Evidence of Mass Ordering of Charm and Bottom Quark Energy Loss in Au+Au Collisions at RHIC

TL;DR

This study provides experimental evidence that charm and bottom quarks lose energy differently in a quark-gluon plasma, with bottom quarks experiencing less energy loss, confirming mass-dependent energy loss models in heavy-ion collisions.

Contribution

First measurement of nuclear modification factors for charm and bottom decay electrons at RHIC, demonstrating mass ordering of quark energy loss in a strongly coupled medium.

Findings

Bottom-decay electron $R_{AA}$ and $R_{CP}$ are higher than charm-decay electrons.

Data aligns with models including mass-dependent parton energy loss.

Evidence supports mass ordering of quark energy loss in quark-gluon plasma.

Abstract

Partons traversing the strongly interacting medium produced in heavy-ion collisions are expected to lose energy depending on their color charge and mass. We measure the nuclear modification factors for charm- and bottom-decay electrons, defined as the ratio of yields, scaled by the number of binary nucleon-nucleon collisions, in $\sqrt{s_{\rm NN}}$ = 200 GeV Au+Au collisions to $p$+$p$ collisions ($R_{\rm AA}$), or in central to peripheral Au+Au collisions ($R_{\rm CP}$). We find the bottom-decay electron $R_{\rm AA}$ and $R_{\rm CP}$ to be significantly higher than that of charm-decay electrons. Model calculations including mass-dependent parton energy loss in a strongly coupled medium are consistent with the measured data. These observations provide clear evidence of mass ordering of charm and bottom quark energy loss when traversing through the strongly coupled medium created in heavy-ion collisions.