LHCb begins using a unique approach to processing collision data in real time

Current technology does not allow to store and analyze all proton-proton collision data from the Large Hadron Collider (LHC). It is therefore necessary to filter the data according to the scientific goals of each experiment. Physicists call this selection process the “trigger”.

Therefore, data acquisition and analysis at the LHC is traditionally done in two steps. In the first, which physicists call “online,” the detector records the data, which is then read out by high-speed electronics and computers, and a selected fraction of the events are stored on floppy disks and magnetic tape.

Later, the stored events are analyzed “offline”. The offline analysis uses key data from the online process to determine the parameters used to set and calibrate the LHCb’s sub-detectors. This whole process takes a long time and consumes a large amount of human and computer resources.

To speed up and simplify this process, the LHCb collaboration made a revolutionary improvement in data acquisition and analysis. Using a new technique called real-time analysis, the process of fitting the sub-detectors takes place online automatically and the stored data is immediately available offline for physical analysis.

In LHC Run 2, LHCb’s trigger was a combination of high-speed electronics (“hardware triggers”) and computer algorithms (“software triggers”), and consisted of multiple stages. From the 30 million proton collisions per second (30 MHz) in the LHCb detector, the trigger system selected the more interesting collision events and finally reduced the amount of data to around 150 kHz. Various automated processes then used this data to calculate new parameters to adjust and calibrate the detector.

For Run 3 and beyond, the entire triggering system has changed radically: the hardware trigger has been removed and the entire detector is read out at the full LHC beam crossing rate of 40MHz. This allows LHCb to use real-time analysis on the entire data selection, making it much more precise and flexible.

The real-time reconstruction allows LHCb not only to pick events of interest, but also to compress the raw detector data in real-time. This means there is tremendous flexibility to select both the most interesting events and the most interesting parts of each event, making the most of LHCb’s computing resources. In the end, around 10 gigabytes of data will be permanently recorded every second and made available to physics analysts.

The success of the real-time analysis was only possible thanks to the exceptional work of the online and sub-detector teams during the construction and commissioning of this brand new version of the LHCb detector.