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SDD offline statusSDD offline status

Francesco PrinoINFN sezione di Torino

ALICE offline week – March 15th 2010

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Summary of main changes since Summary of main changes since October 2009October 2009

Module-by-module ADC->keV calibration Modified OCDB objects, calibration constants from p-p 2009 data

Updates in noise rejection in Cluster Finder Improved efficiency for large drift times

Improvements in Injector DA Avoid artifacts of the polynomial fit to drift speed vs. anode

Fixes for signal embedding Few updates needed in the treatment of raw->SDigits conversion

Improved treatment of anode gain in simulationAlignment Millepede results for Alignment+Calibration Ongoing cross-checks

QA + Pilot Train

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Module-by-module ADC->keVModule-by-module ADC->keVFit the p-p dE/dx distributions for each SDD module with a Landau+Gauss 85% of modules have

ADC value within 5% from expected value

AliITSresponseSDD modified to contain 260 SDC->keV conversion factors (1 per module) Committed on Jan

13th 2010 Improved calibration

used since pass4

Layer 3 Layer 4

with E. Biolcati

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Module-by-module ADC->keVModule-by-module ADC->keVFrom pass4 with module-by-module ADC calibartion

with E. Biolcati

Cluster selectionCluster selectionLoss of efficiency observed with increasing drift time in pass2 data Larger loss on layer 3 than on layer 4

Reason for the efficiency loss: SDD clusters removed by the cut on the cluster size applied to remove noise clusters Cluster size increases with increasing drift time due to charge diffusion

The larger loss on layer 3 possibly due to the higher temperature which causes larger charge diffusion Cuts on cluster

size released to recover missing efficiency Committed to

trunk on Feb 3rd 2010

OK in pass 4 reconstruction

Region close to anodes (small drift times, latge |xloc| under investigation

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Run 104892 pass 2 Run 104892 pass 4

with A. Dainese

SDD efficiencySDD efficiencyEffect of the looser cuts on cluster size which allow to recover in pass4 the missing efficiency at large drift times + new objects in OCDB sim (closer to real detector) for simulation Few modules still show discrepancy between data and MC under

investigation.

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Run 104892 pass 2

Run 104892 pass 4

Dat

a/M

C

with A. Dainese

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Injector DAInjector DADrift speed extracted online from injector runsUse a polynomial function to model the vdrift dependence on anode coordinate Need a 3rd degree polynomial Artifacts in the fit for some modules due to missing injectors

on the bordersImproved fit imposing these conditions: Vdrift maximum close to the center of the sensor No other points with derivative = 0

All injector runs from p-p data taking have been reprocessed and improved DriftSpeedSDD objects have been put in OCDB, just before pass5 Allowed also to improve the Millepede alignment

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Raw data to SDigitsRaw data to SDigitsChecking of embedding for ITS showed anomalous results for SDD (M. Poghosyan)Problems due to the fact that the raw->Sdigits conversion method was not updated since long time and did not contain the upgrades applied in the RawStreamSDD decoder in the last year Crash for some events

Due to missing decoding of newly introduced words Anomalous results: missing clusters in the merged event,

wrong cluster coordinates Due to “old-style” treatment of zero suppression threshold and drift side

All problems (mainly in AliITS.cxx) fixed with these two commits: 38956 (Feb 17th) and 39464 (Mar 9th)

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Treatment of gain in simulationTreatment of gain in simulationGain is measured anode-by-anode in PULSER runs and stored in the OCDB in the AliITSCalibrationSDD objects (in CalibSDD) NOTE: CalibSDD used iboth in simulation and reconstruction

In RECONSTRUCTION: the anode gain is “normalized” to the average gain before being used to correct the measured ADC counts Gain correction is meant to equalize the gain among different anodes,

the “absolute” calibration is done with the ADC->keV conversion factorIn SIMULATION the anode gain was applied as it was to the ADC counts Due to the fact that in the ICDB sim the simulated gain had average = 1

by construction, so the normalization to the average gain was not needed

Weak point gave rise to miscalibrated signals when “real” detector parameters were put in OCDB sim

Pass4 simulations had dE/dx off by ≈30% due to this problem (affects only SIM, not DATA) Not a blocking problem: dE/dx can be easily renormalized at the analysis level

Improved treatment of gain in simulation (introducing the normalizaation to the average gain) committed on Feb. 25th

ADC->keV conversion factors in OCDB sim updated accordingly

AlignmentAlignmentSpecial feature for SDD in Millepede II: calibration parameters (TimeZero and drift speed correction) added on top of geometrical misalignments as free parameters in the fit to track-to-point residuals Time Zero initial values estimated from residuals in the two drift

regions , in the future better to use minimum drift time Vdrift correction needed for:

Modules with malfunction injectors ( ≈ 30%) Systematic effects in the estimation of the drift speed with injector

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R. Shahoian

Alignment: checks (I)Alignment: checks (I)Fix modules w.r.t. ladders to the survey measurements and leave free in Millepede: TimeZero and vdrift for each module Rotations and translation for ladders

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R. Shahoian

Alignment: checks (II)Alignment: checks (II)Use run 104892 to extract parameters and compute residuals on run 104321 Run 104321 is “served” by a different DriftSpeedSDD

object, so it can be used to check if the drift speed corrections extracted from one set of runs can be applied to other runs

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R. Shahoian

Black = only surveyRed = Millepede alignment+ calib

Residuals (cm) Residuals (cm)

Alignment: on-going and to-doAlignment: on-going and to-doDrift time distribution at low times under investigation Peak close to time zero

Due to particles crossingthe sensors beyond the anodes

Loss of efficiencyMay be due to online zero

suppression, being checked

Try to fix TimeZero for half ladders in MillepedeIIValidate correction maps and include them in reco For about 10% of the modules significant non-

uniformities of the drift field are present and have been mapped with laser measurements during construction

Should improve significantly the track-to-point residuals13

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Correction mapsCorrection mapsResiduals along drift axis vs. drift coord. from p-p data after Millepede with and without correction based on laser maps Tested on 5 modules with larger effects

GOAL: Validate the correction extracted from laser Promising results, but more checks are needed

Xloc

Res

idua

l (cm

)Xl

oc R

esid

ual (

cm)

Xloc (cm)

Millepede

Millepede + Laser map

S. Beolè

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QA/DQMQA/DQMAliITSQASDDDataMakerRec: ResetDetector added: reset of the histograms and set to

zero of the calibration objects Raws and in the RecPoints lists: added the normalized (to

the number of alive channels taken from OCDB) histograms of the module pattern and of the layer patterns. Histograms set as Expert histograms.

AliITSQASDDChecker: Raw Data: simple checks RecPoints: simple checks (not in the trunk)

AliITSQASDDDataMakerSim: All histograms have been implemented

AliITSQASDDChecker: Check for SIM histos To be implemented

M. Siciliano

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SDD Task in Pilot TrainSDD Task in Pilot TrainTask PWG1/ITS/AliAnalysisTaskSDDRP Included in Pilot Train to check SDD performance in first p-p

data Based on RecPoint+ESD+ESDfriend information Allow to do more detailed checks of performance and

calibration with respect to standard QA E.g. cluster charge corrected

for track inclination vs. drifttime

Will be improved (with new plots concerning efficiency and extra clusters) in the next days

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Other ongoing activitiesOther ongoing activitiesScan of raw data to understand the problem of missing efficiency at low drift times Likely to be due to the zero suppression algorithm, but

needs some further investigationCluster selection in the cluster finder Develop more refined cuts (not only cluster size) to reject

noise clusters Develop a special treatment for clusters on the border or

close to a dead anodeSimulation Checks for the ≈10 modules that have not the same

efficiency in data and MC