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

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.