Explaining the fine hierarchy in pion and kaon suppression at LHC: Importance of fragmentation functions

TL;DR

This paper investigates the hierarchy of suppression between pions and kaons in LHC heavy-ion collisions, emphasizing the critical role of fragmentation functions in accurately modeling and explaining the observed experimental data.

Contribution

It demonstrates that the choice of fragmentation functions is crucial for theoretical models to correctly reproduce the fine hierarchy in particle suppression observed at LHC.

Findings

Most fragmentation functions reverse the observed hierarchy

Recent fragmentation functions accurately reproduce the hierarchy

Theoretical predictions now align well with detailed experimental data

Abstract

We here concentrate on available $\pi^\pm$ and $K^\pm$ ALICE preliminary $R_{AA}$ data in central 2.76 TeV Pb+Pb collisions at LHC. These data show an interesting fine resolution hierarchy, i.e. the measured $K^\pm$ data have consistently lower suppression compared to $\pi^\pm$ measurements. We here ask whether theoretical predictions based on energy loss in dynamical QCD medium can quantitatively and qualitatively explain such fine resolution. While our suppression calculations agree well with the data, we find that qualitatively explaining the fine hierarchy critically depends on the choice of fragmentation functions. While the most widely used fragmentation functions lead to the reversal of the observed hierarchy, a more recent version correctly reproduce the experimental data. We here point to the reasons behind such discrepancy in the predictions. Our results argue that accuracy of the theoretical predictions reached a point where comparison with fine resolution data at LHC can generate useful understanding.