Underlying Event Measurements at ATLAS 

This talk presents ATLAS recent measurements of distributions sensitive to Underlying event, the hadronic activity observed in relationship with the hard scattering in the event using the full ATLAS dataset at center-of-mass energy of 13 TeV. Measurement of charged-particle distributions as a function of Upsilon momentum and different Upsilon states will be discussed. The measurement benefits from the heavy-ion style approach to remove combinatorial and pileup backgrounds leading to increased sensitivity. In addition, charged-particle distributions measured in top-antitop events decaying leptonically will be shown. The measured distributions can constrain models of color reconnection mechanism in Monte-Carlo generators.