  The luminosity measurement of the CMS experiment at the CERN LHC is
calibrated with Van der Meer (VdM) scans. A bias occurs in the VdM method due
to the assumption of transversely factorizable proton densities of the LHC
beams. Here, the different methods applied in Run 2 to estimate the size of the
factorization bias are reported. The beam-imaging method reconstructs the
transverse proton densities from beam-imaging scans. Additional methods exploit
offset scans, analyze the evolution of the measured luminous region, and
evaluate diagonal scans.
