Marian Ivanov TPC status report

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

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

Planning tool/Qa tasks Recent update - revision: 36017 0 - task 2475 should be closed Comparison of the data with reference data – visualization of the trends of derived variables See presentation of Jens Wiechula

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

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

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

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.)

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)‏

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

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

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

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

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

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 & P @ laser run user interface function for trigger offsets correction for trigger offsets Luciano Musa