Abstract
Results of multi-particle cumulants for harmonic flow coefficients νn are obtained in sNN=5.02TeV Pb+Pb collisions with the ATLAS detector at the Large Hadron Collider. The cumulant ratios νn{4}/νn{2} for n = 2, 3 and 4 and ν2{6}/ν2{4} show centrality-dependent behavior compatible with eccentricity fluctuations. However, significant dependences on transverse momentum are observed, suggesting that flow fluctuations may also arise from final-state interactions. The flow cumulants are also found to depend on the resolution of the quantity used to define event centrality: poorer centrality resolution tends to increase the value of ν2{2} and changes the sign of ν2{4} and ν3{4} in ultra-central collisions. These results shed light on the contributions of flow fluctuations from the initial state and the final state, as well as on the influences of centrality fluctuations.
Highlights
Such final-state intra-event flow fluctuations may change the shape of p(vn) in a pT-dependent way and can be quantified by comparing cumulant ratio using particles from different pT ranges
Results of multi-particle cumulants for harmonic flow coefficients vn are obtained in sNN = 5.02 TeV Pb+Pb collisions with the ATLAS detector at the Large Hadron Collider
If vn ∝ n is exact, p(vn) should be the same as p( n) up to a rescaling factor. The latter is expected to cancel in the ratio of the cumulants such that the cumulant ratio reflects only the initial eccentricity fluctuations
Summary
Such final-state intra-event flow fluctuations may change the shape of p(vn) in a pT-dependent way and can be quantified by comparing cumulant ratio using particles from different pT ranges. These observables are obtained using two centrality definitions: the total transverse energy in the forward pseudorapidity range 3.2 < |η| < 4.9, ΣET, and the number of reconstructed charged particles in the midrapidity range |η| < 2.5, Ncrehc.
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