Sub-leading flow modes in PbPb collisions at √sNN = 2.76 TeV from the HYDJET++ model

Abstract

Recent LHC results on the appearance of sub-leading flow modes in PbPb collisions at 2.76 TeV, related to initial-state fluctuations, are analyzed and interpreted within the HYDJET++ model. Using the newly introduced Principal Component Analysis (PCA) method applied to two-particle azimuthal correlations extracted from the model calculations, the leading and sub-leading flow modes are studied as a function of the transverse momentum (p(T)) over a wide centrality range. The leading modes of the elliptic (v(2)((1))) and triangular (v(3)((1))) flow calculated with the HYDJET++ model reproduce rather well the v(2){2} and v(3){2} coefficients measured experimentally using the two-particle correlations. Within the p(T) LT = 3 GeV/c range, where hydrodynamics dominates, the sub-leading flow effects are greatest at the highest p(T) of around 3 GeV/c. The sub-leading elliptic flow mode (v(2)((2))), which corresponds to the n = 2 harmonic, has a small non-zero value and slowly increases from central to peripheral collisions, while the sub-leading triangular flow mode (v(3)((2))), which corresponds to the n = 3 harmonic, is even smaller and does not depend on centrality. For n = 2, the relative magnitude of the effect measured with respect to the leading flow mode shows a shallow minimum for semi-central collisions and increases for very central and for peripheral collisions. For the n = 3 case, there is no centrality dependence. The sub-leading flow mode results obtained from the HYDJET++ model are in rather good agreement with the experimental measurements of the CMS Collaboration.