Measurement of the distributions of event-by-event flow harmonics in lead-lead collisions at $ \sqrt{{{s_{NN }}}} $ = 2.76 TeV with the ATLAS detector at the LHC

Abstract The distributions of event-by-event harmonic flow coefficientsvnforn= 2- 4 are measured in $ \sqrt{{{s_{NN }}}} $ = 2.76 TeV Pb + Pb collisions using the ATLAS detector at the LHC. The measurements are performed using charged particles with transverse momentumpT>0.5 GeV and in the pseudorapidity range |η|<2.5 in a dataset of approximately 7μb−1recorded in 2010. The shapes of thevndistributions suggest that the associated flow vectors are described by a two-dimensional Gaussian function in central collisions forv2and over most of the measured centrality range forv3andv4. Significant deviations from this function are observed forv2in mid-central and peripheral collisions, and a small deviation is observed forv3in mid-central collisions. In order to be sensitive to these deviations, it is shown that the commonly used multi-particle cumulants, involving four particles or more, need to be measured with a precision better than a few percent. Thevndistributions are also measured independently for charged particles with 0.5< pT<1 GeV andpT>1 GeV. When these distributions are rescaled to the same mean values, the adjusted shapes are found to be nearly the same for these twopTranges. Thevndistributions are compared with the eccentricity distributions from two models for the initial collision geometry: a Glauber model and a model that includes corrections to the initial geometry due to gluon saturation effects. Both models fail to describe the experimental data consistently over most of the measured centrality range.

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