CMS luminosity measurement using nucleus-nucleus collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}=5.02\,\text{TeV}$ in 2018

The measurement of the luminosity delivered to the CMS experiment during the lead-lead (PbPb) data-taking period in 2018 at nucleon-nucleon center-of-mass energy of $5.02\,\text{TeV}$ is presented. Three subdetectors are used: the Fast Beam Conditions Monitor, the forward hadron calorimeter, and the Pixel Luminosity Telescope. The absolute luminosity is determined by integrating the subdetector rate as a function of beam separation, using the so-called van der Meer (vdM) technique. Adding in quadrature independent sources of systematic uncertainty we estimate an overall vdM precision of $1.3\%$, with the dominant source related to the transverse factorizability of the bunch density profiles. The total uncertainty of $1.5\%$ is then obtained including time stability of the vdM-calibrated subdetector response. Short vdM-like scans, performed regularly in CMS during the PbPb data-taking period, are studied.