We report on the application of a cascade + viscous hydro + cascade model for heavy ion collisions in the RHIC Beam Energy Scan range, $sqrt{s_{rm NN}}=6.3dots200$ GeV. By constraining model parameters to reproduce the data we find that the effective(average) value of the shear viscosity over entropy density ratio $eta/s$ decreases from 0.2 to 0.08 when collision energy grows from $sqrt{s_{rm NN}}approx7$ to 39 GeV.
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