Unveiling the effects of multiple soft partonic interactions in pp collisions at 13.6 TeV using charged-particle flattenicity

by Antonio Ortiz Velasquez (U. Mexico)

Tuesday 18 Oct 2022, 11:00 → 12:00 Europe/Stockholm

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 notorious since the discovery of fluid-like behaviour in high-multiplicity pp collisions. In particular, the analysis as a function of the charged-particle multiplicity registered in the forward V0 ALICE detector allowed for the discovery of strangeness enhancement in pp collisions. However, one limitation of these event classifiers is that requiring a high charged-particle multiplicity within a narrow pseudorapidity interval biases the sample towards hard processes like multi-jet final states. This limitation of the existing event classifiers makes it difficult to perform jet-quenching searches in high-multiplicity pp collisions. In this seminar I will discuss the use of a new event classifier called flattenicity aimed at quantifying the shape of the event using the information in both azimuthal angle and pseudorapidity.  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.