The CBM First-level Event Selector
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 10 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 performs on-line a full event reconstruction on the 1 TB/s input data stream. The current architecture foresees a scalable high performance computer, expanding on the experience gained in the ALICE HLT system. In order 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 for hit combination and detection and GPUs for the later track reconstruction.
One particular issue is the orchestration of the data flow in order to avoid unnecessary congestion. The FLES key aspects, as envisioned today are: