Effect of the shear viscosity to entropy density ratio on Hanbury-Brown–Twiss radii in a multiphase transport model

Using a multiphase transport (AMPT) model, we investigate the effect of shear viscosity to entropy density ratio on the Hanbury-Brown--Twiss (HBT) parameters and freeze-out eccentricity from the azimuthal angle dependence of the HBT radii with a constant specific shear viscous approach. The specific shear viscosity gives smaller values of ${R}_{\mathrm{o}},\phantom{\rule{0.16em}{0ex}}{R}_{\mathrm{l}}$ and ${R}_{\mathrm{o}}/{R}_{\mathrm{s}}$, but increases value of ${R}_{\mathrm{s}}$. The freeze-out eccentricity increases with decreasing $\ensuremath{\eta}/s$ which suggests a possible slow drop of ${\ensuremath{\varepsilon}}_{\mathrm{f}}$ in the excitation function with increasing energy in relativistic heavy-ion collisions.