  Precision luminosity measurements are essential to determine the fundamental
properties of the physics processes at the LHC. The estimation of the
integrated luminosity at the CMS experiment requires absolute scale calibration
of the luminometers, which is derived under special LHC machine setup. Series
of beam separation (van der Meer) scans are performed during these special
runs. The transverse profile of the overlap between the proton beams are
estimated by the continuous monitoring of the interaction rates together with
the beam properties. The dominant sources of systematic calibration uncertainty
are related to the precise estimation of the beam separation and the
non-factorizability of the proton density distributions in the transverse
direction. The correction factors and their uncertainties are extracted for
each effect and propagated to determine the final absolute scale and the
corresponding uncertainty. The obtained van der Meer scan calibration is
applied to the full physics data-taking period in order to estimate the
integrated luminosity. The latest results of the luminosity calibration studies
are reported from the CMS experiment.
