Particle production as a function of the underlying event in pp collisions simulated with PYTHIA 8

In this workwe present the production of charged particles associatedwith high-?T trigger particles (8 < ? T < 15 GeV /2) at mid-pseudorapidity in proton-proton collisions at √ B = 5.02TeV simulated with the PYTHIA 8 Monte Carlo model. The study is performed as a function of the relative transverse activity classifier, 'T, which is the relative charged-particle multiplicity in the transverse region (c/3 < |Δq| < 2c/3) of the di-hadron correlations, and it is sensitive to the Multi-Parton Interactions. The evolution of the yield of associated particles on both the toward and the away regions with 3 ≤ ?assoc. T < 8 GeV/2 as a function of 'T is investigated. We propose a strategy which allows for the modelling and subtraction of the Underlying Event (UE) contribution from the toward and the away regions in challenging environments like those characterised by large 'T. We found that the signal in the away region becomes broader with increasing 'T. Contrarily, the yield increases with 'T in the toward region. This effect is reminiscent of that seen in heavy-ion collisions, where an enhancement of the yield in the toward region for 0− 5% central Pb–Pb collisions at √ BNN = 2.76TeV was reported. To further understand the role of the UE and additional jet activity, the transverse region is divided into two one-sided sectors, “trans-max” and “trans-min” selected in each event according to which region has larger or smaller charged particle multiplicity. Based on this selection criterion, the observables are studied as a function of 'max T and 'min T , respectively. The presented results have been published in Refs. [1, 2].