Effect of an anisotropic escape mechanism on elliptic flow in relativistic heavy-ion collisions

We study the effect of an anisotropic escape mechanism on elliptic flow in relativistic heavy-ion collisions. We use the Glauber model to generate initial conditions and ignore hydrodynamic expansion in the transverse direction. We employ the Beer-Lambert law to allow for the transmittance of produced hadrons in the medium and calculate the anisotropy generated due to the suppression of particles traversing through the medium. To separate non-flow contribution due to surface bias effects, we ignore hydrodynamic expansion in the transverse direction and consider purely longitudinal boost-invariant expansion. We calculate the transverse momentum dependence of elliptic flow, generated from an anisotropic escape mechanism due to surface bias effects, for various centralities in $\sqrt{s_{NN}}=200$ GeV $\mathrm{Au}+\mathrm{Au}$ collisions at the Relativistic Heavy Ion Collider and $\sqrt{s_{NN}}=2.76$ TeV $\mathrm{Pb}+\mathrm{Pb}$ collisions at the Large Hadron Collider. We find that the surface bias effects make a sizable contribution to the total elliptic flow observed in heavy-ion collisions, indicating that the viscosity of the QCD matter extracted from hydrodynamic simulations may be underestimated.

Figure 1

Transverse momentum dependence of elliptic flow of charged hadrons for RHIC at various centralities. The symbols represent experimental results from PHENIX and STAR Collaborations. The theoretical curves are obtained by considering various values of attenuation length of hadrons in the medium. The error bars for the experimental data are contained within the symbol size.

Figure 2

Transverse momentum dependence of elliptic flow of charged hadrons for LHC at various centralities. The symbols represent experimental results from the ATLAS Collaboration. The theoretical curves are obtained by considering various values of attenuation length of hadrons in the medium. The error bars for the experimental data are contained within the symbol size.