Collectivity in large and small systems formed in ultrarelativistic collisions

Abstract

Collective flow of the final-state hadrons observed in ultrarelativistic heavy-ion collisions or even in smaller systems formed in high-multiplicity pp and p/d/${}^3$He-nucleus collisions is one of the most important diagnostic tools to probe the initial state of the system and to shed light on the properties of the short-lived, strongly-interacting many-body state formed in these collisions. Limited, in the initial years, to the study of mainly the directed and elliptic flows -- the first two Fourier harmonics of the single-particle azimuthal distribution -- this field has evolved in recent years into a much richer area of activity. This includes not only higher Fourier harmonics and multiparticle cumulants, but also a variety of other related observables, such as the ridge seen in two-particle correlations, flow decorrelation, symmetric cumulants and event-plane correlators which measure correlations between the magnitudes or phases of the complex flows in different harmonics, coefficients that measure the nonlinear hydrodynamic response, statistical properties, such as the non-Gaussianity of the flow fluctuations, etc. We present a Tutorial Review of the modern flow picture and the various aspects of the collectivity -- an emergent phenomenon in quantum chromodynamics.

Invited review article for EPJ ST, pedagogical review article, 34 pages, 14 Figs, 14 Exercises, comments welcome

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Cited by in corpus (9)

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• Observation of abnormal suppression of ${\mathrm{f}}_0$(980) production in p$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV
• Early time behavior of spatial and momentum anisotropies in kinetic theory across different Knudsen numbers
• Early time behavior of spatial and momentum anisotropies in a kinetic approach to nuclear collisions
• Two-particle correlations in azimuthal angle and pseudorapidity in central ${}^7$Be+${}^9$Be collisions at the CERN Super Proton Synchrotron
• Effect of transverse momentum conservation and flow on symmetric cumulants $s{c}_{2,3}\left\{4\right\}$ and $s{c}_{2,3,4}\left\{6\right\}$
• Dissociation-driven quarkonium spin alignment in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV
• Heavy quark polarization anisotropy as a novel probe of fireball geometry