Wei Li (MIT)
Azimuthal anisotropy harmonics have been measured in ultra-central PbPb collisions at a center-of-mass energy per nucleon pair of 2.76 TeV. Top central 0.2\% PbPb collisions have been collected using a unique trigger on total energy at forward hadronic calorimeter and total multiplicity of hits on pixel tracker by the CMS experiment during 2011 LHC PbPb run. A total of about 1.8 million events were recorded with top 0.2\% collision centrality. Fourier flow harmonics ($v_n$) are extracted from Fourier decomposition of long-range dihadron correlations as a function of particle transverse momentum. The relative ratio of different $v_n$ provides a direct constraint on the eta/s of the QGP matter, independent of the initial condition models.
Collaboration CMS (CERN)