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Track Reconstruction in the STAR TPC with a Cellular Automaton Based Approach

Track Reconstruction in the STAR TPC with a Cellular Automaton Based Approach. Y. Fisyak 1 , I. Kisel 2 , I. Kulakov 2 , J. Lauret 1 , M. Zyzak 2 1 BNL, Brookhaven, USA; 2 GSI, Darmstadt, Germany. CHEP-2010 Taipei, October 18-22, 2010. STAR Experiment at BNL.

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Track Reconstruction in the STAR TPC with a Cellular Automaton Based Approach

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  1. Track Reconstruction in the STAR TPC with a Cellular Automaton Based Approach Y. Fisyak1, I. Kisel2, I. Kulakov2, J. Lauret1, M. Zyzak2 1BNL, Brookhaven, USA; 2GSI, Darmstadt, Germany CHEP-2010 Taipei, October 18-22, 2010

  2. STAR Experiment at BNL • Collider experiment at RHIC, BNL • Up to 200 AGeV Au-Au collisions • Main detector – TPC • Increased RIHC luminosity • New HFT detector (2014) • Upgrade the reconstruction algorithms for: • vectorization • multi-threading • many-core systems CA in STAR

  3. Vector Classes (Vc) Vectorclassesoverload scalar C operators with SIMD/SIMT extensions SIMD Scalar c = a+b vc = _mm_add_ps(va,vb) • Vector classes: • provide full functionality for all platforms • support the conditional operators • phi(phi<0)+=360; • Vc increase the speed by the factor: • SSE2 – SSE4 4x • future CPUs 8x • MICA/Larrabee16x • NVIDIA Fermi research Vector classes enable easy vectorization of complex algorithms M. Kretz, Uni-Frankfurt/FIAS CA in STAR

  4. Cellular Automaton (CA) Track Finder Algorithm in STAR TPC • Reconstruction of track segments in each TPC sector: • Find and link neighbors hits • Clean links • Create segments by fitting chains and adding outer hits • Refit tracks and add inner hits • Selection of tracks • Merge sector tracks into TPC global tracks. a) d) e) c) b) Based on the ALICE HLT TPC CA Track Finder CA in STAR

  5. CA Tracker Front view Side view CA in STAR

  6. CA Tracker: p-p Event with 19 Tracks Front view Side view CA in STAR

  7. CA Tracker: Au-Au Event with 1446 Tracks Front view Side view CA in STAR

  8. Charged Tracks Reconstruction Procedure (CA+Sti) • Reconstruction of track segments in each TPC sector: • Find and link neighbors hits • Clean links • Create segments by fitting chains and adding outer hits • Refit tracks and add inner hits • Selection of tracks • Merge sector tracks into TPC global tracks. • Refit the global tracks with the STAR baseline reconstruction (Sti) with accounting other detectors and all dead materials. • Run Sti with hits left. This recovers ~2% tracks. • Fit primary vertex/vertices. • Fit primary tracks. CA in STAR

  9. Comparison Baseline Reconstruction (Sti) with CA Tracking (CA+Sti) Real Au-Au 200 GeV/n data. CPU time per event Sti tracker CA+Sti tracker Sti tracker CA+Sti tracker global CA tracker sector CA tracker Efficiency for global tracks has been increased on 7-9% CA+Sti is ~50% faster than Sti alone CA track seed finder takes ~10% of the all event reconstruction time CA in STAR

  10. Conclusions • The TPC Cellular Automaton (CA) track finder works within the STAR reconstruction framework as seed finder. • Efficiencies with the CA track finder (CA+Sti) are higher by ~3% for primary tracks and ~9% for global ones, respectively, than for Sti alone. • The efficiency with the CA track finder (CA+Sti) is stable with respect to higher track multiplicities. • Reconstructed track parameters are practically the same (CA+Sti tracks contain slightly more hits than Sti ones). • CA+Sti is ~50% faster than Sti alone. For very high occupancy events CA+Sti speeds up reconstruction by factor of ~10. • The TPC CA track finder takes only ~10% of the whole event reconstruction time. • The TPC CA track finder has been moved to the official repository. • The test production with high statistics is planned for a more accurate tracking comparison and physics evaluation in order to make CA+Sti as baseline tracker and to use it for this year (Run X) data production. • There are possibilities for further speedups of the TPC CA track finder algorithm. • TPC CA track finder will be evaluated in order to use it in the STAR High Level Trigger. CA in STAR

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