Heavy flavor puzzle at RHIC: analysis of the underlying effects

TL;DR

This paper investigates the heavy flavor puzzle at RHIC, revealing that fragmentation and decay effects cause a reversal in suppression hierarchy, explaining why neutral pions and single electrons show similar suppression despite expectations.

Contribution

The study identifies the roles of fragmentation and decay functions in reversing suppression hierarchy, providing an intuitive explanation for the RHIC heavy flavor puzzle.

Findings

Reversal in suppression hierarchy between neutral pions and D mesons.

Fragmentation functions deform light parton suppression patterns.

Decay functions align single electron suppression with D meson suppression.

Abstract

Suppressions of light and heavy flavor observables are considered to be excellent probes of QCD matter created in ultra-relativistic heavy ion collisions. Suppression predictions of quark and gluon jets appear to suggest a clear hierarchy according to which neutral pions should be more suppressed than D mesons, which in turn should be more suppressed than single electrons. However, joint comparison of neutral pion (light probe) and non-photonic single electron (heavy probe) suppression data at RHIC unexpectedly showed similar jet suppression for these two probes, which presents the well-known heavy flavor puzzle at RHIC. We here analyze which effects are responsible for this unexpected result, by using the dynamical energy loss formalism. We find that the main effect is a surprising reversal in the suppression hierarchy between neutral pions and D mesons, which is due to the deformation of the suppression patterns of light partons by fragmentation functions. Furthermore, we find that, due to the decay functions, the single electron suppression approaches the D meson suppression. Consequently, we propose that these two effects, taken together, provide a clear intuitive explanation of this longstanding puzzle.