1. Status of global tracking and plans for Run2 (for TPC related tasks see Marian’s presentation) 1 R.Shahoyan, 19/03/14

2. 2 Global alignment/calibration framework  Need to realign the detectors before Run2 o SPD filters drilling affects ITS alignment o new SPD modules will appear o Current TRD alignment is not satisfactory  Currently ITS and TPC are aligned internally, then they are aligned globally one with respect to other  Outer detectors alignment is relying on TPC tracks, w/o any feedback on TPC alignment calibration Better constraint would be imposed by the global alignment/calibration  Use Millepede algorithm for simultaneous refitting of detector’s alignment/calibration parameters and tracks (already used for ITS and Muon alignment). The task is planned since > 1 year, but no much progress due to the other priorities  Principal problem to solve: track model for the alignment: Millepede needs derivatives of residuals vs track parameters AND global cov. matrix – not provided by the Kalman  Need to evaluate 2 different approaches: o Using Kalman + smoother (LHCb): mathematically difficult in ALICE (rotations between tracking frames) o Global fit with explicit scattering kinks (ATLAS): numerically expensive Steering Millepede minimization ESD+Friends (or filtered TrackPoints) ITS TPC TRD TOF … parameters to optimize tracks, clusters residuals + their derivatives geometry OCDB Detector-specific units Derived from template class Declare DOFs and calculates track- cluster residuals wrt these DOFs

3. 3 Including the TRD in the tracking (RefitInward)  Gain: factor ~ 2 improvement in the p T resolution  Currently prevented by insufficient alignment of TRD (depend on the global alignment task)  Need to improve TRD tracklet fit (outlier clusters): in the current MC to see improvement in p T resolution we need to apply a cut on TRD χ 2, which kills 30-40% of TRD matches  Uniformity problem: even with complete TRD ~30% of tracks will not be matched → keep copy of tracks with and w/o TRD in the refit? (will require repeating the TPC and ITS RefitInward step twice)  Attempt to use TRD in tracking with current data is in progress (with standalone TRD alignment) https://alice.its.cern.ch/jira/browse/PWGPP-1... PWGPP-8 https://alice.its.cern.ch/jira/browse/PWGPP-1 MC anchored to LHC13b

4. Finalization/validation of HLT seeded offline TPC reconstruction  Need to add to HLT output the track->cluster associations  Consider different options: o If the HLT track finding is reliable (lost cluster, fake clusters), consider only track refit in the offline instead of seeding + afterburner for tracks not found in HLT o If HLT track finding is efficient at low pt, consider:  cluster reduction foreseen for Run3: only clusters attached to HLT tracks are stored (and in tracks’ proximity if the cluster attachment efficiency/purity is not good enough)  store HLT tracks/clusters within certain Z range from IP ; Z, p T ranges need to tuned to preserve tracks for loopers, cosmics tracks, some sample of events unbiased by trigger In Run2 the TPC cluster data will be dominated by the pile-up → suppressing unnecessary tracks/clusters will lead to huge gain in raw data size, CPU speed and memory footprint  Update from Sergey in the end of March – beginning of April 4 Sergey, PWGPP-trk, 02/05/2013

5. 5 Standalone ITS reconstruction in the HLT  Not really global tracking but should be done in Run2 (“consolidation meeting, 14/03/14, https://indico.cern.ch/event/307253/) for: o TPC drift speed calibration (statistics → CPU speed is not an issue) o Vertexing with tracks for Luminous Region measurement with ~ 1 minute periodicity: statistics/efficiency at pT>0.5 GeV is important but this task can be performed also by TPC/ITS tracks in HLT if the drift speed calibration is reliable  Rely on SPD + SSD points (+ vertex constraint, since secondaries reconstruction is irrelevant)  Default plan is that the CA tracker will be adapted to SPD+SSD by I.Kisel group (as prototype for Run3 main ITS tracker). First version was pledged for May 2014 but no reassuring news yet. PhD studen (M.Puccio) spent 2 weeks in GSI to start development of the tracker.  Alternative (proposed by Sergey at yesterday HLT training): use tracklets from current HLT SPD vertex finder as seeds to be completed by SSD points. o Not very large efforts to develop o Worth to have it as a backup solution in case the CA tracker is not fully operational by the end of the year

6. 6 Reduction of reconstruction memory footprint, disk output Requires routine (periodic) optimization. Trying more economic base track parameterization. For the TPC: https://indico.cern.ch/event/302336/contribution/1/material/slides/1.pdf (Marian, Mikolaj) https://indico.cern.ch/event/302336/contribution/1/material/slides/1.pdf Setting up the system for routine validation of simulation/reconstruction Check quality of new releases/tags using standard set of data Started by Marian and Mikolaj… ITS-SA seeded reconstruction of low-p T short tracks in TPC TPC standalone tracking imposes certain requirements on the track length and seed points Low p T tracks (for pions: 100-150 MeV) are seen only in the IROC (looping) May require merging of the loop segments More relevant for Run3, where ITS will lack the PID, hence it is important to decrease as much as possible the TPC p T threshold.