Underlying Event Measurements with Leading Particles and Jets in pp collisions at $\sqrt{s} = 13$ TeV

A measurement of the underlying event (UE) activity is performed in proton-proton collisions at the centre-of-mass energy of 13 TeV with the CMS experiment at the LHC. The measurement is performed using leading charged-particles as well as leading charged-particle jets as reference objects. A leading charged-particle or charged-particle jet is required to be produced in the central pseudorapidity region ($|\eta| < 2$) and with transverse momentum $p_T \geq 0.5$ ($p_T^{jet} \geq 1$) GeV for leading charged-particle (charge particle jet). The UE activity is measured in terms of the average multiplicity and scalar sum of $p_T$ of the charged-particles, with $|\eta| < 2$ and $p_T \geq 0.5$ GeV, in the azimuthal region transverse to the direction of the leading reference object. The measurements are compared to predictions of several Monte Carlo event generators providing constraints on the modelling of the UE dynamics.