PHOS calibration and alignment. Yuri Kharlov IHEP, Protvino ALICE off-line week 22 February 2005. Outline. Calibration Pre-calibration by wide e - beam Run-time calibration procedures Calibration data structure Alignment Dead/bad channels. Questionnaire.
ALICE off-line week
22 February 2005
PHOS has 5 modules
Each module consists of EMC and CPV
1 EMC module contains 3584 crystals
1 CPV module contains 7168 pads
AliPHOSEmcCalibrationCoefficient:Float_t fCalibrationCoefficient[nEmc]; // convertion from ADC counts to GeV Float_t fAltroFitParam[2,nEmc]; // two parameters of the signal shape fit TDatetime fTimeStamp; // time stamp when the coefficient was measured AliPHOSCpvCalibrationCoefficient:Float_t fCalibrationCoefficient[nCpv]; // convertion from ADC counts to GeV Float_t fPedestal[nCpv]; // pedestal in ADC counts TDatetime fTimeStamp; // time stamp when the coefficient was measured These classes will contain the methods to set and to get the calibration parameters by the absolute channel number, as well as by the relative channel number (module, row, column). The actual dimensions of arrays fCalibrationCoefficient[nEmc] and fCalibrationCoefficient[nCpv] correspond to the number of crystals in PHOS (nEmc=17920) and the number of pads in CPV (nCpv=35840).
AliPHOSEmcAlignment:Float_t fIp2EmcDistance; // distance from IP to the center of each of 5 EMC modules Float_t fEmcCenterDirection[3,5]; // direction of each of 5 EMC modules seen from IP TMatrixD fEmcOrientation; // Rotation matrix of each of 5 EMC modules in MARS
AliPHOSCpvAlignment:Float_t fIp2CpvDistance; // distance from IP to the center of each of 5 CPV modules Float_t fECpvCenterDirection[3,5]; // direction of each of 5 CPV modules seen from IP TMatrixD fCpvOrientation; // Rotation matrix of each of 5 CPV modules in MARS
AliPHOSBadChannels: Int_t fNEmcBad; // number of EMC bad channels Int_t fNCpvBad; // number of CPV bad channels Int_t fEmcBadChannel(nEmcBad); // Array of EMC bad channel absolute indices Int_t fCpvBadChannel(nCpvBad); // Array of CPV bad channel absolute indices AliPHOSDeadChannels:Int_t fNEmcDead; // number of EMC dead channels Int_t fNCpvDead; // number of CPV dead channels Int_t fEmcDeadChannel(nEmcDead); // Array of EMC dead channel absolute indices Int_t fCpvDeadChannel(nCpvDead); // Array of CPV dead channel absolute indices The classes AliPHOSBadChannels and AliPHOSDeadChannels keep the list of bad and dead channel indices. The array dimensions nEmcBad, nCpvBad, nEmcDead, nCpvDead can be foreseen now as 10% of the total channel number, but real life will correct these dimensions.
Sources of calibration/bad-dead/alignment data can be distinguished to initial data and run-time data.
From the object definitions above, the size of the object are as follows:
PHOS module should be exposed by a wide electron beam at fixed known energy E0
Calibration coefficients ai are found from minimization of the functional
Total deposited energy is summed over 5x5 area around the max. cell
Calibration after 3d interation
Calibration after 3d iteration
after 1st interation
after 2d interation
after 3d interation
Da/a = 0.18%
200,000 central Pb-Pb events (4 minutes of LHC run)
Calibration coefficients can be found by minimization of p0 mass.
It requires low combinatorial background high pT longer exposition.
pT>5 GeV is a lower limit for this calibration.
To calibrate each cell with 1000-event statistics one needs 10 days.
EMC can be calibrated by tracks found by the global tracking procedure and identified as electrons (similar to calibration by e- beam)
Where Eiis electron energy in event i.
Needed statistics is to be estimated yet.
PHOS will be polulated by photons distributed uniformly vs X,Y.
On average there will be 10 reconstructed photons per module per one central Pb-Pb collision.
Mean rec.photon energy can serve as a measure of calibration.
To store statistics of 1000 events per channel needed for calibration, one needs 5 minutes of LHC run.
CPV responds to charged particles passing through CPV gas volume. On average there will be 100 charged particles per module per one central Pb-Pb collision.
Similar to PHOS EMC, CPV fired pads will be distributed uniformly vs X,Y.
Pad response function (induced charged) can serve as a measure of calibration.
To store statistics of 1000 events per pad needed for calibration, one needs <1 minute of LHC run.