Akishina, V.

Kisel, I.

Kulakov, I.

Zyzak, M.

GSI Repository

The Cellular Automaton track finder at high track multiplicities for CBM∗V. Akishina1,2,3, I. Kisel1,2,4, I. Kulakov1,2,4, and M. Zyzak1,2,41Uni-Frankfurt, Germany; 2GSI, Darmstadt, Germany; 3JINR, Dubna, Russia; 4FIAS, Frankfurt am Main, GermanyThe CBM experiment at FAIR is being designed to studyheavy-ion collisions at extremely high interaction rates (upto 10 MHz) and high track multiplicities (up to 1000).Since the beam in the CBM experiment will have no bunchstructure, but continuous, the groups of events may be closeor overlapped in time. Measurements in this case will be4D (x, y, z, t). Thus, the reconstruction of time slices ratherthan events will be needed. In addition to such high inputrate and complicated event topology, the full event recon-struction and selection will be done at the First Level EvenSelection (FLES) stage. In this respect, both the speed ofthe reconstruction algorithms and their efficiency are cru-cial.The Cellular Automaton (CA) [1] track finder is fast androbust and thereby is used both for the online and offlinetrack reconstruction in the CBM experiment. The algo-rithm creates short track segments in each three neighbour-ing stations, then combines them into track-candidates andselects the best tracks according to the maximum lengthand minimum χ2 criteria. The algorithm was further opti-mized for the case of high track multiplicity with respectto time: additional sorting of found hits according to 2-dimensional (y, z) grid was introduced in order to speedup the search for the next hit. The standalone FLES pack-Figure 1: Reconstructed tracks in minimum bias event(left) and packed group of 100 minimum bias events (right),109 and 10 340 tracks in average respectively.age [2] was used to investigate the stability of the CA trackreconstruction with respect to a track multiplicity per event.For the study 1000 of minimun bias Au+Au UrQMD eventsat 25 AGeV was simulated. As the first step towards 4Dtracking a number of minimum bias events (up to 100) werepacked into one group with no time measurement taken intoaccount. The group was treated by the CA track finder as a∗This work was supported by the Hessian LOEWE initiative throughthe Helmholtz International Center for FAIR (HIC for FAIR) and EU-FP7 HadronPhysics2. Das Projekt wird vom Hessischen Ministerium fuerWissenschaft und Kunst gefoerdert.single event and the regular reconstruction procedure wasperformed (Figure 1).The dependence of the track reconstruction efficiencyon the track multiplicity is stable (Figure 2). In particu-lar, the efficiency of the algorithm decreases only by 4%for 100 minimum bias events in one group, comparing tothe case of a single minimum bias event. The efficien-cies for the reference tracks (p > 1 GeV/c), which in-clude tracks of particular physics interest, remains high forall range of track multiplicities. The efficiencies for extra(100 MeV/c < p < 1 GeV/c) and secondary tracksare also stable. The level of ghost tracks is less than 10%.Thus, the study has shown that the CA track finder is stableFigure 2: Track reconstruction efficiencies and ghost ratefor different sets of tracks versus track multiplicity.with respect to the track multiplicity.The speed of the algorithm was studied as a function oftrack multiplicity. The time, which algorithm needs to pro-ceed a grouped event, behaves as a second order polyno-mial with respect to a number events in the group. Dueto this fact, the CA track finder needs less than 2 secondsin order to reconstruct a grouped event combined of 100minimum bias events, that corresponds to about 10 000 re-constructed tracks.Summarizing, the CA track finder reconstruction algo-rithm shows high speed performance and stability with re-spect to the track multiplicities, up to the extreme case ofabout 10 000 reconstructed tracks per event.References[1] I. Kisel, Nucl. Instr. and Meth. A566 (2006) 85-88.[2] V. Akishina, I. Kisel, I. Kulakov, M. Zyzak, FLES: Stan-dalone First Level Event Selection Package for the CBM ex-periment, this report.PHN-NQM-EXP-48 GSI SCIENTIFIC REPORT 201278

The Cellular Automaton track finder at high track multiplicities for CBM

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The Cellular Automaton track finder at high track multiplicities for CBM

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