Heavy Flavors and Quarkonia at RHIC
After the discovery of the strongly coupled quark-gluon plasma (QGP), a nearly perfect fluid, in 200 GeV Au+Au collisions at RHIC, understanding its microscopic structure and transport properties has become a central goal of relativistic heavy-ion physics. Heavy-flavor particles, containing charm or bottom quarks, provide unique sensitivity to the QGP because they are produced predominantly in the initial hard scatterings and interact with the medium throughout its evolution. This review summarizes measurements of open heavy flavor and quarkonia by the PHENIX and STAR experiments, focusing primarily on 200 GeV collisions recorded during the first two decades of RHIC operations. We discuss key results on charm, bottom, and quarkonium production cross sections; cold nuclear matter effects in small collision systems; nuclear modification factors and elliptic flow of open heavy-flavor hadrons; charm baryon-to-meson production ratios; and the suppression patterns of quarkonium states in Au+Au collisions. We further highlight the resulting insights into the properties of the QGP, including heavy-quark transport, hadronization mechanisms, and quarkonium dissociation and regeneration in the medium. Finally, we discuss the future prospects of the RHIC heavy-flavor program, enabled by the large data sets collected by the STAR and sPHENIX experiments, and its strong synergy with the future Electron-Ion Collider, where precision measurements of heavy-flavor production in electron--proton and electron--nucleus collisions will provide complementary constraints on the structure of QCD matter.