PHOS offline status report

1. ALICE offline week, 15.11.2010 PHOS offline status report Dmitri Peressounko

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. 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. 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 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 passes PHOS offline status

6. Calibration with <E> • Foreach PHOS cellcalculatemeanenergy <Ei> in the range E>0.06 GeV • Calculatecorrectionstothe CC: • Ci= const/<Ei>, whereconstwas adjusted to putπ0peakto135 MeV/c2. • UseCitocalculate <Ei> ofthenextiteration: • recalibratecellenergywithCi • recalculateenergyandpositionofthecluster • Calibration was found on 70M event sample PHOS offline status

7. Module 4 before calibration PHOS offline status

8. Module 4 after calibration 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. PHOS offline status

10. HG/LG measurements • HG/LG ratio varies within RMS 2%. • Mean value is different in module 4 compared with modules 2 and 3. PHOS offline status

11. Bad channel map • 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 three Pedestal+Quality Quality+Noise Quality Pedestal Noise PHOS offline status

12. Track Matching, LHC10c pass2 dzvs 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?) 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 PHOS offline status

14. Timing: Pileup Runs analyzed (LHC10e): 130795,130799,130802,130803,130834,130842,130844,130848,130850 Pileup: Wrong bands disappear if PhysicsSelection +Zvtx cut applyed PHOS performance in pp

15. Timing: L1phase shift Subtracting: EMCAL/TPC Adding: PHOS PHOS performance in pp

16. 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

17. Shower shape l0 l0 l1 MC: simple photons l1 LHC10e: photons Pt>1 GeV/c, contributing to p0 peak l0 = 2.0±0.01 s0 = 0.71±0.01 l1 = 1.22±0.01 s1 = 0.42±0.01 c = -0.59±0.03 Position of lambda bump is ~10% higher than in MC, width is same. => Result of decalibration. PHOS offline status

18. Purity and efficiency Runs 130xxx PHOS offline status

19. Good run selection Runs 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. PHOS offline status

20. QA:Cluster multiplicity and Mean energy Ecluster>0.3 GeV Ecluster>0.5 GeV PHOS offline status

21. QAEnergy slope and Number 0 of per event PHOS offline status

22. Invariant mass: 0 and  in pp LHC10e pass1: 215M events PHOS offline status

23. Tuning MC to reproduce real data • 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. 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. PHOS offline status

25. 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

26. Invariant mass: 0in Pb-Pb 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. 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 PHOS offline status

29. Backup PHOS offline status

30. Track Matching, LHC10e pass1 dzvs 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 PHOS offline status

31. Track Matching, LHC10e pass1, phi 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. PHOS offline status

33. MC LHC10d4: hadrons, phi PHOS offline status