Online Track Reconstruction in the CBM Experiment

1. 1. Segments 2. Counters 1 2 4 3 4. Tracks 3. Track Candidates B C M Track Reconstruction • Cellular Automaton (CA) based track finder algorithm • Kalman filter track fit • Highly optimized code • Single precision calculations • Magnetic field approximation • Reconstruction in several iterations • Highly parallelized code • Data level (SIMD instructions, 4 single-precision floating point calculations in parallel) • Task level (ITBB, parallelization between cores) Cellular Automaton: Build short track segments Connect according to the track model Tree structures appear, collect segments into track candidates Select the best track candidates • Cellular Automaton advantages: • Local w.r.t. data • Intrinsically parallel • Extremely simple • Very fast • Perfect for many-core CPU/GPU Track Reconstruction Efficiency Au+Au central events at 25 AGeV, 8 STS and 2 MVD stations. Efficiency and ratios, % Reference set 97.8 All set 87.6 Clone 0.8 Ghost 12.8 Tracks/ev 733 Time/ev, s 1.4 Reconstructable track: Number of consecutive MC points ≥ 4 All set: p ≥ 0.1 GeV/c Reference set: p ≥ 1 GeV/c Ghost: purity < 70% Computer with two Xeon X5550 processors at 2.7 GHz and 8 MB L3, 1 core is used. Online Track Reconstruction in the CBM Experiment I. Kisel, I. Kulakov, I. Rostovtseva, M. Zyzak (for the CBM Collaboration) E-mail: M.Zyzak@gsi.de Deutsche Physikalische Gesellschaft e.V. Münster 11 0. Hits Tracking Challenge Detector layers Hits • Fixed-target heavy-ion experiment • 107 collisions/s • 1000 charged particles/collision • Non-homogeneous magnetic field • Track reconstruction and displaced vertex search required in the first trigger level Track Finder w.r.t. Detector Inefficiency Au+Au central events at 25 AGeV, 8 STS stations. • The algorithm is stable • Slight efficiency degradation with detector efficiency decreasing • Resolution of track parameters becomes slightly worse because of the smaller number of hits Deterministic Annealing Filter1 Scalability of the Track Finder Task: reduce an influence of attached distorted or noise hits on the reconstructed track parameters. • A weight is introduced to each hit • Algorithm is iterative • With each iteration estimation of the hits weight is improved • Based on SIMD KF track fit benchmark2 Will be further investigated within the CA track finder. Percentage of rejected hits depending on the distance from the shifted hit on the 4th STS station to its Monte-Carlo position has been measured. 1 R. Frühwirth and A. Strandlie, Track Fitting with ambiguities and noise: a study of elastic tracking and nonlinear filters. Comp. Phys. Comm. 120 (1999) 197-214. 2 S. Gorbunov, U. Kebschull, I. Kisel, V. Lindenstruth and W.F.J. Müller, Fast SIMDized Kalman filter based track fit, Comp. Phys. Comm. 178 (2008) 374-383 2 CPUs Intel X5550, 4 cores per CPU, HT,2.7 GHz 4 CPUs AMD E6164HE, 12 cores per CPU,1.7 GHz (in collaboration with Julien Leduc/CERN openlab) Strong many-core scalability for large groups of minimum bias events is observed. 4D Reconstruction for the CBM Experiment Conclusions • For track finding a CA based algorithm is used. • The algorithm is fast and efficient. • The algorithm is robust with respect to the detector inefficiency. • The algorithm shows strong many-core scalability. • The investigation of 4D reconstruction has been started. First idealized 4D STS reconstruction with CA track finder has been investigated. Discrete time have been used. • CBM will have: • Free streaming data • 4D measurements (x, y, z, t) • Track reconstruction prior event recognition • The same efficiency • Slight increase of the processing time with larger size of the time slices