A First-level Event Selector for the CBM Experiment at FAIR

The CBM experiment at the upcoming FAIR accelerator aims to create highest baryon densities in nucleus-nucleus collisions and to explore the properties of super-dense nuclear matter. Event rates of 1 0 MHz are needed for high-statistics measurements of rare probes, while event selection requires complex global triggers like secondary vertex search. To meet these demands, the CBM experiment uses self-triggered detector front-ends and a data push readout architecture. The First-level Event Selector (FLES) is the central physics selection system in CBM. It receives all hits and performs online event selection on the 1 TByte/s input data stream. The event selection process requires high-throughput event building and full event reconstruction using fast, vectorized track reconstruction algorithms. The current FLES architecture foresees a scalable high-performance computer. To achieve the high throughput and computation efficiency, all available computing devices will have to be used, in particular FPGAs at the first stages of the system and heterogeneous many-core architectures such as GPUs for efficient track reconstruction. A high-throughput network infrastructure and flow control in the system are other key aspects. In this paper, we present the foreseen architecture of the First-level Event Selector.