Global quark polarization in noncentralA+Acollisions

Quark polarization in a viscous quark-gluon plasma

“…The initial parton production from this kind of model has approximate Bjorken scaling which will give rise to very small initial local longitudinal flow shear [17] except at very large rapidity region. Such small initial local longitudinal flow shear comes from the violation of the Bjorken scaling which one can use as the initial condition.…”

“…The estimates in Refs. [12,16,17] were based on the assumption that the initial quarks are not polarized. In order to discuss the time evolution of the quark polarization via multiple scattering, one must calculate the quark-quark cross section of initially polarized quarks.…”

“…Such a global (anti-)quark polarization should have many observable consequences such as global hyperon polarization [12,13], vector meson spin alignment [12,14] and the emission of circularly polarized photons [15]. Predictions have been made [12,[14][15][16][17] for these measurable quantities as functions of the global quark polarization P q . Experimental measurements of the Λ hyperon polarization with respect to the reaction plane at RHIC [18][19][20][21][22][23][24][25] place a limit |P Λ,Λ | 0.02 [19,24].…”

“…Experimental measurements of the Λ hyperon polarization with respect to the reaction plane at RHIC [18][19][20][21][22][23][24][25] place a limit |P Λ,Λ | 0.02 [19,24]. Such a limit puts a stringent test on both the initial shear of longitudinal flow in non-central heavy-ion collisions [17] as well as the time evolution of the polarization through transport processes.…”

“…[12] and in subsequent studies [16,17,26] were all obtained by considering the polarization process for a single scattering between quarks and thermal partons. However, one should consider the effect of the multiple scattering and expect that the quarks will be progressively polarized through multiple scattering.…”