Heavy Ion Tea

Jet Tomographic Tests of the Hydro Initial State at RHIC and LHC
Azfar Adil(Columbia University)

Abstract: Current claims for the perfectly fluid nature of the strongly interacting QCD matter (sQGP) at RHIC are based on the success of non-viscous hydrodynamics in describing bulk low p⊥ collective observables [1]. These analyses, however, depend on the assumed initial state for hydrodynamic evolution being determined by the local participant density (ρPart (⊥ ; b)). Us- ing initial states corresponding to Color Glass Condensate (CGC) conditions in conjunction with non viscous hydrodynamics leads to a disagreement with data [2]. One thus needs an in- dependent test of the initial state before any statements can be made about the applicability of non viscous hydrodynamics at RHIC and the resultant perfect fluidity. We propose detailed jet tomography via the nuclear modification factor RAA(pT , φ, y ; b) as just such a test. CGC models generically lead to a higher spatial eccentricity in the trans- verse plane at mid rapidity than participant bulk models, which can be probed by high pT jets via jet quenching leading to an enhanced second fourier moment v2 (pT ; b) of RAA(pT , φ, 0; b). Furthermore, fpr y off midrapidity both CGC and participant bulk models predict a ‘twist’ in the medium, shifting it off the origin in the transverse plane, leading to a non zero first fourier moment v1 (pT , y ; b). We present calculations of these observations for RHIC and LHC and discuss their usefulness when it comes to differentiating initial states as well as their sensi- tivity to model details (e.g. nuclear edge effects). This presentation is based on work done in [3].

[1] T. Hirano, Acta. Phys. Polon., B36, p. 187-194, (2005) and references therein.

[2] T. Hirano, U. W. Heinz, D. Kharzeev, R. Lacey, and Y. Nara, Phys. Lett. B636, p. 299- 304, (2006).

[3] A. Adil, and M. Gyulassy, Phys. Rev. C72, 034907 (2005). A. Adil, M. Gyulassy, and T. Hirano, Phys. Rev. D73, 074006 (2006). A. Adil, H-J. Drescher, A. Dumitru, A. Hayashigaki, and Y. Nara, arXiv:nucl-th/0605012. A. Adil, M. Gyulassy, W. Horowitz and S. Wicks, in preparation.