Universal fluctuation-driven eccentricities in proton-proton, proton-nucleus and nucleus-nucleus collisions

Understand

We show that the statistics of fluctuation-driven initial-state anisotropies in proton-proton, proton-nucleus and nucleus-nucleus collisions is to a large extent universal.

• We propose a simple parametrization for the probability distribution of the Fourier coefficient $\varepsilon_n$ in harmonic $n$, which is in good agreement with Monte-Carlo simulations.
• Our results provide a simple explanation for the 4-particle cumulant of triangular flow measured in Pb-Pb collisions, and for the 4-particle cumulant of elliptic flow recently measured in p-Pb collisions.
• Both arise as natural consequences of the condition that initial anisotropies are bounded by unity.