Collectivity in heavy ion interactions at CMS

Investigations of anisotropic flow can provide us with necessary information about the initial state and the evolution of the deconfined strongly interacting matter called quark-gluon plasma (QGP). CMS measurements of flow harmonics and their fluctuations and (de)correlations cover a wide range of transverse momenta, pseudorapidity and centrality or event activity in different collision systems. The flow harmonics are measured using two- and multiparticle correlations. Although most measurements focus on the flow in the transverse plane at $y = 0$, studying event-by-event fluctuations along the longitudinal direction is interesting as well since they put constraints on the complete three-dimensional modeling of theinitial state used in 3+1D models of the QGP evolution. Event-by-event correlations between harmonics of different orders, studied, e.g., with mixed-harmonic and symmetric cumulants, measure the nonlinear hydrodynamic response and probe the onset of long-range collective multiparticle correlations, respectively. Statistical properties, such as the non-Gaussianity of the flow fluctuations, can be extracted by careful inspection of the data showing that there are small differences in the magnitudes of multiparticle cumulants. Identified flow measurements (e.g., that of light and heavy flavor quarks, or Z bosons, etc) provide an important insight into the nature of collective phenomena in different collision systems.