Speaker
Description
During data-taking, LHCb optimizes physics performance by levelling the instantaneous luminosity within each fill, steering the transverse beam separation. In Run 3, the experiment transitioned to a fully software-based trigger and routine operation at an instantaneous luminosity about five times larger than in previous runs, requiring upgraded strategies for real-time monitoring and offline absolute calibration.This contribution reviews the Run-3 luminosity framework, centred on the dedicated PLUME luminometer and complemented by a set of online proxies from nearly all sub-detectors, providing both integrated and bunch-by-bunch luminosity for operations. PLUME has demonstrated robust performance (DAQ efficiency above 99% during 2024 data taking) and serves as a reference for cross-calibrating backup systems and sub-detector-based proxies. In parallel, dedicated luminosity trigger lines record offline-quality observables in a specialised 30 kHz stream, enabling precise offline calibration and systematic cross-checks of linearity and long-term stability. We also summarise key Run-2 absolute calibration developments based on van der Meer scans. Recent studies using beam-gas imaging to calibrate DOROS beam-position monitors provide beam-displacement measurements at IP8 with sub-micron precision, improving control of length-scale and orbit-drift systematics relevant to reference cross-section determinations. Finally, we present updated Run-3 results, including the latest beam-gas-imaging measurement of the ghost-charge fraction.
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