Rapidity-dependent eccentricity scaling in relativistic heavy-ion collisions

TL;DR

This paper extends the understanding of initial spatial asymmetries and their influence on momentum anisotropy in heavy-ion collisions to three dimensions, analyzing rapidity dependence and response coefficients.

Contribution

It introduces rapidity-dependent eccentricities and systematically improves initial-state estimators for 3D heavy-ion collision modeling.

Findings

Rapidity-dependent eccentricities effectively describe 3D collision asymmetries.

Response coefficients vary with shear viscosity and total energy.

Extended eccentricity scaling applies beyond mid-rapidity regions.

Abstract

There is a well-established relation between the spatial asymmetry in the initial stage of a heavy-ion collision and the final momentum anisotropy, which allows for a separation of effects from initial conditions vs. later evolution and has proved exceptionally powerful. However, until recently it has only been studied in two dimensions -- either through boost-invariant simulations or studying only quantities at mid-rapidity. We explore an extension to 3 dimensions, in order to determine whether a similar understanding can be obtained for the rapidity dependence of the collision system. In particular, we introduce rapidity-dependent eccentricities and investigate a trivial extension of the 2D eccentricity scaling of elliptic and triangular flow, as well as a way to systematically improve these initial-state estimators. We then explore the dependence of the resulting response coefficients on shear viscosity and initial total energy.