Event and data persistency models for the LHCb Real Time Analysis System

¹ Physikalisches Institut, Ruprecht-Karls-Universitat Heidelberg, Heidelberg, Germany ;
² CERN ;
³ La Salle, Universitat Ramon Llull, Spain.

^* e-mail: michel.de.cian@cern.ch
^** e-mail: sevda.esen@cern.ch
^*** e-mail: arthur.hennequin@cern.ch
^**** e-mail: Xavier.Vilasis.Cardona@cern.ch

Published online: 6 May 2024

Abstract

Starting in 2022, the upgraded LHCb detector is collecting data with a pure software trigger. In its first stage, reducing the rate from 30MHz to about 1MHz, GPUs are used to reconstruct and trigger on B and D meson topologies and high-pT objects in the event. In its second stage, a CPU farm is used to reconstruct the full event and perform candidate selections, which are persisted for offline use with an output rate of about 10GB/s. Fast data processing, flexible and custom-designed data structures tailored for SIMD architectures and efficient storage of the intermediate data at various steps of the processing pipeline onto persistent media, e.g. tapes is essential to guarantee the full physics program of LHCb. We present the event model and data persistency developments for the trigger of LHCb in Run 3. Particular emphasis is given to the novel software-design aspects with respect to the Run 1+2 data taking, the performance improvements which can be achieved and the experience of restructuring a major part of the reconstruction software in a large HEP experiment.