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

Abstract

We study whether it is possible to use high-p⊥ data/theory to constrain the temperature dependence of the shear viscosity over entropy density ratio η/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⊥ RAA and flow coefficients v2, v3, and v4 assuming different (η/s)(T ) of the fluid-dynamically evolving medium. (ii) We calculate the quenching strength ( ˆq/T 3) from our dynamical energy loss model and convert it to η/s as a function of temperature. It turned out that the first approach cannot distinguish between different (η/s)(T ) assumptions when the evolution is constrained to reproduce the low-p⊥ data. In distinction, (η/s)(T ) calculated using the second approach agrees surprisingly well with the (η/s)(T ) inferred through state-of-the-art Bayesian analyses of the low-p⊥ data even in the vicinity of Tc, while providing much smaller uncertainties at high temperatures.