Apparent modification of the jet-like yield in proton–proton collisions with large underlying event

Abstract

Abstract This paper presents the production of charged particles associated with high-p T trigger particles ( 8 < p T t r i g . < 15 GeV/c) at midrapidity in proton–proton collisions at s = 5.02 TeV simulated with PYTHIA 8.244. The study is performed as a function of the relative transverse activity classifier, R T, which is the relative charged-particle multiplicity in the transverse region (π/3 < |ϕ trig. − ϕ assoc.| < 2π/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 towards and the away regions ( 3 ⩽ p T a s s o c . < 8 GeV/c) as a function of R T is investigated. We propose a strategy which allows for the modelling and subtraction of the underlying event contribution from the towards and the away regions in challenging environments like those characterised by large R T. We found that the signal in the away region becomes broader with increasing R T, while its corresponding yield is independent of R T. Contrarily, the yield increases with R T in the towards region. This effect is reminiscent of that seen in heavy-ion collisions, where an enhancement of the yield in the towards region for 0%–5% central Pb–Pb collisions at s N N = 2.76 TeV was reported. A discussion on the origin of these effects in PYTHIA, as well as their implications for the interpretation of recent LHC results for pp collisions, is presented.