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PHOS offline status report
Dmitri Peressounko
ALICE offline week, 15.11.2010
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PHOS offline status 2
Reconstruction status• Raw data reconstruction: – Fast fitting with GammaN is implemented. No much
improvement neither in Amp, no by using c2 cut => do not use.
– Correction for a time stamp by the L1 phase read out of ALTRO trailer.
• Time gate was introduced to RecoParameters and to Clusterizer to suppress noise. Not used by default, still under investigation.
• More flexibility on non-linearity correction added: one can choose functional form and parameters from OCDB. Default values not changed yet.
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PHOS offline status 3
Online DQM• PHOS data quality monitor is implemented as QA
AMORE agent.• For the DQM shifter a single histogram is shown:
the number of cells per event.• In pp run the physics events are rare, hence the
number of cells is determined by noisy channels.• In Pb-Pb run the occupancy of the PHOS detector
may be high, so the number of cells is determined by the sum of noise and physics signals.
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PHOS offline status 4
PHOS OCDB objects• Energy calibration: conversion from ADC
counts to GeV• High gain/low gain ratio• Bad channel map• Alignment• Reconstruction parameters• All objects are produced offline
15.11.2010
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PHOS offline status 5
PHOS energy calibration• Pre-calibration: adjusting the high-voltage APD bias to provide the same
APD gain for all channels. Achieved calibration accuracy: 20-50%;
• Physics data with pp collisions allowed to improve calibration using equalization of the mean deposited energy per channel from physics events. Achieved calibration accuracy: 6.5%;
• Final calibration will be finalized using equalization of the 0 peak per channel. Accumulated statistics is still not enough for it. The goal is to achieve calibration accuracy of 1%.
• Difference between pass1 and pass2 reconstructions for PHOS:
– LHC10b: pass1, pass2 – both initial calibration
– LHC10c: pass1 – raw calibration, pass2 – latest calibration
– LHC10d: pass1 was corrupted due to OCDB error can’t be used, pass 2 OK
– LHC10f, g: latest calibration in both passes15.11.2010
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PHOS offline status 6
Calibration with <E>
15.11.2010
For each PHOS cell calculate mean energy <Ei> in the range E>0.06 GeV
Calculate corrections to the CC: Ci = const/<Ei>, where const was adjusted to put π0 peak to 135 MeV/c2.
Use Ci to calculate <Ei> of the next iteration: recalibrate cell energy with Ci
recalculate energy and position of the cluster Calibration was found on 70M event sample
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PHOS offline status 7
Module 4 before calibration
15.11.2010
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PHOS offline status 8
Module 4 after calibration
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PHOS offline status 9
PHOS HG/LG calibration• PHOS FEE measures energy by 2 ADCs with different gains:
• High gain: 2 MeV – 2 GeV, 10 bits
• Low gain: 32 MeV – 32 GeV, 10 bits
• Ratio HG/LG may vary from channel to channel.
• Precise value HG/LG is needed to ensure a continues spectrum in the whole range 2 MeV – 32 GeV
• HG/LG was measured in dedicated LED runs with variable amplitudes.
• HG/LG is a property of the electric circuit and cannot change in time. One high-statistics LED run is enough to calculate it once and forever.
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PHOS offline status 10
HG/LG measurements
15.11.2010
• HG/LG ratio varies within RMS 2%.• Mean value is different in module 4 compared with modules 2 and 3.
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PHOS offline status 11
Bad channel map
15.11.2010
Bad channel map was found off-line from different sources of information:
• Pedestal runs
• LED runs with variable amplitude
• LED runs with zero amplitude
• Physics runs
In total 1371 channels are bad (out of 10752)
All threePedestal+QualityQuality+NoiseQualityPedestalNoise
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PHOS offline status 12
Track Matching, LHC10c pass2 dz vs z
No slope in dz(z) distribution. Still there is some jump between + and – z: 0.33 cm for mod.3 and 0.2 cm for mod 4. (residual TPC decalibration + TPC sector dependence?)15.11.2010
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PHOS offline status 13
Track Matching, LHC10c pass2, phi
No unique slope for all distributions. Overall offsets: Module 2: -0.7 cm; Module 3: -0.8 cm; Module 4: -0.9 cm 15.11.2010
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PHOS performance in pp 14
Timing: Pileup
8.11.2010
Runs analyzed (LHC10e): 130795,130799,130802,130803,130834,130842,130844,130848,130850
Wrong bands disappear if PhysicsSelection +Zvtx cut applyedPileup:
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PHOS performance in pp 15
Timing: L1phase shift
8.11.2010
Subtracting:EMCAL/TPC
Adding:PHOS
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Timing: L1phase shift - Side peaks
Single peak at 0
Single peak at -1
Single peak at +1
2 peaks at -1,0
2 peaks at 0,+1
2 peaks at -1,+1
Correct operation: “+”;Side peaks: FEE mis-configuration
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PHOS offline status 17
Shower shape
15.11.2010
LHC10e: photons Pt>1 GeV/c, contributing to p0 peakl0 = 2.0±0.01s0 = 0.71±0.01l1 = 1.22±0.01s1 = 0.42±0.01c = -0.59±0.03
MC: simple photons
Position of lambda bump is ~10% higher than in MC, width is same.=> Result of decalibration.
l1
l0l0l1
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PHOS offline status 18
Purity and efficiency
15.11.2010
Efficiency S/Bg
No Cuts 100% 0.06
Neutral 96% 0.10
Dispersion 75% 0.23
Disp+Neutral 72% 0.32
Runs 130xxx
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PHOS offline status 19
Good run selectionRuns suitable for physics analysis were selected by studying the output histograms of the analysis train (wagon CaloQA):
• Cell multiplicity
• Cell energy spectrum
• Cluster multiplicity
• Cluster mean energy
• Slope of the cluster energy spectrum
• Number of reconstructed 0 per event.
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PHOS offline status 20
QA:Cluster multiplicity and Mean energy
15.11.2010
Ecluster>0.3 GeV Ecluster>0.5 GeV
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PHOS offline status 21
QAEnergy slope and Number 0 of per event
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PHOS offline status 22
Invariant mass: 0 and in pp
15.11.2010
LHC10e pass1: 215M events
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PHOS offline status 23
Tuning MC to reproduce real data
15.11.2010
•Decalibration is imitated by the Gaussian smearing of calibration parameters with =6.5%.•Non-linearity correction was introduced to MC.•All corrections to MC are applied in analysis. MC in mass production run always with ideal (residual) OCDB.
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PHOS offline status 24
peak position and width in pp
Measured mass of 0 and are consistent with PDG values a proof of good energy linearity.
15.11.2010
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Preparation for HI• Keep same thresholds and other parameters
as for pp=>Use same calibration
Possible caveats: too high occupancy and too large clusters
Two more branches were switched off in last 2 months =>revisit BadMap
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PHOS offline status 26
Invariant mass: 0 in Pb-Pb
15.11.2010
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PHOS offline status 27
Simulation status• Simulation of anchor runs is performed with
the PHOS OCDB objects from raw:// - bad channel map and reconstruction parameters. Calibration is taken from residual OCDB, because calibration improves with time, and simulation will not re-run.
• Applying real calibration parameters is passed to analysis.
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PHOS offline status 28
Summary• PHOS calibration is an offline task which requires the full available
statistics.
• Conditions: calibration parameters, bad channel map, HG/LG ration are stable. Once they are found, then can be used in pass1 reconstruction for future LHC periods.
• Further improvement of PHOS calibration requires 109 pp events. Until this statistics is accumulated, pass1 and pass2 reconstructions have equally good quality.
• Dispersion: Still 10% difference between data and MC – investigating
• Track matching: Accuracy is sufficient for PID cuts. In f direction matching can be improved by modifying “distance” to PHOS for hadrons
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PHOS offline status 29
Backup
15.11.2010
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PHOS offline status 30
Track Matching, LHC10e pass1 dz vs z
Big jumps between + and – z. Within constant sign regions slope consistent with zero.Average offsets: Module 2: -1.3 cm; Module 3: -1.15 cm; Module 4: -0.7 cm. Consistent with LHC10c pass2
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PHOS offline status 31
Track Matching, LHC10e pass1, phi
15.11.2010
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PHOS offline status 32
MC LHC10d4: Hadrons, dz(z)
Slope ~0.2% =>dR~0.9 cm. Should be attributed to the deeper hadron shower than photon.15.11.2010
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PHOS offline status 33
MC LHC10d4: hadrons, phi
15.11.2010