ALICE offline week 15 11 2010 PHOS offline

ALICE offline week, 15. 11. 2010 PHOS offline status report Dmitri Peressounko

Reconstruction status • Raw data reconstruction: – Fast fitting with Gamma. N is implemented. No much improvement neither in Amp, no by using c 2 cut => do not use. – Correction for a time stamp by the L 1 phase read out of ALTRO trailer. • Time gate was introduced to Reco. Parameters 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. 2010 PHOS offline status 2

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. 15. 11. 2010 PHOS offline status 3

PHOS OCDB objects • Energy calibration: conversion from ADC counts to Ge. V • High gain/low gain ratio • Bad channel map • Alignment • Reconstruction parameters • All objects are produced offline 15. 11. 2010 PHOS offline status 4

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 pass 1 and pass 2 reconstructions for PHOS: – LHC 10 b: pass 1, pass 2 – both initial calibration – LHC 10 c: pass 1 – raw calibration, pass 2 – latest calibration – LHC 10 d: pass 1 was corrupted due to OCDB error can’t be used, pass 2 OK – LHC 10 f, g: latest calibration in both passes 15. 11. 2010 PHOS offline status 5

Calibration with <E> For each PHOS cell calculate mean energy <Ei> in the range E>0. 06 Ge. V Calculate corrections to the CC: Use Ci to calculate <Ei> of the next iteration: Ci = const/<Ei>, where const was adjusted to put π0 peak to 135 Me. V/c 2. recalibrate cell energy with Ci recalculate energy and position of the cluster Calibration was found on 70 M event sample 15. 11. 2010 PHOS offline status 6

Module 4 before calibration 15. 11. 2010 PHOS offline status 7

Module 4 after calibration 15. 11. 2010 PHOS offline status 8

PHOS HG/LG calibration • PHOS FEE measures energy by 2 ADCs with different gains: • High gain: 2 Me. V – 2 Ge. V, 10 bits • Low gain: 32 Me. V – 32 Ge. V, 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 Me. V – 32 Ge. V • 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. 15. 11. 2010 PHOS offline status 9

HG/LG measurements • HG/LG ratio varies within RMS 2%. • Mean value is different in module 4 compared with modules 2 and 3. 15. 11. 2010 PHOS offline status 10

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) 15. 11. 2010 PHOS offline status All three Pedestal+Quality+Noise Quality Pedestal Noise 11

Track Matching, LHC 10 c pass 2 dz vs z No slope in dz(z) distribution. Still there is some jump between + and – z: 0. 3315. 11. 2010 cm for mod. 3 and 0. 2 cm for mod 4. PHOS (residual TPC decalibration + TPC sector dependence? ) offline status 12

Track Matching, LHC 10 c pass 2, phi No unique slope for all distributions. 15. 11. 2010 PHOS Overall offsets: Module 2: -0. 7 cm; Module 3: offline -0. 8 status cm; Module 4: -0. 9 cm 13

Timing: Pileup Runs analyzed (LHC 10 e): 130795, 130799, 130802, 13 0803, 130834, 130842, 1308 44, 130848, 130850 Pileup: Wrong bands disappear if Physics. Selection +Zvtx cut applyed 8. 11. 2010 PHOS performance in pp 14

Timing: L 1 phase shift Subtracting: EMCAL/TPC Adding: PHOS 8. 11. 2010 PHOS performance in pp 15

Timing: L 1 phase 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

Shower shape l 0 l 1 l 0 MC: simple photons l 1 LHC 10 e: photons Pt>1 Ge. V/c, contributing to 0 peak l 0 = 2. 0± 0. 01 0 = 0. 71± 0. 01 l 1 = 1. 22± 0. 01 1 = 0. 42± 0. 01 c = -0. 59± 0. 03 15. 11. 2010 Position of lambda bump is ~10% higher than in MC, width is same. => Result of decalibration. PHOS offline status 17

Purity and efficiency Runs 130 xxx 15. 11. 2010 Efficiency S/Bg No Cuts 100% 0. 06 Neutral 96% 0. 10 Dispersion 75% 0. 23 Disp+Neutral 72% 0. 32 PHOS offline status 18

Good run selection Runs suitable for physics analysis were selected by studying the output histograms of the analysis train (wagon Calo. QA): • Cell multiplicity • Cell energy spectrum • Cluster multiplicity • Cluster mean energy • Slope of the cluster energy spectrum • Number of reconstructed 0 per event. 15. 11. 2010 PHOS offline status 19

QA: Cluster multiplicity and Mean energy Ecluster>0. 3 Ge. V 15. 11. 2010 Ecluster>0. 5 Ge. V PHOS offline status 20

QA Energy slope and Number 0 of per event 15. 11. 2010 PHOS offline status 21

Invariant mass: 0 and in pp LHC 10 e pass 1: 215 M events 15. 11. 2010 PHOS offline status 22

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. 15. 11. 2010 PHOS offline status 23

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 PHOS offline status 24

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 Bad. Map

Invariant mass: 0 in Pb-Pb 15. 11. 2010 PHOS offline status 26

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. 15. 11. 2010 PHOS offline status 27

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 pass 1 reconstruction for future LHC periods. • Further improvement of PHOS calibration requires 109 pp events. Until this statistics is accumulated, pass 1 and pass 2 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 15. 11. 2010 PHOS offline status 28

Backup 15. 11. 2010 PHOS offline status 29

Track Matching, LHC 10 e pass 1 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: offline -1. 15 cm; Module 4: -0. 7 cm. 15. 11. 2010 PHOS status Consistent with LHC 10 c pass 2 30

Track Matching, LHC 10 e pass 1, phi 15. 11. 2010 PHOS offline status 31

MC LHC 10 d 4: Hadrons, dz(z) Slope ~0. 2% =>d. R~0. 9 cm. Should be attributed the deeper hadron shower than photon. 15. 11. 2010 PHOS offline to status 32

MC LHC 10 d 4: hadrons, phi 15. 11. 2010 PHOS offline status 33