An estimate of QGP viscosity from STAR data on $\varphi$ mesons

In the Israel-Stewart’s theory of dissipative hydrodynamics, with a lattice based equation of state, where the confinement-deconfinement transition is a cross-over at $T_{co}$=196 MeV, we have analysed the STAR data on $\varphi$ meson production in Au+Au collisions at $\sqrt{s}$=200 GeV. From a simultaneous fit to $\varphi$ mesons multiplicity, mean $p_T$ and integrated $v_2$, we obtain a phenomenological estimate of QGP viscosity, $\eta \mathrm{/}s=0.15\pm 0.05\pm 0.03$, the first error is due to the experimental uncertainty in STAR measurements, the second reflects the uncertainties in initial and final conditions of the fluid. A host of STAR data, e.g. $\varphi$ multiplicity, integrated $v_2$, mean $p_T$, $p_T$ spectra ($p_T<$3 GeV), in central Au+Au collisions, are consistent with the estimate of viscosity.