Underlying-event studies with strange hadrons in pp collisions at√s = 13 TeV with the ATLAS detector

Properties of the underlying-event in pp interactions are investigated primarily via the strange hadrons K 0 S, Λ and ¯Λ, as reconstructed using the ATLAS detector at the
LHC in minimum-bias pp collision data at √s = 13 TeV. The hadrons are reconstructed via the identification of the displaced two-particle vertices corresponding to the decay
modes K 0 S → π+π−, Λ → π− p and ¯Λ → π+ ¯p. These are used in the construction of underlying-event observables in azimuthal regions computed relative to the leading charged-particle jet in the event. None of the hadronisation and underlying-event physics models considered can describe the data over the full kinematic range considered. Events with a leading charged-particle jet in the range of 10 < p T ≤ 40 GeV are studied using the number of prompt charged particles in the transverse region. The ratio N (Λ + ¯Λ)/N (K 0 S ) as a function of the number of such charged particles varies only slightly over this range. This disagrees with the expectations of some of the considered Monte Carlo models.