Using the ($2+1$)-dimensional viscous hydrodynamic code vish2$+$1 [H. Song and U. Heinz, Phys. Lett. B 658, 279 (2008); H. Song and U. Heinz, Phys. Rev. C 77, 064901 (2008); H. Song, Ph. D. thesis, The Ohio State University, 2009], we present systematic studies of the dependence of pion and proton transverse-momentum spectra and their elliptic flow in $200A$ GeV Au$+$Au collisions on the parameters of the hydrodynamic model (thermalization time, initial entropy density distribution, decoupling temperature, equation of state, and specific shear viscosity $\eta /s$). We identify a tension between the slope of the proton spectra, which (within hydrodynamic simulations that assume a constant shear viscosity to entropy density ratio) prefer larger $\eta /s$ values, and the slope of the $p_T$ dependence of charged hadron elliptic flow, which prefers smaller values of $\eta /s$. Changing other model parameters does not appear to permit dissolution of this tension.

• Received 9 October 2010

DOI:https://doi.org/10.1103/PhysRevC.82.054904