Extracting the kinetic freeze-out properties of high energy pp collisions at the LHC with event shape classifiers

TL;DR

This study uses event shape classifiers and the Tsallis Blast-Wave model to analyze kinetic freeze-out properties in high-energy pp collisions at 13 TeV, revealing new insights into collective effects and flow signatures.

Contribution

It introduces the use of diverse event shape observables, especially flattenicity, to better understand kinetic freeze-out parameters and collective motion in pp collisions.

Findings

Consistent trends in freeze-out temperature across event shapes.

Flattenicity effectively isolates collective flow effects.

Expanded freeze-out parameter space with multiple event shape classifiers.

Abstract

Event shape measurements are crucial for understanding the underlying event and multiple-parton interactions (MPIs) in high energy proton-proton (pp) collisions. In this paper, the Tsallis Blast-Wave model with independent non-extensive parameters for mesons and baryons, was applied to analyze transverse momentum spectra of charged pions, kaons, and protons in pp collision events at $\sqrt{s}=13$ TeV classified by event shape estimators relative transverse event activity, unweighted transverse spherocity, and flattenicity. Our analysis reveals consistent trends in the kinetic freeze-out temperature and non-extensive parameter across different collision systems and event shape classes. The use of diverse event-shape observables in pp collisions has significantly expanded the accessible freeze-out parameter space, allowing for a more comprehensive exploration of its boundaries. Among these event shape classifiers, flattenicity emerges as a unique observable for disentangling hard process contributions from additive MPI effects, allowing the isolation of collective motion effects encoded by the radial flow velocity. Through the analysis of the interplay between event-shape measurements and kinetic freeze-out properties, we gain deeper insights into the mechanisms responsible for flow-like signatures in pp collisions.