1. Marian Ivanov
TPC status report

2. Outlook - Status of planning - Status of QA
- Validations procedures for central reco
- General readiness of the detector
- Status of calibration and alignment – On Thursday

3. Planning tool Simulation/raw data QA
Usage and implementation of the ALTRO data
Not yet in (Christian, Marek)‏ QA
Work in progress - Peter Christiansen

4. Planning tool/Qa tasks
Recent update - revision: task 2475 should be closed
Comparison of the data with reference data – visualization of the trends of derived variables
See presentation of Jens Wiechula

5. Status of hardware – Dead channels
Calibration data QA and status data written to the OCDB
Long term stability of OCDB entries is monitored
As function of time *guiTime application

6. Status of hardware – Dead channels
And as function of geometry ( TPC calibViewer aplication)‏

7. Validations procedures for central reco
TPC calibration (using reconstructed tracks)‏
Monitoring of the residual calibration
Drift velocity, Gain, Detector matching
Validation train
Detector efficiency/track parameters matching
Primary vertex position/resolution monitoring
Cosmic tracks matching monitoring

9. Minimum calibration
2) we would like to know what minimum calibration is needed to make use of the data for first physics, without waiting for the full machinery. Are there ad-hoc calibration procedures that could be applied quickly in order to start the reconstruction (for instance in the TPC calibrate the effective shift in Z using the data itself, run per run, etc.)

10. ExB effect Original effect ~ 7 mm
Correction checked in 2008 data position restored with precission ~300 microns
Second order correction needed because of radial distortion
Software problem at the beginning of september – B field changed the respresentation - ExB correction not adjusted in correspondance (fixed in the next AliRoot release)‏

11. Alignment Sector missalignemnt about 150 microns
Important factor – tilting of the TPC ~ 1 mm on C side
Misalingment generates the non linerar radial distortion about 2 times bigger than original misalignment
Data analyzed - voltage scans and mechanical scan
Analysis still ongoing

12. Measurement of the longitudinal coordinate of TPC tracks
zi = vdi(t)  ( ti - T0s(t) - t0i(t) )‏
zi  coordinate in longitudinal direction
vdi  drift velocity for ith pad
ti  arrival time of charge cluster
T0s(t)  trigger latency for the sth trigger source (different for different trigger sources and currently not constant in time)‏
t0i  relative time offset for ith pad
vd and t0 have to be calibrated on a pad by pad basis as function of time (minutes level)‏
T0s values have to be know on a run-by- run basis
gas volume with E & B fields B
electron drift
zi = f(ti)‏ y E x z
charged
track
wire chamber
to detect projected tracks
Luciano Musa

13. t0i (relative time offset for ith pad)‏
Online Calibration – calibration parameters and sources of information (1/2)‏
t0i (relative time offset for ith pad)‏
Laser events
Processed by online DA (CE DA) - no track reconstruction
Currently standalone calibration runs
Baseline mode for physics run (laser interleaved with physics events) under commissioning
Calibration Pulser events
Online DA (Pulser DA)‏
Presently daily calibration runs
T0s (trigger latency for the sth trigger source)
CTP information (relative offsets of different trigger sources)
Stored in the OCDB (raw information available since middle Oct). Additional interface still needed (discussion with Trigger group ongoing)‏
Offline validation to be performed
Luciano Musa

14. Vdi (drift velocity for ith pad)‏
Online Calibration – calibration parameters and sources of information (2/2)‏
Vdi (drift velocity for ith pad)‏
Depends on gas density (temperature and pressure) and composition
The TPC temperature map (72 sensors) and cavern pressure (2 sensors) are stored in the OCDB and are essential ingredients for the drift velocity corrections
vd is derived from the arrival time of the signals produced by the laser light impinging the TPC central electrode (CE)
Vd = TPC drift length / (ti(CE) – T0S - t0i)
This method provides a relative accuracy of 0.5  10-4
The absolute accuracy is dominated by T0s (~10-3)‏
A direct and accurate measurement of vd requires the reconstruction of laser tracks (presently not available online)‏
there are plans to reconstruct laser tracks in the HLT
Note: the results of the offline calibration indicate that, due to the variations of the
gas composition, in order to achieve the required drift velocity precision, the laser
has to be ran every 30m
Luciano Musa

15. Offline calibration (after first pass reconstruction)‏
After first pass reconstruction, a more refined and accurate drift velocity calibration can be attained by using the reconstructed tracks
laser events
track matching (valid both for cosmics and beam events)‏
TPC (drift volume A-side) – TPC (drift volume C-side)‏
TPC – ITS
Offline we achieve a relative accuracy of 210-5
Luciano Musa

16. Status
Preamble - The validation (accuracy and stability) of the drift velocity calibration
has been a complex and lengthy task
optimization of laser and pulser operation
optimization of online algorithms (DAs)
test over a long period of time (many weeks)‏
test and optimization of the offline algorithms, based on track reconstruction
and of the overall TPC calibration
Status
All calibration functions and OCDB entries that are needed to reprocess the old data (from July to mid October) are validated (after first pass reconstruction) and committed to the ALIROOT development repository (trunk)‏
A few additional calibration functions, which are needed for the proper reconstruction of
new data, need validation next week
correction of T & laser run
user interface function for trigger offsets
correction for trigger offsets
Luciano Musa