0 ; i < 64; ++i) {
 236     memset(fTime[i],0,fNBins[i]*sizeof(Float_t));
 237     for(Int_t j = 0; j < kNClocks; ++j) fAdc[i][j] = 0;
 238     fLeadingTime[i] = fTimeWidth[i] = 0;
 239   }
 240   Float_t integral = fPMResponse->Integral(-kPMRespTime,2.*kPMRespTime);
 241   Float_t meansPhE = fSinglePhESpectrum->Mean(0,20);
 242
 243   AliRunLoader* outRunLoader =  AliRunLoader::GetRunLoader(fManager->GetOutputFolderName());
 244   if (!outRunLoader) {
 245     Error("Exec", "Can not get output Run Loader");
 246     return;
 247   }
 248
 249   AliLoader* outLoader = outRunLoader->GetLoader("VZEROLoader");
 250
 251   if (!outLoader) {
 252     Error("Exec", "Can not get output VZERO Loader");
 253     return;
 254   }
 255
 256   const char* mode = "update";
 257   if(outRunLoader->GetEventNumber() == 0) mode = "recreate";
 258   outLoader->LoadDigits(mode);
 259
 260   if (!outLoader->TreeD()) outLoader->MakeTree("D");
 261   outLoader->MakeDigitsContainer();
 262   TTree* treeD  = outLoader->TreeD();
 263   Int_t bufsize = 16000;
 264   treeD->Branch("VZERODigit", &fDigits, bufsize);
 265
 266   for (Int_t iInput = 0; iInput < fManager->GetNinputs(); iInput++) {
 267      AliRunLoader* runLoader = AliRunLoader::GetRunLoader(fManager->GetInputFolderName(iInput));
 268      AliLoader* loader = runLoader->GetLoader("VZEROLoader");
 269      if (!loader) {
 270        Error("Exec", "Can not get VZERO Loader for input %d", iInput);
 271        continue;
 272          }
 273
 274      if (!runLoader->GetAliRun()) runLoader->LoadgAlice();
 275
 276      AliVZERO* vzero = (AliVZERO*) runLoader->GetAliRun()->GetDetector("VZERO");
 277      if (!vzero) {
 278        Error("Exec", "No VZERO detector for input %d", iInput);
 279        continue;
 280          }
 281
 282      loader->LoadHits();
 283      TTree* treeH = loader->TreeH();
 284      if (!treeH) {
 285        Error("Exec", "Cannot get TreeH for input %d", iInput);
 286        continue;
 287          }
 288
 289      TClonesArray* hits = vzero->Hits();
 290
 291      //     Float_t lightYieldCorr[64] = {0.00707,0.00517,0.00520,0.00537,0.00735,0.00537,0.00733,0.00605,0.00778,0.00749,0.00701,0.00755,0.00732,0.00617,0.00669,0.00525,0.00752,0.00820,0.00797,0.01107,0.01080,0.00889,0.00880,0.01712,0.00866,0.00701,0.00811,0.00602,0.00879,0.00821,0.00861,0.01433,0.00061,0.00032,0.00099,0.00061,0.00034,0.00046,0.00031,0.00122,0.00155,0.00091,0.00032,0.00096,0.00120,0.00067,0.00113,0.00060,0.00158,0.00136,0.00340,0.00066,0.00076,0.00119,0.00129,0.00147,0.00137,0.00117,0.00088,0.00164,0.00128,0.00081,0.00121,0.00250};
 292      Float_t lightYieldCorr[64] = {0.01173,0.00874,0.00878,0.00886,0.01151,0.00925,0.01167,0.00983,0.01181,0.01243,0.01115,0.01220,0.01228,0.01053,0.01021,0.00930,0.01270,0.01411,0.01316,0.01894,0.01923,0.01860,0.01738,0.00305,0.01584,0.01251,0.01344,0.00310,0.01302,0.01266,0.01407,0.00338,0.00089,0.00100,0.00130,0.00081,0.00052,0.01230,0.00059,0.02452,0.02980,0.00137,0.01421,0.00116,0.00141,0.00092,0.02480,0.00096,0.00182,0.00174,0.00218,0.00106,0.00116,0.00160,0.00162,0.03097,0.00194,0.00171,0.00132,0.00239,0.00173,0.00118,0.00163,0.00262};
 293 //  Now makes Digits from hits
 294      Int_t nTracks = (Int_t) treeH->GetEntries();
 295      for (Int_t iTrack = 0; iTrack < nTracks; iTrack++) {
 296          vzero->ResetHits();
 297          treeH->GetEvent(iTrack);
 298          Int_t nHits = hits->GetEntriesFast();
 299          for (Int_t iHit = 0; iHit < nHits; iHit++) {
 300            AliVZEROhit* hit = (AliVZEROhit *)hits->UncheckedAt(iHit);
 301            Int_t nPhot = hit->Nphot();
 302            Int_t cell  = hit->Cell();
 303            Int_t pmt = Cell2Pmt(cell);
 304            Float_t dt_scintillator = gRandom->Gaus(0,kIntTimeRes);
 305            Float_t t = dt_scintillator + 1e9*hit->Tof();
 306            if (pmt < 32) t += kV0CDelayCables;
 307            t += fHptdcOffset[pmt];
 308            Int_t nPhE;
 309            Float_t prob = lightYieldCorr[pmt]*fPhotoCathodeEfficiency; // Optical losses included!
 310            if (nPhot > 100)
 311              nPhE =gRandom->Gaus(prob*Float_t(nPhot)+0.5,
 312                                  sqrt(Float_t(nPhot)*prob*(1.-prob)));
 313            else
 314              nPhE = gRandom->Binomial(nPhot,prob);
 315            Float_t charge = TMath::Qe()*fPmGain[pmt]*fBinSize[pmt]/integral;
 316            for (Int_t iPhE = 0; iPhE < nPhE; ++iPhE) {
 317              Float_t tPhE = t + fSignalShape->GetRandom(0,fBinSize[pmt]*Float_t(fNBins[pmt]));
 318              Float_t gainVar = fSinglePhESpectrum->GetRandom(0,20)/meansPhE;
 319              Int_t firstBin = TMath::Max(0,(Int_t)((tPhE-kPMRespTime)/fBinSize[pmt]));
 320              Int_t lastBin = TMath::Min(fNBins[pmt]-1,(Int_t)((tPhE+2.*kPMRespTime)/fBinSize[pmt]));
 321              for(Int_t iBin = firstBin; iBin <= lastBin; ++iBin) {
 322                Float_t tempT = fBinSize[pmt]*(0.5+iBin)-tPhE;
 323                fTime[pmt][iBin] += gainVar*charge*fPMResponse->Eval(tempT);
 324              }
 325            }         // ph.e. loop
 326          }           // hit loop
 327      }               // track loop
 328      loader->UnloadHits();
 329   }                  // input loop
 330
 331   Float_t maximum = 0.9*fSignalShape->GetMaximum(0,200); // Not exact, one needs to do this on the convoluted
 332   Float_t integral2 = fSignalShape->Integral(0,200); // function. Anyway the effect is small <10% on the 2.5 ADC thr
 333   for (Int_t ipmt = 0; ipmt < 64; ++ipmt) {
 334     Float_t thr = fCalibData->GetDiscriThr(ipmt)*kChargePerADC*maximum*fBinSize[ipmt]/integral2;
 335     Bool_t ltFound = kFALSE, ttFound = kFALSE;
 336     for (Int_t iBin = 0; iBin < fNBins[ipmt]; ++iBin) {
 337       Float_t t = fBinSize[ipmt]*Float_t(iBin+0.5);
 338       if (fTime[ipmt][iBin] > thr) {
 339         if (!ltFound && (iBin < fNBinsLT[ipmt])) {
 340           ltFound = kTRUE;
 341           fLeadingTime[ipmt] = t;
 342         }
 343       }
 344       else {
 345         if (ltFound) {
 346           if (!ttFound) {
 347             ttFound = kTRUE;
 348             fTimeWidth[ipmt] = t - fLeadingTime[ipmt];
 349           }
 350         }
 351       }
 352       Float_t tadc = t - kADCTimeOffset;
 353       Int_t clock = kNClocks - Int_t(tadc/25.0) - 1;
 354       if (clock >= 0 && clock < kNClocks)
 355         fAdc[ipmt][clock] += fTime[ipmt][iBin]/kChargePerADC;
 356     }
 357     Int_t board = ipmt / 8;
 358     if (ltFound && ttFound) {
 359       fTimeWidth[ipmt] = fCalibData->GetWidthResolution(board)*
 360         Float_t(Int_t(fTimeWidth[ipmt]/fCalibData->GetWidthResolution(board)));
 361       if (fTimeWidth[ipmt] < Float_t(kMinTDCWidth)*fCalibData->GetWidthResolution(board))
 362         fTimeWidth[ipmt] = Float_t(kMinTDCWidth)*fCalibData->GetWidthResolution(board);
 363       if (fTimeWidth[ipmt] > Float_t(kMaxTDCWidth)*fCalibData->GetWidthResolution(board))
 364         fTimeWidth[ipmt] = Float_t(kMaxTDCWidth)*fCalibData->GetWidthResolution(board);
 365     }
 366   }
 367
 368   Int_t evenOrOdd = gRandom->Integer(2);
 369   for (Int_t j=0; j<64; ++j){
 370     for (Int_t iClock = 0; iClock < kNClocks; ++iClock) {
 371       Int_t integrator = (iClock + evenOrOdd) % 2;
 372       fAdc[j][iClock]  += gRandom->Gaus(fAdcPedestal[j][integrator], fAdcSigma[j][integrator]);
 373     }
 374   }
 375
 376   // Now add digits to the digit Tree
 377
 378   for (Int_t i=0; i<64; i++) {
 379     //    printf(" cell %d adc ",i);
 380     //    for (Int_t j = 0; j < kNClocks; ++j)
 381     //      printf("%d ", Int_t(fAdc[i][j]));
 382     //    printf("\n");
 383     Float_t totADC = 0;
 384     for (Int_t j = 8; j <= 11; ++j) {
 385       Int_t tempadc = Int_t(fAdc[i][j]);
 386       if (tempadc > 1023) tempadc = 1023;
 387       Int_t integrator = (j + evenOrOdd) % 2;
 388       if ((Float_t(tempadc) - fAdcPedestal[i][integrator]) > (2.*fAdcSigma[i][integrator]))
 389         totADC += (Float_t(tempadc) - fAdcPedestal[i][integrator]);
 390     }
 391     totADC += fAdcPedestal[i][(10+evenOrOdd)%2];
 392     AddDigit(i, totADC, fLeadingTime[i], fTimeWidth[i], Bool_t((10+evenOrOdd)%2));
 393   }
 394
 395   treeD->Fill();
 396   outLoader->WriteDigits("OVERWRITE");
 397   outLoader->UnloadDigits();
 398   ResetDigit();
 399 }
 400
 401 //____________________________________________________________________________
 402 void AliVZERODigitizer::AddDigit(Int_t PMnumber, Float_t adc, Float_t time, Float_t width, Bool_t integrator)
 403  {
 404
 405 // Adds Digit
 406
 407   TClonesArray &ldigits = *fDigits;
 408
 409   new(ldigits[fNdigits++]) AliVZEROdigit(PMnumber,adc,time,width,kFALSE,kFALSE,integrator);
 410
 411 }
 412 //____________________________________________________________________________
 413 void AliVZERODigitizer::ResetDigit()
 414 {
 415
 416 // Clears Digits
 417
 418   fNdigits = 0;
 419   if (fDigits) fDigits->Delete();
 420 }
 421
 422 //____________________________________________________________________________
 423 AliVZEROCalibData* AliVZERODigitizer::GetCalibData() const
 424
 425 {
 426   AliCDBManager *man = AliCDBManager::Instance();
 427
 428   AliCDBEntry *entry=0;
 429
 430   entry = man->Get("VZERO/Calib/Data");
 431
 432 //   if(!entry){
 433 //     AliWarning("Load of calibration data from default storage failed!");
 434 //     AliWarning("Calibration data will be loaded from local storage ($ALICE_ROOT)");
 435 //     Int_t runNumber = man->GetRun();
 436 //     entry = man->GetStorage("local://$ALICE_ROOT/OCDB")
 437 //       ->Get("VZERO/Calib/Data",runNumber);
 438 //
 439 //   }
 440
 441   // Retrieval of data in directory VZERO/Calib/Data:
 442
 443
 444   AliVZEROCalibData *calibdata = 0;
 445
 446   if (entry) calibdata = (AliVZEROCalibData*) entry->GetObject();
 447   if (!calibdata)  AliFatal("No calibration data from calibration database !");
 448
 449   return calibdata;
 450
 451 }
 452
 453 double AliVZERODigitizer::SignalShape(double *x, double *par)
 454 {
 455   // this function simulates the time
 456   // of arrival of the photons at the
 457   // photocathode
 458   Double_t xx = x[0];
 459   if (xx <= par[0]) return 0;
 460   Double_t a = 1./TMath::Power((xx-par[0])/par[1],1./par[2]);
 461   if (xx <= par[3]) return a;
 462   Double_t b = 1./TMath::Power((xx-par[3])/par[4],1./par[5]);
 463   Double_t f = a*b/(a+b);
 464   AliDebug(100,Form("x=%f func=%f",xx,f));
 465   return f;
 466 }
 467
 468 double AliVZERODigitizer::PMResponse(double *x, double * /* par */)
 469 {
 470   // this function describes the
 471   // PM time response to a single
 472   // photoelectron
 473   Double_t xx = x[0]+kPMRespTime;
 474   return xx*xx*TMath::Exp(-xx*xx/(kPMRespTime*kPMRespTime));
 475 }
 476
 477 double AliVZERODigitizer::SinglePhESpectrum(double *x, double * /* par */)
 478 {
 479   // this function describes the
 480   // PM amplitude response to a single
 481   // photoelectron
 482   Double_t xx = x[0];
 483   if (xx < 0) return 0;
 484   return (TMath::Poisson(xx,kPMNbOfSecElec)+kPMTransparency*TMath::Poisson(xx,1.0));
 485 }
 486
 487 Int_t AliVZERODigitizer::Cell2Pmt(Int_t cell) const
 488 {
 489   // The method maps the scintillator
 490   // indexes to the PM ones
 491   if (cell < 0 || cell >= 80) {
 492     AliError(Form("Wrong VZERO cell index %d",cell));
 493     return -1;
 494   }
 495   if (cell < 16) return cell;
 496   if (cell < 48) return 8 + cell/2;
 497   return cell - 16;
 498 }