Abstract

Luminosity measurements are foundational elements of collider physics measurements and searches. Its precise determination is essential for accurate cross-section measurements and new physics searches. In this talk, the most precise luminosity measurement ever achieved at a bunched-beam hadron collider, based on data collected by the CMS experiment during the LHC Run 2 (2015-2018) at sqrt(s) = 13 TeV. Leveraging van der Meer scans, advanced extrapolation techniques, and a suite of calibrated luminometers, CMS reached a relative uncertainty of 0.82% for 2017 and 0.84% for 2018. Combining these updated measurements with the previous 2015 and 2016 precision publications, the CMS luminosity for Run 2 data is just 0.73%—a new benchmark in collider performance. We detail the methodology behind the beam-separation (van der Meer) scans, corrections for detector nonlinearity and efficiency, and the use of Z boson rates to cross check consistency across multiple data-taking periods. This achievement not only enhances the precision of CMS physics results but also establishes a new standard for future luminosity determinations at high-energy colliders.