Collective flow and charged hadron correlations in 2.76 TeV PbPb collisions at CMS

We report on the CMS measurements of charged-hadron anisotropic azimuthal distributions from PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The results are presented as a function of transverse momentum, centrality and pseudorapidity over a wide kinematic region. For low transverse momentum particles ($p_{\rm T} < 3~{\rm GeV/c}$ ) the azimuthal behavior is believed to be dominated by the hydrodynamic flow of the expanding medium created in the reaction. We characterize this behavior in terms of the first-order term of a Fourier expansion of the azimuthal angular distribution as determined using the event-plane, cumulant, and Lee-Yang zeros methods. For high transverse momentum particles ($p_{\rm T} > 8~{\rm GeV/c}$) the azimuthal asymmetry reflects the energy loss of high-energy partons moving through the medium. This is studied using the event-plane method. In both cases the azimuthal asymmetry can be related to the initial geometry of the hot and dense matter created in the reaction. These results provide constraints on theoretical descriptions of the early dynamics of heavy-ion reactions at the LHC and the transport properties through the medium created by these reactions.