Unveiling the effects of multiple soft partonic interactions in pp collisions at $\sqrt{{\textit s}}=13.6$ TeV using charged-particle flattenicity

Abstract

Event classifiers based either on the charged-particle multiplicity or the event shape have been extensively used in proton-proton (pp) collisions by the ALICE collaboration at the LHC. The use of these tools became very instrumental since the observation of fluid-like behavior in high-multiplicity pp collisions. In particular, the study as a function of the charged-particle multiplicity registered in the forward V0 ALICE detector allowed for the discovery of strangeness enhancement in high-multiplicity pp collisions. However, one drawback of the multiplicity-based event classifiers is that requiring a high charged-particle multiplicity biases the sample towards hard processes like multi-jet final states. These biases make it difficult to perform jet-quenching searches in high-multiplicity pp collisions. In this context, the present paper explores the use of the new event classifier, flattenicity; which uses the multiplicity calculated in the forward pseudorapidity region. To illustrate how this tool works, pp collisions at $\sqrt{s}=13.6$ TeV simulated with PYTHIA~8 are explored. The sensitivity of flattencity to multi-partonic interactions as well as to the ``hardness'' of the collision are discussed. PYTHIA 8 predictions for the transverse momentum spectra of light- and heavy-flavored hadrons as a function of flattenicity are presented.