During Run 3 of the LHC, likely to start in 2022, the upgraded LHCb experiment will use a triggerless readout system collecting data at an event rate of 30 MHz and a data rate of up to 40 Tbit/s. A software-only high level trigger will enable unprecedented flexibility for trigger selections.
During the first stage (HLT1), a sub-set of the full offline track reconstruction for charged particles is run to select events of interest based on single or two-track selections. This includes decoding the raw data, clustering of hits, pattern recognition, as well as track fitting, track classification with machine learning techniques and finally event selections.
The HLT1 will be processed entirely on GPUs, while the second high level trigger stage including a full track fit, full particle identification and hundreds of exclusive selections will be run on a CPU farm. The focus of this seminar will be the framework, reconstruction algorithms and performance of the GPU HLT1.