Event-by-event fluctuations of elliptic flow in ultrarelativistic O+O collisions

Abstract

We study O+O collisions at $\sqrt{s_\mathrm{NN}} = 5.36$ TeV within a fully three-dimensional $\text{McDipper}$+$\text{MUSIC}$ model, which allows us to describe the experimentally measured dependence of charged hadron multiplicity on centrality and pseudorapidity. We show that the initial elliptical eccentricity is mainly driven by the fluctuations of the energy deposition and thereby varies considerably event-by-event within a fixed centrality class. This also holds for elliptic flow $v_2$, whose origin in O+O thus differs from that in collisions of heavy nuclei. Using a decomposition of initial states in an average event and uncorrelated modes, we find that despite the large size of fluctuations we can reproduce the joint probability distribution of eccentricity and elliptic flow with a reasonable accuracy with only a small set of fluctuation modes.