Azimuthal anisotropy harmonics in ultra-central PbPb collisions at sqrts_NN = 2.76 TeV

Azimuthal anisotropy harmonics have been measured in the ultra-central PbPb collisions at \rootsNN\ = 2.76\TeV by the CMS experiment during 2011 LHC PbPb run. The most central 0--0.2\% PbPb collisions have been collected using a unique trigger on total transverse energy in the hadronic forward calorimeters and total multiplicity of cluster hits in the silicon pixel tracker. A total of about 1.8 million events were recorded, corresponding to an integrated luminosity of 150~$\mu$b$^{-1}$. Fourier flow harmonics ($v_n$) are extracted from long-range dihadron correlations. Since the initial anisotropy of very central collisions has rather small theoretical uncertainties, these data provide strong constraints on transport properties of the medium such as the ratio of sheer viscosity to entropy density, $\eta/$s.