Constraining η/s through high- p⊥ theory and data

We study whether it is possible to use high-${p}_{\ensuremath{\perp}}$ data/theory to constrain the temperature dependence of the shear viscosity over entropy density ratio $\ensuremath{\eta}/s$ of the matter formed in ultrarelativistic heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). We use two approaches: (i) We calculate high-${p}_{\ensuremath{\perp}}\phantom{\rule{4pt}{0ex}}{R}_{AA}$ and flow coefficients ${v}_{2}, {v}_{3}$, and ${v}_{4}$ assuming different $(\ensuremath{\eta}/s)(T)$ of the fluid-dynamically evolving medium. (ii) We calculate the quenching strength ($\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}/{T}^{3}$) from our dynamical energy loss model and convert it to $\ensuremath{\eta}/s$ as a function of temperature. It turned out that the first approach cannot distinguish between different $(\ensuremath{\eta}/s)(T)$ assumptions when the evolution is constrained to reproduce the low-${p}_{\ensuremath{\perp}}$ data. In distinction, $(\ensuremath{\eta}/s)(T)$ calculated using the second approach agrees surprisingly well with the $(\ensuremath{\eta}/s)(T)$ inferred through state-of-the-art Bayesian analyses of the low-${p}_{\ensuremath{\perp}}$ data even in the vicinity of ${T}_{c}$, while providing much smaller uncertainties at high temperatures.