Probing the transverse size of initial inhomogeneities with flow observables

TL;DR

This paper investigates how initial inhomogeneities' size affects flow observables in heavy ion collisions, finding some observables insensitive to granularity while others can probe short-scale initial density features.

Contribution

The paper introduces a method to vary initial inhomogeneity size while keeping global properties fixed, and identifies sensitive observables for initial granularity.

Findings

Many flow observables are insensitive to hot spot sizes.

Factorization breaking ratio rn is sensitive to initial granularity.

Sub-leading PCA components can probe short-scale initial density features.

Abstract

Disentangling the effect of initial conditions and medium properties is an open question in the field of relativistic heavy ion collisions. We argue that, while one can study the impact of initial inhomogeneities by varying their size, it is important to maintain the global properties fixed. We present a method to do this. We show that many observables are insensitive to the the hot spot sizes, including integrated vn, scaled distributions of vn, symmetric cumulants, eventplane correlations, and differential vn(pT ). We find however that the factorization breaking ratio rn and sub-leading component in a Principal Component Analysis are more sensitive to the initial granularity and can be used to probe short-scale features of the initial density.