King's College London

Research portal

Measurement of the distributions of event-by-event flow harmonics in lead-lead collisions at √sNN = 2.76 TeV with the ATLAS detector at the LHC

Research output: Contribution to journalArticle

ATLAS Collaboration

Original languageEnglish
Article number183
Pages (from-to)N/A
Number of pages56
JournalJournal of High Energy Physics
Issue number11
Publication statusE-pub ahead of print - Nov 2013

King's Authors


The distributions of event-by-event harmonic flow coefficients v n for n = 2- 4 are measured in sNN−−−−√ = 2.76 TeV Pb + Pb collisions using the ATLAS detector at the LHC. The measurements are performed using charged particles with transverse momentum p T > 0.5 GeV and in the pseudorapidity range |η| < 2.5 in a dataset of approximately 7 μb−1 recorded in 2010. The shapes of the v n distributions suggest that the associated flow vectors are described by a two-dimensional Gaussian function in central collisions for v 2 and over most of the measured centrality range for v 3 and v 4. Significant deviations from this function are observed for v 2 in mid-central and peripheral collisions, and a small deviation is observed for v 3 in 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. The v n distributions are also measured independently for charged particles with 0.5 < p T < 1 GeV and p T > 1 GeV. When these distributions are rescaled to the same mean values, the adjusted shapes are found to be nearly the same for these two p T ranges. The v n distributions 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.

View graph of relations

© 2018 King's College London | Strand | London WC2R 2LS | England | United Kingdom | Tel +44 (0)20 7836 5454