SDD offline status

1. SDD offline status Francesco Prino INFN sezione di Torino ALICE offline week – March 15th 2010

2. Summary of main changes since October 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 simulation • Alignment • Millepede results for Alignment+Calibration • Ongoing cross-checks • QA + Pilot Train

3. Module-by-module ADC->keV • Fit 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

4. Module-by-module ADC->keV • From pass4 with module-by-module ADC calibartion with E. Biolcati

5. Cluster selection • Loss 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 Run 104892 pass 4 Run 104892 pass 2 with A. Dainese

6. SDD efficiency • Effect 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. with A. Dainese Run 104892 pass 2 Data/MC Run 104892 pass 4

7. Injector DA • Drift speed extracted online from injector runs • Use 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 borders • Improved 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

8. Raw data to SDigits • Checking 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)

9. Treatment of gain in simulation • Gain 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 factor • In 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

10. Alignment R. Shahoian • Special 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

11. Alignment: checks (I) R. Shahoian • 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

12. Alignment: checks (II) R. Shahoian • 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 Residuals (cm) Residuals (cm) Black = only survey Red = Millepede alignment+ calib

13. Alignment: on-going and to-do • Drift time distribution at low times under investigation • Peak close to time zero • Due to particles crossing the sensors beyond the anodes • Loss of efficiency • May be due to online zero suppression, being checked • Try to fix TimeZero for half ladders in MillepedeII • Validate 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 residuals

14. Correction maps • Residuals 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 Millepede Xloc Residual (cm) S. Beolè Millepede + Laser map Xloc Residual (cm) Xloc (cm)

15. QA/DQM M. Siciliano • AliITSQASDDDataMakerRec: • 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

16. SDD Task in Pilot Train • Task 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. drift time • Will be improved (with new plots concerning efficiency and extra clusters) in the next days

17. Other ongoing activities • Scan 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 investigation • Cluster 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 anode • Simulation • Checks for the ≈10 modules that have not the same efficiency in data and MC