Leading and Sub-Leading Flows At the Lhc from the Cms

Abstract

The initial state fluctuations of the colliding heavy-ion nuclei play a major role in understanding the anisotropic flow of final state particles. Furthermore, an important signature of these fluctuations is the flow (event plane) angle dependence from p(T) that induces a measurable effect of factorization breaking in a pure relativistic hydrodynamic picture. Here, the effect of factorization breaking is described using a new method based on principal component analysis (PCA) and two-particle correlations. The method exposes leading and sub-leading mode, the leading corresponding to the standard elliptic and triangular flow and the sub-leading representing a new variable that is a direct response to initial state fluctuations. In this study, first measurements of the subflow are presented, as a function of transverse momentum in PbPb collisions at root s(NN) = 2.76 TeV and high-multiplicity pPb collisions at. root s(NN) = 5.02 TeV with CMS data.