Status of the HLT TPC tracker Sergey Gorbunov
Status of the HLT TPC tracker Sergey Gorbunov 1 1 Kirchhoff Institute for Physics, University of Heidelberg, Germany CERN, 25. 06. 2009 Sergey Gorbunov, KIP ALICE offline week CERN, June 25, 2009
TPC reconstruction scheme in HLT TPC slice 0 Cluster finder clusters Slice tracker slice tracks The TPC Slice Tracker is the most complicated algorithm: § combinatorial search § fit mathematics the reconstruction time is crucial … … … slice tracks TPC slice 35 Cluster finder clusters Slice tracker slice tracks TPC Global merger TPC tracks CERN, 25. 06. 2009 Sergey Gorbunov, KIP 2/13
The Cellular Automaton tracking for ALICE TPC 1. Neighbours 2. finder n For each TPC cluster find two (up&down) neighbours which compose the best line 2. Composing of tracklets n One-to-one linked neighbours are grouped to the track segments 3. Construction of the track candidates 4. Final selection of tracks n Fit of trajectories n Search for the missed parts n Competition between tracks, no shared clusters allowed CERN, 25. 06. 2009 Sergey Gorbunov, KIP 3/13
HLT tracks on the event display CERN, 25. 06. 2009 Sergey Gorbunov, KIP 4/13
HLT TPC Tracker quality checks (“Ali. HLTTPCComparison. C” macro) - official quality check for HLT ESDs - modification of Ali. TPCComparison. MI. C CERN, 25. 06. 2009 Sergey Gorbunov, KIP 5/13
HLT TPC Tracker performance 99. 94% 99. 86% pp, HLT 9. 06% 9. 30% 0. 19% 0. 21% 98. 15% 95. 84% central Pb. Pb, HLT CERN, 25. 06. 2009 pp, Offline central Pb. Pb, Offline 13. 22% 12. 13% 1. 66% 1. 40% Sergey Gorbunov, KIP 6/13
HLT TPC Tracker performance pp events HLT Tracker : test/ppbench/ Offline Tracker : Time = 66. 0 ms Eff = 99. 94% Ghost = 0. 21% Clone = 9. 30% Time = 19. 6 ms Eff = 99. 86% Ghost = 0. 19% Clone = 9. 06% Central Pb. Pb events test/Pb. Pbbench/* Ali. Gen. Hijing *gener = Hijing. Standard(); gener->Set. Impact. Parameter. Range(0. , 0. ); HLT Tracker : Time = 17. 6 s Eff = 98. 15% Ghost = 1. 66% Clone = 13. 22% CERN, 25. 06. 2009 includes kink finder etc, but no fwd/bck propagation. was better before, some problem in trunk Sergey Gorbunov, KIP Offline Tracker : Time = 160. 1 s Eff = 95. 84% Ghost = 1. 40% Clone = 12. 13% 7/13
HLT TPC Tracker performance cosmic events macros/Config_Ali. Gen. Cosmics. Param. C HLT Tracker : Eff = 100. 0% Ghost = 0. 0% Clone = 50. 1% CERN, 25. 06. 2009 Sergey Gorbunov, KIP Two parts of track 8/13
Resolutions pp CATracker for pp (1000 events): offset Pt, % Y, mm , mrad Z, mm , mrad . 77 0. 42 1. 67 0. 41 0. 94 1. 47 1. 45 0. 97 0. 72 Resolution (+0. 21) Pull 1. 30 Off-line tracker for pp (1000 events): offset CERN, 25. 06. 2009 Pt, % Y, mm , mrad Z, mm , mrad . 74 0. 39 1. 48 0. 44 0. 97 1. 23 1. 22 0. 93 0. 71 Resolution (+0. 21) Pull 1. 29 Sergey Gorbunov, KIP 9/13
Resolutions Pb. Pb CATracker for central Pb. Pb (1 event): Pt, % 1. 19 Resolution (+0. 22) Pull 1. 70 Y, mm , mrad Z, mm , mrad 0. 95 3. 12 0. 91 1. 55 2. 24 2. 35 1. 43 0. 88 Off-line tracker for central Pb. Pb (1 event): Pt, % CERN, 25. 06. 2009 1. 03 Resolution (+0. 23) Pull 1. 53 Y, mm , mrad Z, mm , mrad 0. 72 2. 48 0. 75 1. 35 2. 02 1. 67 1. 41 0. 90 Sergey Gorbunov, KIP 10/13
Use of parallel hardware: GPU devices NVIDIA Ge. Force GTX 280: n 30 x 8 general propose processors; pure calculations can be ~100 times faster than CPU n very parallel: || execution of branches, || memory access n CUDA language - a little extension of C++ n fast access to the small portion of data (16 k) at the time; no memory cache n single precision floating point n ONLY parallel calculations CERN, 25. 06. 2009 Sergey Gorbunov, KIP 11/13
Running the slice tracker on the GPU cluster at Frankfurt University CPU CERN, 25. 06. 2009 • speed-up: 10. 5 x • same code • same result Sergey Gorbunov, KIP GPU 12/13
Summary and plans pp, HLT pp, Offline Status of the HLT TPC tracker : • Ready for pp Plans : • Fit improvement - offsets and pulls • Strategy for deconvolution of TPC clusters for Pb. Pb • Use of parallel hardware for Pb. Pb central Pb. Pb, HLT CERN, 25. 06. 2009 Sergey Gorbunov, KIP central Pb. Pb, Offline 13/13
- Slides: 13