Major fixes to the raw-data simulation. The ADC samples and signal width are added...
[u/mrichter/AliRoot.git] / VZERO / AliVZERODigitizer.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 /* $Id$ */
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   fSignalShape->SetParameters(-1.07335e+00,2.16002e+01,-1.26133e-01,
82                               1.41619e+00,5.50334e-01,3.86111e-01);
83
84   fPMResponse = new TF1("VZEROPMResponse",this,&AliVZERODigitizer::PMResponse,-kPMRespTime,2.*kPMRespTime,0,"AliVZERODigitizer","PMResponse");
85   fSinglePhESpectrum = new TF1("VZEROSinglePhESpectrum",this,&AliVZERODigitizer::SinglePhESpectrum,0,20,0,"AliVZERODigitizer","SinglePhESpectrum");
86
87   // Now get the CTP L0->L1 delay
88   AliCDBEntry *entry = AliCDBManager::Instance()->Get("GRP/CTP/CTPtiming");
89   if (!entry) AliFatal("CTP timing parameters are not found in OCDB !");
90   AliCTPTimeParams *ctpParams = (AliCTPTimeParams*)entry->GetObject();
91   Float_t l1Delay = (Float_t)ctpParams->GetDelayL1L0()*25.0;
92
93   AliCDBEntry *entry2 = AliCDBManager::Instance()->Get("VZERO/Calib/TimeDelays");
94   if (!entry2) AliFatal("VZERO time delays are not found in OCDB !");
95   TH1F *delays = (TH1F*)entry2->GetObject();
96
97   for(Int_t i = 0 ; i < 64; ++i) {
98
99     for(Int_t j = 0; j < kNClocks; ++j) fAdc[i][j] = 0;
100     fLeadingTime[i] = fTimeWidth[i] = 0;
101
102     fPmGain[i] = fCalibData->GetGain(i);
103
104     fAdcPedestal[i][0] = fCalibData->GetPedestal(i);
105     fAdcSigma[i][0]    = fCalibData->GetSigma(i); 
106     fAdcPedestal[i][1] = fCalibData->GetPedestal(i+64);
107     fAdcSigma[i][1]    = fCalibData->GetSigma(i+64); 
108
109     Int_t board = AliVZEROCalibData::GetBoardNumber(i);
110     fNBins[i] = TMath::Nint(((Float_t)(fCalibData->GetMatchWindow(board)+1)*25.0+
111                              (Float_t)kMaxTDCWidth*fCalibData->GetWidthResolution(board))/
112                             fCalibData->GetTimeResolution(board));
113     fNBinsLT[i] = TMath::Nint(((Float_t)(fCalibData->GetMatchWindow(board)+1)*25.0)/
114                               fCalibData->GetTimeResolution(board));
115     fBinSize[i] = fCalibData->GetTimeResolution(board);
116     fHptdcOffset[i] = (((Float_t)fCalibData->GetTriggerCountOffset(board)-
117                         (Float_t)fCalibData->GetRollOver(board))*25.0+
118                        fCalibData->GetTimeOffset(i)+
119                        l1Delay+
120                        delays->GetBinContent(i+1)+
121                        kV0Offset);
122
123     fTime[i] = new Float_t[fNBins[i]];
124     memset(fTime[i],0,fNBins[i]*sizeof(Float_t));
125   }
126
127 }
128
129 //____________________________________________________________________________ 
130   AliVZERODigitizer::AliVZERODigitizer(AliRunDigitizer* manager)
131                     :AliDigitizer(manager),
132                      fCalibData(GetCalibData()),
133                      fPhotoCathodeEfficiency(0.18),
134                      fNdigits(0),
135                      fDigits(0),
136                      fSignalShape(NULL),
137                      fPMResponse(NULL),
138                      fSinglePhESpectrum(NULL)
139                                         
140 {
141   // constructor
142   // Initialize OCDB and containers used in the digitization
143   
144   fSignalShape = new TF1("VZEROSignalShape",this,&AliVZERODigitizer::SignalShape,0,200,6,"AliVZERODigitizer","SignalShape");
145   //  fSignalShape->SetParameters(0,1.57345e1,-4.25603e-1,2.9,6.40982,3.69339e-01);
146   //  fSignalShape->SetParameters(1.34330e+00,1.13007e+02,-4.95705e-01,
147   //                          3.68911e+00,1.01040e+00, 3.94675e-01);
148   fSignalShape->SetParameters(-1.07335e+00,2.16002e+01,-1.26133e-01,
149                               1.41619e+00,5.50334e-01,3.86111e-01);
150   fPMResponse = new TF1("VZEROPMResponse",this,&AliVZERODigitizer::PMResponse,-kPMRespTime,2.*kPMRespTime,0,"AliVZERODigitizer","PMResponse");
151   fSinglePhESpectrum = new TF1("VZEROSinglePhESpectrum",this,&AliVZERODigitizer::SinglePhESpectrum,0,20,0,"AliVZERODigitizer","SinglePhESpectrum");
152   
153   // Now get the CTP L0->L1 delay
154   AliCDBEntry *entry = AliCDBManager::Instance()->Get("GRP/CTP/CTPtiming");
155   if (!entry) AliFatal("CTP timing parameters are not found in OCDB !");
156   AliCTPTimeParams *ctpParams = (AliCTPTimeParams*)entry->GetObject();
157   Float_t l1Delay = (Float_t)ctpParams->GetDelayL1L0()*25.0;
158
159   AliCDBEntry *entry2 = AliCDBManager::Instance()->Get("VZERO/Calib/TimeDelays");
160   if (!entry2) AliFatal("VZERO time delays are not found in OCDB !");
161   TH1F *delays = (TH1F*)entry2->GetObject();
162
163   for(Int_t i = 0 ; i < 64; ++i) {
164
165     for(Int_t j = 0; j < kNClocks; ++j) fAdc[i][j] = 0;
166     fLeadingTime[i] = fTimeWidth[i] = 0;
167
168     fPmGain[i] = fCalibData->GetGain(i);
169
170     fAdcPedestal[i][0] = fCalibData->GetPedestal(i);
171     fAdcSigma[i][0]    = fCalibData->GetSigma(i); 
172     fAdcPedestal[i][1] = fCalibData->GetPedestal(i+64);
173     fAdcSigma[i][1]    = fCalibData->GetSigma(i+64); 
174
175     Int_t board = AliVZEROCalibData::GetBoardNumber(i);
176     fNBins[i] = TMath::Nint(((Float_t)(fCalibData->GetMatchWindow(board)+1)*25.0+
177                              (Float_t)kMaxTDCWidth*fCalibData->GetWidthResolution(board))/
178                             fCalibData->GetTimeResolution(board));
179     fNBinsLT[i] = TMath::Nint(((Float_t)(fCalibData->GetMatchWindow(board)+1)*25.0)/
180                               fCalibData->GetTimeResolution(board));
181     fBinSize[i] = fCalibData->GetTimeResolution(board);
182     fHptdcOffset[i] = (((Float_t)fCalibData->GetTriggerCountOffset(board)-
183                         (Float_t)fCalibData->GetRollOver(board))*25.0+
184                        fCalibData->GetTimeOffset(i)+
185                        l1Delay+
186                        delays->GetBinContent(i+1)+
187                        kV0Offset);
188
189     fTime[i] = new Float_t[fNBins[i]];
190     memset(fTime[i],0,fNBins[i]*sizeof(Float_t));
191   }
192 }
193            
194 //____________________________________________________________________________ 
195   AliVZERODigitizer::~AliVZERODigitizer()
196 {
197   // destructor
198   
199   if (fDigits) {
200     fDigits->Delete();
201     delete fDigits;
202     fDigits=0; 
203   }
204
205   if (fSignalShape) {
206     delete fSignalShape;
207     fSignalShape = NULL;
208   }
209   if (fPMResponse) {
210     delete fPMResponse;
211     fPMResponse = NULL;
212   }
213   if (fSinglePhESpectrum) {
214     delete fSinglePhESpectrum;
215     fSinglePhESpectrum = NULL;
216   }
217
218   for(Int_t i = 0 ; i < 64; ++i) {
219     if (fTime[i]) delete [] fTime[i];
220   }
221 }
222
223 //_____________________________________________________________________________
224 Bool_t AliVZERODigitizer::Init()
225 {
226   // Initialises the digitizer
227
228   // Initialises the Digit array
229   fDigits = new TClonesArray ("AliVZEROdigit", 1000);
230   
231   return kTRUE;
232 }
233
234 //____________________________________________________________________________
235 void AliVZERODigitizer::Exec(Option_t* /*option*/) 
236 {   
237   // Creates digits from hits
238   fNdigits     =    0;  
239
240   Int_t labels[64][3];
241   for(Int_t i = 0 ; i < 64; ++i) {
242     memset(fTime[i],0,fNBins[i]*sizeof(Float_t));
243     for(Int_t j = 0; j < kNClocks; ++j) fAdc[i][j] = 0;
244     fLeadingTime[i] = fTimeWidth[i] = 0;
245     labels[i][0] = labels[i][1] = labels[i][2] = -1;
246   }
247   Float_t integral = fPMResponse->Integral(-kPMRespTime,2.*kPMRespTime);
248   Float_t meansPhE = fSinglePhESpectrum->Mean(0,20);
249
250   AliRunLoader* outRunLoader =  AliRunLoader::GetRunLoader(fManager->GetOutputFolderName());    
251   if (!outRunLoader) {
252     Error("Exec", "Can not get output Run Loader");
253     return;
254   }
255     
256   AliLoader* outLoader = outRunLoader->GetLoader("VZEROLoader");
257
258   if (!outLoader) {
259     Error("Exec", "Can not get output VZERO Loader");
260     return;
261   }
262
263   const char* mode = "update";
264   if(outRunLoader->GetEventNumber() == 0) mode = "recreate";
265   outLoader->LoadDigits(mode);
266
267   if (!outLoader->TreeD()) outLoader->MakeTree("D");
268   outLoader->MakeDigitsContainer();
269   TTree* treeD  = outLoader->TreeD();
270   Int_t bufsize = 16000;
271   treeD->Branch("VZERODigit", &fDigits, bufsize); 
272   
273   for (Int_t iInput = 0; iInput < fManager->GetNinputs(); iInput++) {
274      AliRunLoader* runLoader = AliRunLoader::GetRunLoader(fManager->GetInputFolderName(iInput));
275      AliLoader* loader = runLoader->GetLoader("VZEROLoader");
276      if (!loader) {
277        Error("Exec", "Can not get VZERO Loader for input %d", iInput);
278        continue;
279          }
280       
281      if (!runLoader->GetAliRun()) runLoader->LoadgAlice();
282
283      AliVZERO* vzero = (AliVZERO*) runLoader->GetAliRun()->GetDetector("VZERO");
284      if (!vzero) {
285        Error("Exec", "No VZERO detector for input %d", iInput);
286        continue;
287          }
288       
289      loader->LoadHits();
290      TTree* treeH = loader->TreeH();
291      if (!treeH) {
292        Error("Exec", "Cannot get TreeH for input %d", iInput);
293        continue; 
294          }
295        
296      TClonesArray* hits = vzero->Hits();
297
298      //     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};
299      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};
300 //  Now makes Digits from hits
301      Int_t nTracks = (Int_t) treeH->GetEntries();
302      for (Int_t iTrack = 0; iTrack < nTracks; iTrack++) {
303          vzero->ResetHits();
304          treeH->GetEvent(iTrack);
305          Int_t nHits = hits->GetEntriesFast();
306          for (Int_t iHit = 0; iHit < nHits; iHit++) {
307            AliVZEROhit* hit = (AliVZEROhit *)hits->UncheckedAt(iHit);
308            Int_t nPhot = hit->Nphot();
309            Int_t cell  = hit->Cell();                          
310            Int_t pmt = Cell2Pmt(cell);
311            Int_t trackLabel = hit->GetTrack();
312            for(Int_t l = 0; l < 3; ++l) {
313              if (labels[pmt][l] < 0) {
314                labels[pmt][l] = trackLabel;
315                break;
316              }
317            }
318            Float_t dt_scintillator = gRandom->Gaus(0,kIntTimeRes);
319            Float_t t = dt_scintillator + 1e9*hit->Tof();
320            if (pmt < 32) t += kV0CDelayCables;
321            t += fHptdcOffset[pmt];
322            Int_t nPhE;
323            Float_t prob = lightYieldCorr[pmt]*fPhotoCathodeEfficiency; // Optical losses included!
324            if (nPhot > 100)
325              nPhE = (Int_t)gRandom->Gaus(prob*Float_t(nPhot)+0.5,
326                                          sqrt(Float_t(nPhot)*prob*(1.-prob)));
327            else
328              nPhE = gRandom->Binomial(nPhot,prob);
329            Float_t charge = TMath::Qe()*fPmGain[pmt]*fBinSize[pmt]/integral;
330            for (Int_t iPhE = 0; iPhE < nPhE; ++iPhE) {
331              Float_t tPhE = t + fSignalShape->GetRandom(0,fBinSize[pmt]*Float_t(fNBins[pmt]));
332              Float_t gainVar = fSinglePhESpectrum->GetRandom(0,20)/meansPhE;
333              Int_t firstBin = TMath::Max(0,(Int_t)((tPhE-kPMRespTime)/fBinSize[pmt]));
334              Int_t lastBin = TMath::Min(fNBins[pmt]-1,(Int_t)((tPhE+2.*kPMRespTime)/fBinSize[pmt]));
335              for(Int_t iBin = firstBin; iBin <= lastBin; ++iBin) {
336                Float_t tempT = fBinSize[pmt]*(0.5+iBin)-tPhE;
337                fTime[pmt][iBin] += gainVar*charge*fPMResponse->Eval(tempT);
338              }
339            }         // ph.e. loop
340          }           // hit loop
341      }               // track loop
342      loader->UnloadHits();
343   }                  // input loop
344
345   Float_t maximum = 0.9*fSignalShape->GetMaximum(0,200); // Not exact, one needs to do this on the convoluted
346   Float_t integral2 = fSignalShape->Integral(0,200); // function. Anyway the effect is small <10% on the 2.5 ADC thr
347   for (Int_t ipmt = 0; ipmt < 64; ++ipmt) {
348     Float_t thr = fCalibData->GetDiscriThr(ipmt)*kChargePerADC*maximum*fBinSize[ipmt]/integral2;
349     Bool_t ltFound = kFALSE, ttFound = kFALSE;
350     for (Int_t iBin = 0; iBin < fNBins[ipmt]; ++iBin) {
351       Float_t t = fBinSize[ipmt]*Float_t(iBin);
352       if (fTime[ipmt][iBin] > thr) {
353         if (!ltFound && (iBin < fNBinsLT[ipmt])) {
354           ltFound = kTRUE;
355           fLeadingTime[ipmt] = t;
356         }
357       }
358       else {
359         if (ltFound) {
360           if (!ttFound) {
361             ttFound = kTRUE;
362             fTimeWidth[ipmt] = t - fLeadingTime[ipmt];
363           }
364         }
365       }
366       Float_t tadc = t - kClockOffset - fCalibData->GetTimeOffset(ipmt);
367       Int_t clock = kNClocks/2 - Int_t(tadc/25.0);
368       if (clock >= 0 && clock < kNClocks)
369         fAdc[ipmt][clock] += fTime[ipmt][iBin]/kChargePerADC;
370     }
371     Int_t board = AliVZEROCalibData::GetBoardNumber(ipmt);
372     if (ltFound && ttFound) {
373       fTimeWidth[ipmt] = fCalibData->GetWidthResolution(board)*
374         Float_t(Int_t(fTimeWidth[ipmt]/fCalibData->GetWidthResolution(board)));
375       if (fTimeWidth[ipmt] < Float_t(kMinTDCWidth)*fCalibData->GetWidthResolution(board))
376         fTimeWidth[ipmt] = Float_t(kMinTDCWidth)*fCalibData->GetWidthResolution(board);
377       if (fTimeWidth[ipmt] > Float_t(kMaxTDCWidth)*fCalibData->GetWidthResolution(board))
378         fTimeWidth[ipmt] = Float_t(kMaxTDCWidth)*fCalibData->GetWidthResolution(board);
379     }
380   }
381
382   Int_t evenOrOdd = gRandom->Integer(2);
383   for (Int_t j=0; j<64; ++j){
384     for (Int_t iClock = 0; iClock < kNClocks; ++iClock) {
385       Int_t integrator = (iClock + evenOrOdd) % 2;
386       fAdc[j][iClock]  += gRandom->Gaus(fAdcPedestal[j][integrator], fAdcSigma[j][integrator]);
387     }
388   }
389         
390   // Now add digits to the digit Tree 
391
392   Short_t *chargeADC = new Short_t[kNClocks];
393   for (Int_t i=0; i<64; i++) {      
394     Float_t totADC = 0;
395     for (Int_t j = 0; j < kNClocks; ++j) {
396       Int_t tempadc = Int_t(fAdc[i][j]);
397       if (tempadc > 1023) tempadc = 1023;
398       chargeADC[j] = tempadc;
399       if (j >= 8 && j <= 11) {
400         Int_t integrator = (j + evenOrOdd) % 2;
401         if ((Float_t(tempadc) - fAdcPedestal[i][integrator]) > (2.*fAdcSigma[i][integrator]))
402           totADC += (Float_t(tempadc) - fAdcPedestal[i][integrator]);
403       }
404     }
405     totADC += fAdcPedestal[i][(10+evenOrOdd)%2];
406     AddDigit(i, totADC, fLeadingTime[i], fTimeWidth[i], Bool_t((10+evenOrOdd)%2), chargeADC, labels[i]);
407   }
408   delete [] chargeADC;
409
410   treeD->Fill();
411   outLoader->WriteDigits("OVERWRITE");  
412   outLoader->UnloadDigits();     
413   ResetDigit();
414 }
415
416 //____________________________________________________________________________
417 void AliVZERODigitizer::AddDigit(Int_t PMnumber, Float_t adc, Float_t time, Float_t width, Bool_t integrator, Short_t *chargeADC, Int_t *labels) 
418  { 
419  
420 // Adds Digit 
421  
422   TClonesArray &ldigits = *fDigits;  
423          
424   new(ldigits[fNdigits++]) AliVZEROdigit(PMnumber,adc,time,width,integrator,chargeADC,labels);
425          
426 }
427 //____________________________________________________________________________
428 void AliVZERODigitizer::ResetDigit()
429 {
430
431 // Clears Digits
432
433   fNdigits = 0;
434   if (fDigits) fDigits->Delete();
435 }
436
437 //____________________________________________________________________________
438 AliVZEROCalibData* AliVZERODigitizer::GetCalibData() const
439
440 {
441   AliCDBManager *man = AliCDBManager::Instance();
442
443   AliCDBEntry *entry=0;
444
445   entry = man->Get("VZERO/Calib/Data");
446
447 //   if(!entry){
448 //     AliWarning("Load of calibration data from default storage failed!");
449 //     AliWarning("Calibration data will be loaded from local storage ($ALICE_ROOT)");
450 //     Int_t runNumber = man->GetRun();
451 //     entry = man->GetStorage("local://$ALICE_ROOT/OCDB")
452 //       ->Get("VZERO/Calib/Data",runNumber);
453 //      
454 //   }
455
456   // Retrieval of data in directory VZERO/Calib/Data:
457
458
459   AliVZEROCalibData *calibdata = 0;
460
461   if (entry) calibdata = (AliVZEROCalibData*) entry->GetObject();
462   if (!calibdata)  AliFatal("No calibration data from calibration database !");
463
464   return calibdata;
465
466 }
467
468 double AliVZERODigitizer::SignalShape(double *x, double *par)
469 {
470   // this function simulates the time
471   // of arrival of the photons at the
472   // photocathode
473   Double_t xx = x[0];
474   if (xx <= par[0]) return 0;
475   Double_t a = 1./TMath::Power((xx-par[0])/par[1],1./par[2]);
476   if (xx <= par[3]) return a;
477   Double_t b = 1./TMath::Power((xx-par[3])/par[4],1./par[5]);
478   Double_t f = a*b/(a+b);
479   AliDebug(100,Form("x=%f func=%f",xx,f));
480   return f;
481 }
482
483 double AliVZERODigitizer::PMResponse(double *x, double * /* par */)
484 {
485   // this function describes the
486   // PM time response to a single
487   // photoelectron
488   Double_t xx = x[0]+kPMRespTime;
489   return xx*xx*TMath::Exp(-xx*xx/(kPMRespTime*kPMRespTime));
490 }
491
492 double AliVZERODigitizer::SinglePhESpectrum(double *x, double * /* par */)
493 {
494   // this function describes the
495   // PM amplitude response to a single
496   // photoelectron
497   Double_t xx = x[0];
498   if (xx < 0) return 0;
499   return (TMath::Poisson(xx,kPMNbOfSecElec)+kPMTransparency*TMath::Poisson(xx,1.0));
500 }
501
502 Int_t AliVZERODigitizer::Cell2Pmt(Int_t cell) const
503 {
504   // The method maps the scintillator
505   // indexes to the PM ones
506   if (cell < 0 || cell >= 80) {
507     AliError(Form("Wrong VZERO cell index %d",cell));
508     return -1;
509   }
510   if (cell < 16) return cell;
511   if (cell < 48) return 8 + cell/2;
512   return cell - 16;
513 }