PHOS offline status report

Yuri KharlovALICE offline week

6 July 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 are alive and take data (960 channels out of

10752 are dead).• Noise conditions are satisfactory: 410 channels are noisy• Energy scale is 2 MeV/ADC instead of 5 designed MeV/ADC.

The maximum measurable energy is 30 GeV instead of 100 GeV.

• PHOS took part in all pp runs (LHC10b,c,d) triggered by ALICE minimum bias trigger.

• Initial relative calibration of PHOS seemed to be at the level 20% in modules 2 and 3, 50% in module 4.

6 July 2010 PHOS offline status 2

Fixed bugs in reconstruction• AliPHOSRawFitterv0: wrong treatment of low-gain amplitudes.

https://savannah.cern.ch/bugs/?68008

6 July 2010 PHOS offline status 3

• AliPHOSClustertizerv1: wrong application of calibration parameters to clusters. All cells in a cluster were calibrated with one and the same calibration parameter of the cluster seed. https://savannah.cern.ch/bugs/?68375

• Starting from v4-18-Rev-20, PHOS bugs were fixed. Used in pass2 reco.

PHOS DAs 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 PHOSLEDda.cxx – calculation of high-gain/low-gain ratio in LED and

physics runs Apparently, bad channel map calculation is 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

6 July 2010 PHOS offline status 4

Usage of online DA’s in PHOS• Change in preprocessor procedure: 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).

• Although 2 DA’s are running, their affect to the PHOS conditions is very limited:– Mapping the bad channels cannot be an automatic procedure, requires a

human intervention and decision.– Noise appears and disappears. It can suddenly destroy firm calibration– Preprocessors simply copies gains and HG/LG ratios from the previous run,

unless a very large statistics per run is accumulated.• We rely on conditions calculated offline only.

6 July 2010 PHOS offline status 5

Offline calibration• Offline calibration is implemented as an analysis task and works with ESD

or AOD. Requires the full available statistics.• Calibration algorithms:

– Accumulating the cell energy histograms (10752 TH1F histograms): to search bad channels and to calculate mean deposited energy

– Equalization of the mean deposited energy– Equalization of the number of hits per channel– Equalization of photostatistics from LED runs– pi0 peak width minimization. Implemented as an analysis task.

• Calibration with pi0 requires a very large statistics (1 year of data taking). Hence, other calibration methods are looked for: less statistics, worse accuracy.

• Any offline calibration procedure is a subject to validate by the pi0 peak width

6 July 2010 PHOS offline status 6

Equalization of the mean cell energies:Data and software

PHOS has requested 4 custom reconstructions of LHC10b,c (10-90 Mio events) to calculate the calibration parameters• Reco of LHC10c production ID PHOS_calib

(http://alimonitor.cern.ch?75, AliRoot v4-18-Rev-20, 73 Mevents) was used to run offline calibration

• Reco of LHC10c production ID PHOS_calib3 (http://alimonitor.cern.ch?84, AliRoot v4-18-Rev-20, 89 Mevents) was used to verify the new calibration

6 July 2010 7PHOS offline status

Recalibration performance

6 July 2010 8PHOS offline status

Module 1Module 3

Module 2

Several iterations (from 2 to 6) were enough to improve the pi0 peak width from 15 MeV to 9 MeV.

Recalibration of the worst module 4: before...

6 July 2010 9PHOS offline status

Recalibration of the worst module 4: after...

6 July 2010 10PHOS offline status

PHOS offline status 11/

May 2010: inv.mass from reconstruction• Module 1 was quite bad compared to module 2

and 3.• m (1) = 122 MeV/c2, (1) = 30 MeV/c2

• m (2-3) = 134 MeV/c2, (2-3) = 17 MeV/c2

• Until improved calibration of module 1, need to discard it from the analysis

6 July 2010

Module 1

Module 2

Module 3

PHOS offline status 12

July 2010: Invariant mass from reconstruction

Now all 3 modules are equally well calibrated.

6 July 2010

PHOS offline status 13

Latest reconstruction: LHC10c pass2

All 3 PHOS modules

6 July 2010

PHOS offline status 14

Inv.mass vs pt in LHC10c pass2 reco

6 July 2010

PHOS offline status 15

May 2010: 0 peak mass and width vs pt

6 July 2010

0 peak width varied from 17 to 13 MeV/c2

PHOS offline status 16

July 2010: 0 peak mass and width vs pt

6 July 2010

0 peak width varied from 11 to 9 MeV/c2

Correlation between iterations

6 July 2010 17PHOS offline status

How decalibration affects 0 peak width

6 July 2010 PHOS offline status 18

1: ideal calibration2: 10% decalibration3: 20% decalibration4: 30% decalibration5: 40% decalibration6: 50% decalibration

Simulated invariant mass spectra with different decalibration level

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 will be 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 is used in reconstruction.

6 July 2010 PHOS offline status 19

Todo list for the nearest future• Further calibration improvement: the goal to achieve

3% decalibration• Bad channel map refining• Raw spectrum fitting• QA checker implementation• QA reference data• Improvement in PHSQA AMORE agent• TRU (fake ALTRO) data decoding• PHOS L0 trigger configuration and input to CTP

6 July 2010 PHOS offline status 20