Determining initial-state fluctuations from flow measurements in heavy-ion collisions

We present a number of independent flow observables that can be measured using multiparticle azimuthal correlations in heavy-ion collisions. Some of these observables are already well known, such as ${v}_{2}{2}$ and ${v}_{2}{4}$, but most are new---in particular, joint correlations among ${v}_{1}$, ${v}_{2}$, and ${v}_{3}$. Taken together, these measurements will allow for a more precise determination of the medium properties than is currently possible. In particular, by taking ratios of these observables, we construct quantities that are less sensitive to the hydrodynamic response of the medium and thus more directly characterize the initial-state fluctuations of the event shape, which may constrain models for early-time, nonequilibrium QCD dynamics. We present predictions for these ratios using two Monte Carlo models and compare them to available data.

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