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Compact Muon Solenoid
LHC, CERN

CMS-PAS-HIN-15-010
Principal component analysis of two-particle azimuthal correlations in PbPb and pPb collisions at CMS
Abstract: A Principle Component Analysis (PCA) of two-particle azimuthal correlations as a function of transverse momentum (pT) is presented in PbPb collisions at 2.76 TeV and high-multiplicity pPb collisions at 5.02 TeV. The data were recorded using the CMS detector at the LHC. It has recently been shown that factorization breaking of two-particle azimuthal correlations can be attributed to the effect of initial-state fluctuations. Using a PCA approach, Fourier coefficients of observed two-particle azimuthal correlations as a function of both particles pT are characterized into leading and sub-leading mode terms. The leading modes are essentially equivalent to anisotropy harmonics (vn) previously extracted from two-particle correlation methods as a function of pT. The sub-leading modes represent the largest sources of factorization breaking. In the context of hydrodynamic models, they are a direct consequence of initial-state fluctuations, particularly providing new insights on the radial excitations of initial-state eccentricity. The results are presented over a wide range of centrality and event multiplicity. Connection to the measurement of pT-dependent flow factorization breaking is also discussed.
CMS Publications
Compact Muon Solenoid
LHC, CERN