Non-Gaussian eccentricity fluctuations

TL;DR

This paper investigates the non-Gaussian fluctuations of anisotropy in energy density profiles from high-energy collisions, revealing universal behaviors in small systems and dependence on initial conditions in large systems.

Contribution

It generalizes eccentricity cumulant expressions to arbitrary fluctuating initial density profiles, highlighting the universal nature of non-Gaussianities in small collision systems.

Findings

Anisotropy harmonic fluctuations are inherently non-Gaussian.

Universal non-Gaussian features are present in small systems like p+Pb.

Eccentricity cumulants are generalized for arbitrary initial density fluctuations.

Abstract

We study the fluctuations of the anisotropy of the energy density profile created in a high-energy collision at the LHC. We show that the anisotropy in harmonic $n$ has generic non-Gaussian fluctuations. We argue that these non-Gaussianities have a universal character for small systems such as p+Pb collisions, but not for large systems such as Pb+Pb collisions where they depend on the underlying non-Gaussian statistics of the initial density profile. We generalize expressions for the eccentricity cumulants $\varepsilon_2\{4\}$ and $\varepsilon_3\{4\}$ previously obtained within the independent-source model to a general fluctuating initial density profile.