Abstract
The LHC results on the 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 the sub-leading flow modes are studied as a function of the transverse momentum (pT ) over a wide centrality range. The leading modes of the elliptic (v(1)2) and triangular (v3(1)3) flow calculated within the HYDJET++ model reproduce rather well the v2{2} and v3{2} coeffcients experimentally measured using the two-particle correlations. Within the pT ≤3 GeV/c range where hydrodynamics dominates, the sub-leading flow effects are greatest at the highest pT of around 3 GeV/c. The sub-leading elliptic flow mode (v2(2)), which corresponds to n=2 harmonic, has a small non-zero value and slowly increases from central to peripheral collisions, while the sub-leading triangular flow mode (v3(2)), which corresponds to 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 n =3 case, there is no centrality dependence. The subleading flow mode results obtained from the HYDJET++ model are in a rather good agreement with the experimental measurements of the CMS Collaboration.
Highlights
At sufficiently high energy density achieved in ultra-relativistic heavy-ion collisions, a new state of matter, called Quark-Gluon-Plasma (QGP), is created
In order to check the consistency of extracted vn harmonics using the method of Principal Component Analysis (PCA) and one of the standard approaches given by Eq (2), as well as to perform a PCA analysis in order to extract the leading and sub-leading flow modes, the two-particle correlation functions defined by the Eq (6) are constructed
The PCA method for studying flow, by its construction, may fully exploits the information contained in the covariance matrix formed from the two-particle Fourier coefficients and may provide high sensitivity to the standardly defined flow measurements, and to the influence of the initial-state fluctuations to the hydrodynamic flow
Summary
At sufficiently high energy density achieved in ultra-relativistic heavy-ion collisions, a new state of matter, called Quark-Gluon-Plasma (QGP), is created. The anisotropy is described by Fourier decomposition of the azimuthal angle (φ) hadron distribution [1,2,3] dN dφ ∝. EPJ Web of Conferences final-state particle density. The second order Fourier coefficient, v2, is called elliptic flow. The angle Ψ2 corresponds to the flow symmetry plane spanned over the beam direction and the shorter axis of the roughly elliptical shape of the nucleon overlap region. The collective behavior of the QGP has been studied using the azimuthal anisotropy of particles detected at experiments at the Relativistic Heavy Ion Collider (RHIC) [5,6,7]. The studies have been continued with the experiments [8,9,10,11,12,13,14,15,16,17,18,19] at the Large Hadron Collider (LHC) at significantly higher collision energies
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