class AliTPCCalibCE: public AliTPCCalibRawBase

Implementation of the TPC Central Electrode calibration

Origin: Jens Wiechula, Marian Ivanov   J.Wiechula@gsi.de, Marian.Ivanov@cern.ch





 *                                Class Description                                  *

The AliTPCCalibCE class is used to get calibration data from the Central Electrode using laser runs.

• Time arrival from the CE
• Signal width
• Signal sum

Overview:

1. Working principle
2. User interface for filling data
3. Stored information

I. Working principle

Raw laser data is processed by calling one of the ProcessEvent(...) functions (see below). These in the end call the Update(...) function.

• the Update(...) function:
  In this function the array fPadSignal is filled with the adc signals between the specified range fFirstTimeBin and fLastTimeBin for the current pad. before going to the next pad the ProcessPad() function is called, which analyses the data for one pad stored in fPadSignal.
• the ProcessPad() function:
1. Find Pedestal and Noise information
• use database information which has to be set by calling
  SetPedestalDatabase(AliTPCCalPad *pedestalTPC, AliTPCCalPad *padNoiseTPC)
• if no information from the pedestal data base is available the informaion is calculated on the fly ( see FindPedestal() function )
2. Find local maxima of the pad signal
• maxima arise from the laser tracks, the CE and also periodic postpeaks after the CE signal have have been observed ( see FindLocalMaxima(...) )
3. Find the CE signal information
• to find the position of the CE signal the Tmean information from the previos event is used as the CE signal the local maximum closest to this Tmean is identified
• calculate mean = T0, RMS = signal width and Q sum in a range of -4+7 timebins around Q max position the Q sum is scaled by pad area (see FindPulserSignal(...) function)
4. Fill a temprary array for the T0 information (GetPadTimesEvent(fCurrentSector,kTRUE)) (why see below)
5. Fill the Q sum and RMS values in the histograms (GetHisto[RMS,Q](ROC,kTRUE))

At the end of each event the EndEvent() function is called

• the EndEvent() function:
• calculate the mean T0 for side A and side C. Fill T0 histogram with Time0- This is done to overcome syncronisation problems between the trigger and the fec clock.
• calculate Mean T for each ROC using the COG aroud the median of the LocalMaxima distribution in one sector
• calculate Mean Q
• calculate Global fit parameters for Pol1 and Pol2 fits

After accumulating the desired statistics the Analyse() function has to be called.

• the Analyse() function:
• calculate the mean values of T0, RMS, Q for each pad, using the AliMathBase::GetCOG(...) function
• fill the calibration storage classes (AliTPCCalROC) for each ROC
(The calibration information is stored in the TObjArrays fCalRocArrayT0, fCalRocArrayRMS and fCalRocArrayQ

II. User interface for filling data

To Fill information one of the following functions can be used:

• Bool_t ProcessEvent(eventHeaderStruct *event);
• process Date event
• use AliTPCRawReaderDate and call ProcessEvent(AliRawReader *rawReader)


• Bool_t ProcessEvent(AliRawReader *rawReader);
• process AliRawReader event
• use AliTPCRawStream to loop over data and call ProcessEvent(AliTPCRawStream *rawStream)


• Bool_t ProcessEvent(AliTPCRawStream *rawStream);
• process event from AliTPCRawStream
• call Update function for signal filling


• Int_t Update(const Int_t isector, const Int_t iRow, const Int_t iPad, const Int_t iTimeBin, const Float_t signal);
• directly fill signal information (sector, row, pad, time bin, pad) to the reference histograms

It is also possible to merge two independently taken calibrations using the function

• void Merge(AliTPCCalibSignal *sig)
• copy histograms in 'sig' if they do not exist in this instance
• Add histograms in 'sig' to the histograms in this instance if the allready exist
• After merging call Analyse again!

example: filling data using root raw data:

 
 void fillCE(Char_t *filename)
 {
    rawReader = new AliRawReaderRoot(fileName);
    if ( !rawReader ) return;
    AliTPCCalibCE *calib = new AliTPCCalibCE;
    while (rawReader->NextEvent()){
      calib->ProcessEvent(rawReader);
    }
    calib->Analyse();
    calib->DumpToFile("CEData.root");
    delete rawReader;
    delete calib;
 }
 

III. What kind of information is stored and how to retrieve it

III.1 Stored information

• Histograms:
• For each ROC three TH2S histos 'Reference Histograms' (ROC channel vs. [Time0, signal width, Q sum]) is created when it is filled for the first time (GetHisto[T0,RMS,Q](ROC,kTRUE)). The histos are stored in the TObjArrays fHistoT0Array, fHistoRMSArray and fHistoQArray.


• Calibration Data:
• For each ROC three types of calibration data (AliTPCCalROC) is stored: for the mean arrival Time, the signal width and the signal Sum. The AliTPCCalROC objects are stored in the TObjArrays fCalRocArrayT0, fCalRocArrayRMS , fCalRocArrayQ. The object for each roc is created the first time it is accessed (GetCalRoc[T0,RMS,Q](ROC,kTRUE));


• For each event the following information is stored:
• event time ( TVectorD fVEventTime )
• event id ( TVectorD fVEventNumber )


• mean arrival time for each ROC ( TObjArray fTMeanArrayEvent )
• mean Q for each ROC ( TObjArray fQMeanArrayEvent )
• parameters of a plane fit for each ROC ( TObjArray fParamArrayEventPol1 )
• parameters of a 2D parabola fit for each ROC ( TObjArray fParamArrayEventPol2 )

III.2 Retrieving information

• Accessing the 'Reference Histograms' (Time0, signal width and Q sum information pad by pad):
• TH2F *GetHistoT0(Int_t sector);
• TH2F *GetHistoRMS(Int_t sector);
• TH2F *GetHistoQ(Int_t sector);


• Accessing the calibration storage objects:
• AliTPCCalROC *GetCalRocT0(Int_t sector); // for the Time0 values
• AliTPCCalROC *GetCalRocRMS(Int_t sector); // for the signal width values
• AliTPCCalROC *GetCalRocQ(Int_t sector); // for the Q sum values


• Accessin the event by event information:
• The event by event information can be displayed using the
• MakeGraphTimeCE(Int_t sector, Int_t xVariable, Int_t fitType, Int_t fitParameter)
• which creates a graph from the specified variables

example for visualisation:

  //if the file "CEData.root" was created using the above example one could do the following:
  TFile fileCE("CEData.root")
  AliTPCCalibCE *ce = (AliTPCCalibCE*)fileCE->Get("AliTPCCalibCE");
  ce->GetCalRocT0(0)->Draw("colz");
  ce->GetCalRocRMS(0)->Draw("colz");
  //or use the AliTPCCalPad functionality:
  AliTPCCalPad padT0(ped->GetCalPadT0());
  AliTPCCalPad padSigWidth(ped->GetCalPadRMS());
  padT0->MakeHisto2D()->Draw("colz");       //Draw A-Side Time0 Information
  padSigWidth->MakeHisto2D()->Draw("colz"); //Draw A-Side signal width Information
  //display event by event information:
  //Draw mean arrival time as a function of the event time for oroc sector A00
  ce->MakeGraphTimeCE(36, 0, 2)->Draw("alp");
  //Draw first derivative in local x from a plane fit as a function of the event time for oroc sector A00
  ce->MakeGraphTimeCE(36, 0, 0, 1)->Draw("alp");