CMS-PAS-HIN-15-010

CMS-PAS-HIN-15-010
Principal component analysis of two-particle azimuthal correlations in PbPb and pPb collisions at CMS
CMS Collaboration
September 2015

Abstract: A Principle Component Analysis (PCA) of two-particle azimuthal correlations as a function of transverse momentum ($p_{\mathrm T}$) 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 $p_{\mathrm T}$ are characterized into leading and sub-leading mode terms. The leading modes are essentially equivalent to anisotropy harmonics ($v_n$) previously extracted from two-particle correlation methods as a function of $p_{\mathrm T}$. 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 $p_{\mathrm T}$-dependent flow factorization breaking is also discussed.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PRC 96 (2017) 064902. The superseded preliminary plots can be found here.

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