The upgraded LHCb experiment at CERN will run without a hardware level trigger in 2021, resulting in the complete detector being read out at the full bunch-crossing rate of 30 MHz and a maximum data rate of 40 Tbit/s. Events of interest are selected with a software-only trigger in two stages.
During the first trigger stage, High Level Trigger 1 (HLT1), a sub-set of the full offline track reconstruction for charged particles is run to select particles of interest based on single or two-track selections.
This allows unprecedented flexibility for trigger selections but at the same time poses a significant computing challenge.
The “Allen” project is capable of processing the full HLT1 on about 500 state of the art graphics processing units (GPUs).
Allen therefore enables the exploitation of LHCb’s broad physics program in Run 3.
I will discuss the concept of performing a full event selection on GPUs and
introduce the framework and algorithms we have developed for this task.
As the first complete high-rate GPU trigger, Allen has the potential to significantly impact the trigger systems of other HL-LHC experiments,
as well as experiments at future facilities and colliders.
