CMS luminosity measurement using nucleus-nucleus collisions in Run 2

Material about the calibration of the luminosity delivered to the CMS experiment during the lead-lead (PbPb) and xenon-xenon (XeXe) data-taking periods in 2018 and 2017 at nucleon-nucleon center-of-mass energies of 5.02 and 5.44 TeV, respectively, is presented. Three subdetectors are highlighted: the Fast Beam Conditions Monitor (BCM1F), the forward hadron calorimeter (HF), and the Pixel Luminosity Telescope (PLT). For the PbPb data set, the absolute luminosity is determined by integrating the subdetector rate as a function of beam separation, using the the so-called van der Meer (vdM) scan technique. Corrections and their uncertainty are derived based on a series of additional types of scans. One of the so-far dominant source of systematic uncertainty is related to the horizontal-vertical factorization of the bunch density profiles. The total uncertainty includes time stability of the vdM-calibrated subdetector response. Short vdM-like ("emittance") scans, performed in CMS during both the PbPb and XeXe data-taking periods, are studied and considered as promising alternative technique also for planned data-taking periods with lighter nuclei.