Quark recombination and elliptic flow

Elliptic flow systematics for different hadron species have been explained by quark coalescence models. It has been argued that the elliptic asymmetry v_2 should scale with the number of quarks that comprise the hadron. We show how these arguments are sensitive to the relative role of asymmetries in the phase space density vs. asymmetries in the effective volume of emission. We also discuss the degree to which coalescence arguments differ from thermal models. Illustrative calculations based on solving the Boltzmann equation are presented along with the results of blast-wave models. Although the issue is complicated, ambiguities might be clarified by measurements of source-size parameters for nucleons at higher transverse momenta.