Luminosity determination for low-pileup datasets at $\sqrt{s}=5$ and 13 TeV using the ATLAS detector at the LHC

This note describes the preliminary determination of the integrated luminosity for dedicated $pp$ collision samples recorded with low pileup at $\sqrt{s}=5$ and 13 TeV by the ATLAS detector at the LHC in 2017-2018. The absolute luminosity scale was determined using van der Meer scans recorded for each dataset and beam energy, and extrapolated to the low-pileup physics data-taking regime using complementary measurements from several luminosity-sensitive detectors. The total uncertainty on the integrated luminosity of the 257 pb$^{-1}$ $\sqrt{s}=5$ TeV sample recorded in 2017 is 1.6 %, and that on the combined 335 pb$^{-1}$ $\sqrt{s}=13$ TeV sample from 2017 and 2018 is 1.5 %.