Tracking in high-multiplicity events
Tracking in high-multiplicity events
复制标题
跟踪高多样性事件
DOI：
10.22323/1.287.0043
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
M. Puccio
中科院分区：
文献类型：
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作者：
M. Puccio
Alice实验正在准备对其内部硅跟踪器(内部跟踪系统)以及在线和离线系统进行重大升级，以应对即将于2021年开始的大型强子对撞机第三次运行。
在第三次运行期间，大型强子对撞机将在{S{NN}，=5.5$TeV处产生铅-铅碰撞，峰值光度为数学上的{L}，=6倍，相互作用速率为50千赫，与大型强子对撞机目前提供的8千赫的设计相互作用速率相比较。ALICE的目的是为了应对如此高的交互速率，同时提高硅跟踪器的分辨率和效率。在这种情况下，迅速校准外部探测器和加快离线数据处理的要求之一是在升级后的内跟踪系统中在线运行轨道重建。
为了解决这一问题，提出了一种基于元胞自动机的新算法。在该算法中，跟踪被分成多个阶段，以利用数据的局部性。首先，命中点被组织在方位角和纵向坐标的扇区中；然后，该算法独立地在探测器的这些扇区内寻找轨迹段。具有兼容轨道参数的轨道段被标记为相邻的。然后，在最后阶段使用元胞自动机机制定义的一组规则合并相邻的轨迹段，这与Conway的生命游戏中使用的规则集有些类似。
所获得的计算和跟踪性能符合Alice的要求，能够在高径迹密度(直到2000年)的事件中重建出低至100 MeV$/c$的横向动量径迹。在中心铅铅事件为$\Sqrt{S_{NN}}\，=\，5.5$TeV的情况下，该算法的跟踪和计算性能将显示出来。
The ALICE experiment is preparing a major upgrade of its inner silicon tracker (the Inner Tracking System) and of its Online and Offline systems for the upcoming Run3 of the LHC starting in 2021.
During Run3, LHC will deliver Pb-Pb collisions at $\sqrt{s_{NN}}\,=\,5.5$ TeV with a peak luminosity $\mathcal{L}\,=\,6\times10^{27}cm^{-2}s^{-1}$ and an interaction rate of 50 kHz, to be compared to the 8 kHz design interaction rate currently delivered by the LHC. The aim of ALICE is to cope with such a high interaction rate improving at the same time the resolution and the efficiency of the silicon tracker. In this context, one of the requirements for a prompt calibration of external detectors and to speed up the offline data processing is to run online the reconstruction of tracks in the Upgraded Inner Tracking System.
A new algorithm based on Cellular Automata has been developed to tackle this issue. In this algorithm the tracking is split in multiple phases to profit from data locality. At first, hit points are organised in sectors of azimuthal angle and longitudinal coordinate; then the algorithm looks for track segments within these sectors of the detector, independently. Track segments with compatible track parameters are marked as neighbours. Neighbouring track segments are then merged at the final stage using a set of rules defined by the Cellular Automaton mechanism, somewhat similar to the set of rules used in the Conway's Game of Life.
The obtained computing and tracking performance are compliant with the requirements of ALICE, being able to reconstruct tracks of transverse momentum down to 100 MeV$/c$ in events with high track density ($\mathrm{d}N/\mathrm{d}\eta$ up to 2000). The tracking and computing performance of this algorithm will be shown in the case of central Pb-Pb events at $\sqrt{s_{NN}}\,=\,5.5$ TeV.