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PHOS offline status report. Yuri Kharlov ALICE offline week 16 March 2010. PHOS hardware status in P2. 3 modules (out of 5) are installed in positions 1, 2, 3: 260 <<320, |y|<0.13. 11/12 of FEE is alive and take data (960 channels out of 10752 are dead).

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phos offline status report

PHOS offline status report

Yuri Kharlov

ALICE offline week

16 March 2010

phos hardware status in p2
PHOS hardware status in P2
  • 3 modules (out of 5) are installed in positions 1, 2, 3: 260<<320, |y|<0.13.
  • 11/12 of FEE is alive and take data (960 channels out of 10752 are dead).
  • Noise conditions are satisfactory: 322 channels are noisy
  • PHOS took part in all pp@900 GeV runs (LHC09d) triggered by ALICE minimum bias trigger. Acceptance determines the detector occupancy: about 1/10 of pp collisions have 1 and more clusters.
  • Initial relative calibration of PHOS seems to be at the level 50%. Available physics statistics is not enough to improve calibration.
  • Starting from February 2010, PHOS can produce L0 trigger which allows to suppress empty events (which is 90% of min.bias trigger rate).
    • Statistics collected in test cosmic events is larger than those collected in fall 2009.
    • Regions with sufficiently low trigger thresholds can be calibrated using MIP peak (ongoing)

PHOS offline status

phos das 1
PHOS DAs (1)
  • PHOS had deployed 2 DAs and considered implementing one more:
  • PHOSGAINda.cxx – equalization of mean amplitude in all channels for relative calibration in physics runs (can provide calibration accuracy of 10% -t.b.c. as soon as data is accumulated)
  • PHOSLEDda.cxx – calculation of high-gain/low-gain ratio in LED and physics runs
  • DA for Bad Channel Map – to evaluate quality of signals to map noisy and corrupted channels.
  • Apparently, bad channel map calculation was a rather complicated task. BCM was calculated from 4 sources:
    • Pedestal run: channels with R.M.S. of pedestals above a threshold are noisy
    • LED run with moderate amplitude: channels with deformed signal shape are noisy
    • LED runs with zero amplitude: channels with frequent false signals are noisy
    • Channels with energy deposited considerably larger than surrounding are noisy
    • Offline reconstruction with different bad channel maps allowed to choose the best BCM
  • Online calibration (PHOSGAINda) is affected by BCM: any unsuppressed bad channel can destroy the whole calibration set.

PHOS offline status

phos das 2
PHOS DAs (2)
  • The BCM was calculated manually and was used in all reconstruction passes starting from pass2. It is frozen for the moment.
  • Gain tables was also calculated manually from the photodetector datasheets.
  • The preprocessor procedure has changed:
    • PHOSGAINda and PHOSLEDda are still running. Preprocessor puts the calibration objects to the reference CDB. Preprocessor also does:
      • calculates gains in PHYSICS runs from accumulated statistics and puts them to the production OCDB if Nentrues>1000 and if a channel is not bad. Validity range – 1 run.
      • calculates HG/LG ratio in LED runs is Nentries>2000. Validity range – (run-to-infinity).

PHOS offline status

raw data 1
Raw data (1)
  • Till now, zero suppression has worked with self-calculated pedestals. It turned out that the latency between an external trigger and PHOS readout is not adjusted, the signal shape is deformed
  • Fixed pedestals calculated in a dedicated PEDESTAL run solves the problem with the signal shape.
  • Pedestal DA (PHOSPEDda.cxx) was implemented to create pedestal map. Already in AliRoot trunk. Not deployed in DAQ yet.

PHOS offline status

raw data 2
Raw data (2)
  • PHOS has implemented a series of raw signal fitting: AliPHOSRawFittervX:
    • AliPHOSRawFitterv0 – fast and crude fitter: amplitude is evaluated as a maximum sample, time is calculated from the rising slope of the signal
    • AliPHOSRawFitterv1 – slow fitting based on Tminuit
    • AliPHOSRawFitterv3 – fast fitting based on analytical equations from orthogonality of pseudo-gaussian functions.
    • One more algorithm is being developed
  • Performance comparison (amplitude and time precision) is in progress.
  • CPU consumption comparison:

PHOS offline status

offline calibration
Offline calibration
  • Ultimate calibration is based on pi0 peak width minimization. Implemented as an analysis task, works with ESDs (AliESDCaloClusters and AliESDCaloCells), requires access to PHOS rotation matrices kept in ESD.
  • Calibration with pi0 requires a very large statistics (1 year of data taking). Hence, other calibration methods are looked for: less statistics, worse accuracy.
    • Equalization of APD gains using vendor’s datasheets: used as pre-calibration OCDB, provides 50% decalibration
    • Equalization of photostatistics from LED runs (under progress)
    • Equalization of MIP energy (under progress)
  • Any offline calibration procedure is a subject to validate by the pi0 peak width

PHOS offline status

pi0 peak from lhc09d
Pi0 peak from LHC09d

PHOS offline status

calibration with apd datasheets
Calibration with APD datasheets

Simulated invariant mass spectra with different decalibration level

1: ideal calibration

2: 10% decalibration

3: 20% decalibration

4: 30% decalibration

5: 40% decalibration

6: 50% decalibration

Pre-calibration with APD datasheets gives decalibration 50-%

PHOS offline status

calibration with led runs
Calibration with LED runs

PHOS offline status

calibration with mips
Calibration with MIPs

Cosmic runs 110702, 110832, 110966, 111115 triggered by PHOS TRUs: 450k MIPS found

Cosmic run 91415 triggered by ACORDE+TOF: anti-PHOS trigger.

745 MIPs found out of 5.5M events

PHOS offline status

  • Final (as far as we know) mapping was fixed in December 2009 and put to OCDB
  • 3 PHOS modules have 2 different mappings: module 2 and 3 have the one mapping, the module 4 has another mapping, and all three are different from the old mapping (used before 2009).
  • A decision has been taken to provide 20 mapping files, each file per RCU.
  • Modifications were made in AliCaloRawStreamV3 to apply mapping per module per RCU.

PHOS offline status

phos alignment
PHOS alignment
  • Status has been surveyed in August 2009 just after the installation
  • Survey has provided the following data:
    • coordinates of the PHOS modules in the physicist reference system: displacement up to 1 cm (5 volumes)
    • coordinates of the PHOS strip units in the module local reference system: average displacement is 0.6 mm (1120 volumes)
  • Only PHOS modules misalignment affects physics and willbe provided to the official OCDB
  • Misalignment object is created by MakePHOSFullMisalignment.C. It reads survey table (ascii file) and creates alignment objects.
  • Misalignment is overlaps-free: fiducial gaps between modules were enough for displacements. PHOS structures (cradle, wheels, rails were not surveyed and moved coherently to avoid overlaps.
  • PHOS alignment will be used in pass6 reconstruction.

PHOS offline status

modifications in phos digits
Modifications in PHOS digits
  • Now AliPHOSDigit contains array of ALTRO samples, similar to raw data.
    • Int_tfNSamplesHG; // Number of high-gain ALTRO samples
    • Int_tfNSamplesLG; // Number of low-gain ALTRO samples
    • UShort_t *fSamplesHG; //[fNSamplesHG] Array of high-gain ALTRO samples
    • UShort_t *fSamplesLG; //[fNSamplesLG] Array of low-gain ALTRO samples
  • Summing the digits is performed via summing the samples.

PHOS offline status

track matching in lhc09d x b 0 5t
Track matching in LHC09d: X, B=0.5T

spos~sneg=4 cm

PHOS offline status

track matching in lhc09d z b 0 5t
Track matching in LHC09d: Z, B=0.5T

spos~sneg=2.1 cm

PHOS offline status

track matching with b 0 runs 105143 104160
Track matching with B=0 (runs 105143, 104160)

PHOS alignment is consistent with track extrapolation within 0.5 cm. This is of order of TPC decalibration seen as difference in offsets in + and - z.

PHOS offline status

planning simulation
Planning: Simulation

PHOS offline status

planning qa
Planning: QA

PHOS offline status

planning trigger
Planning: Trigger

PHOS offline status