Leading Track Underlying Event at 13 TeV

A detector level measurement of track distributions sensitive to the properties of the underlying event is presented. It is based on 9 million early Run 2 events collected using the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of $13$ TeV . Distributions of the track multiplicity, and of the track transverse momentum are measured in regions of azimuthal angle defined with respect to the leading track. The measured distributions are compared with predictions from Monte Carlo event generators.