Elliptic flow from a transversally thermalized fireball
Abstract
The agreement of elliptic flow data at RHIC at central rapidity with the hydrodynamic model has led to the conclusion of very rapid thermalization. This conclusion is based on the intuitive argument that hydrodynamics, which assumes instantaneous local thermalization, produces the largest possible elliptic flow values and that the data seem to saturate this limit. We here investigate the question whether incompletely thermalized viscous systems may actually produce more elliptic flow than ideal hydrodynamics. Motivated by the extremely fast primordial longitudinal expansion of the reaction zone, we investigate a toy model that exhibits thermalization only in the transverse directions but undergoes collisionless freestreaming expansion in the longitudinal direction. For collisions at RHIC energies, elliptic flow results from the model are compared with those from hydrodynamics. With the final particle yield and k_{⊥} distribution fixed, the transversally thermalized model is shown not to be able to produce the measured amount of elliptic flow. This investigation provides further support for very rapid local kinetic equilibration at RHIC. It also yields interesting novel results for the elliptic flow of massless particles such as direct photons.
 Publication:

Physical Review C
 Pub Date:
 July 2002
 DOI:
 10.1103/PhysRevC.66.014907
 arXiv:
 arXiv:hepph/0205058
 Bibcode:
 2002PhRvC..66a4907H
 Keywords:

 25.75.Ld;
 24.10.Nz;
 24.85.+p;
 Collective flow;
 Hydrodynamic models;
 Quarks gluons and QCD in nuclei and nuclear processes;
 High Energy Physics  Phenomenology;
 High Energy Physics  Experiment;
 High Energy Physics  Theory;
 Nuclear Experiment;
 Nuclear Theory
 EPrint:
 revtex4, 15 pages + 10 embedded EPS figures