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PHOS offline status reportDmitri PeressounkoALICE offline week, 15.11.2010Reconstruction statusRaw 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.15.11.2010PHOS offline status2Online DQMPHOS 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.15.11.2010PHOS offline status3PHOS OCDB objectsEnergy calibration: conversion from ADC counts to GeVHigh gain/low gain ratioBad channel mapAlignmentReconstruction parametersAll objects are produced offline15.11.2010PHOS offline status4PHOS energy calibrationPre-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 calibrationLHC10c: pass1 raw calibration, pass2 latest calibrationLHC10d: pass1 was corrupted due to OCDB error cant be used, pass 2 OKLHC10f, g: latest calibration in both passes15.11.20105PHOS offline statusCalibration with 15.11.2010PHOS offline status6For each PHOS cell calculate mean energy in the range E>0.06 GeVCalculate corrections to the CC:Ci = const/, where const was adjusted to put 0 peak to 135 MeV/c2.Use Ci to calculate of the next iteration:recalibrate cell energy with Cirecalculate energy and position of the clusterCalibration was found on 70M event sample6Module 4 before calibration15.11.2010PHOS offline status7

Module 4 after calibration15.11.2010PHOS offline status8

PHOS HG/LG calibrationPHOS FEE measures energy by 2 ADCs with different gains:High gain: 2 MeV 2 GeV, 10 bitsLow gain: 32 MeV 32 GeV, 10 bitsRatio 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 GeVHG/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.15.11.20109PHOS offline statusHG/LG measurements15.11.2010PHOS offline status10

HG/LG ratio varies within RMS 2%.Mean value is different in module 4 compared with modules 2 and 3.

Bad channel map15.11.2010PHOS offline status11

Bad channel map was found off-line from different sources of information:Pedestal runsLED runs with variable amplitudeLED runs with zero amplitudePhysics runsIn total 1371 channels are bad (out of 10752)All threePedestal+QualityQuality+NoiseQualityPedestalNoise

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?)15.11.201012PHOS offline statusTrack 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 15.11.201013PHOS offline statusTiming: Pileup8.11.2010PHOS performance in pp14

Runs analyzed (LHC10e): 130795,130799,130802,130803,130834,130842,130844,130848,130850Wrong bands disappear if PhysicsSelection +Zvtx cut applyedPileup:Timing: L1phase shift8.11.2010PHOS performance in pp15

Subtracting:EMCAL/TPCAdding:PHOSTiming: L1phase shift - Side peaks

Single peak at 0Single peak at -1Single peak at +12 peaks at -1,02 peaks at 0,+12 peaks at -1,+1

Correct operation: +;Side peaks: FEE mis-configurationShower shape15.11.2010PHOS offline status17

LHC10e: photons Pt>1 GeV/c, contributing to p0 peak

l0 = 2.00.01s0 = 0.710.01l1 = 1.220.01s1 = 0.420.01c = -0.590.03

MC: simple photonsPosition of lambda bump is ~10% higher than in MC, width is same.=> Result of decalibration.l1l0

l0l1Purity and efficiency15.11.2010PHOS offline status18EfficiencyS/BgNo Cuts100%0.06Neutral96%0.10Dispersion75%0.23Disp+Neutral72%0.32

Runs 130xxxGood run selectionRuns suitable for physics analysis were selected by studying the output histograms of the analysis train (wagon CaloQA):Cell multiplicityCell energy spectrumCluster multiplicityCluster mean energySlope of the cluster energy spectrumNumber of reconstructed 0 per event.15.11.2010PHOS offline status19QA:Cluster multiplicity and Mean energy15.11.2010PHOS offline status20

Ecluster>0.3 GeVEcluster>0.5 GeVQAEnergy slope and Number 0 of per event15.11.2010PHOS offline status21

Invariant mass: 0 and in pp15.11.201022PHOS offline status

LHC10e pass1: 215M eventsTuning MC to reproduce real data15.11.2010PHOS offline status23

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.

peak position and width in ppMeasured mass of 0 and are consistent with PDG values a proof of good energy linearity.15.11.201024PHOS offline statusPreparation for HIKeep 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 BadMapInvariant mass: 0 in Pb-Pb15.11.2010PHOS offline status26

Simulation statusSimulation 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.15.11.2010PHOS offline status27SummaryPHOS 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 investigatingTrack matching: Accuracy is sufficient for PID cuts. In f direction matching can be improved by modifying distance to PHOS for hadrons15.11.2010PHOS offline status28Backup15.11.2010PHOS offline status29Track 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 pass215.11.201030PHOS offline statusTrack Matching, LHC10e pass1, phi

15.11.201031PHOS offline statusMC LHC10d4: Hadrons, dz(z)

Slope ~0.2% =>dR~0.9 cm. Should be attributed to the deeper hadron shower than photon.15.11.201032PHOS offline statusMC LHC10d4: hadrons, phi

15.11.201033PHOS offline status