A Comprehensive Bandwidth Testing Framework for the LHCb Upgrade Trigger System

¹ Department of Physics, University of Warwick, Coventry, United Kingdom
² Faculty of Mathematics and Computer Science, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
³ European Organization for Nuclear Research (CERN), Geneva, Switzerland
⁴ Department of Physics, University of Oxford, Oxford, United Kingdom

^* email: ross.john.hunterATcern.ch

Published online: 7 October 2025

Abstract

The LHCb experiment at CERN has undergone a comprehensive upgrade, including a complete re-design of the trigger system into a hybrid-architecture, software-only system that records ten times more events per unit time for physics analysis than its predecessor. This increased efficiency - as well as the growing diversity of signals physicists want to analyse - makes it more challenging to conform to crucial operational targets on bandwidth and storage capacity. To address this, a comprehensive, automated testing framework has been developed that emulates the entire LHCb trigger and offline-processing software stack on simulated and real collision data. Scheduled both nightly and on-demand by software testers during development, these tests measure the onlineand offline-processing’s key operational performance metrics (such as rate and bandwidth), for each of the system’s 4000 distinct physics selection algorithms, and their cumulative totals. The results are automatically delivered via concise summaries - to GitLab merge requests and instant messaging channels - that further link to an extensive dashboard of per-algorithm information. The dashboard and pages therein facilitate test-driven trigger development by 100s of physicists, whilst the concise summaries enable efficient, data-driven decision-making by management and software maintainers. This novel bandwidth-testing framework has been helping LHCb build an operationallyviable trigger and data-processing system whilst maintaining the efficiency to satisfy its physics goals.