Quasiparticle degrees of freedom versus the perfect fluid as descriptors of the quark-gluon plasma

The hot nuclear matter created at the Relativistic Heavy Ion Collider has been characterized by near-perfect fluid behavior. We demonstrate that this stands in contradiction to the identification of quantum chromodynamics quasiparticles with the thermodynamic degrees of freedom in the early (fluid) stage of heavy-ion collisions. The empirical observation of constituent quark "n(q)" scaling of elliptic flow [PHENIX, A. Adare , Phys. Rev. Lett. 98, 162301 (2007)] is juxtaposed with the lack of such scaling behavior in hydrodynamic fluid calculations followed by Cooper-Frye freeze-out to hadrons. As the hydrodynamic fluid expands, increasing viscous effects may allow for a short time period of "quasiparticle transport" prior to hadronization. However, without a detailed understanding of the transitions between these time stages, the "n(q)" scaling is not a necessary consequence of this prescription. Also, if the duration of this stage is too short, it may not support well-defined quasiparticles. By comparing and contrasting the coalescence of quarks into hadrons with the similar process of producing light nuclei from nucleons, it is shown that the observation of "n(q)" scaling in the final state does not necessarily imply that the constituent degrees of freedom were the relevant ones in the initial state.