PHOS offline status report

Dmitri Peressounko

ALICE offline week, 15.11.2010

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.

15.11.2010

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.

15.11.2010

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

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

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

PHOS offline status 7

Module 4 before calibration

15.11.2010

PHOS offline status 8

Module 4 after calibration

15.11.2010

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.

15.11.2010

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.

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

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

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

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:

PHOS performance in pp 15

Timing: L1phase shift

8.11.2010

Subtracting:EMCAL/TPC

Adding:PHOS

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

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

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

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.

15.11.2010

PHOS offline status 20

QA:Cluster multiplicity and Mean energy

15.11.2010

Ecluster>0.3 GeV Ecluster>0.5 GeV

PHOS offline status 21

QAEnergy slope and Number 0 of per event

15.11.2010

PHOS offline status 22

Invariant mass: 0 and in pp

15.11.2010

LHC10e pass1: 215M events

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.

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

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

PHOS offline status 26

Invariant mass: 0 in Pb-Pb

15.11.2010

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.

15.11.2010

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

15.11.2010

PHOS offline status 29

Backup

15.11.2010

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

15.11.2010

PHOS offline status 31

Track Matching, LHC10e pass1, phi

15.11.2010

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

PHOS offline status 33

MC LHC10d4: hadrons, phi

15.11.2010