Cross section measurements for heavy-ion collision processes require a precise estimate of the
integrated luminosity of the recorded data set. During the 2015 - 2018 data-taking period (“Run
2”) of the LHC, lead-lead, proton-lead, and proton-proton collisions at the reference energy of
5.02 TeV per nucleon pair were recorded with the CMS experiment. For these data sets, the
luminosity measurements are reported. The absolute luminosity scale is calibrated with beam-separation (“van der Meer”) scans, performed separately for each collision system. Several
sources of systematic bias are studied and corrected for in the analysis of the van der Meer scan
data to improve the precision of the luminosity measurement. When applying the calibrations to
the entire data-taking period, a substantial contribution to the total uncertainty in the integrated
luminosity originates from the measurement of the detector stability. A total systematic uncertainty
of 1.5% has been reached for the PbPb data recorded in 2018.