# Measuring Momentum-Dependent Flow Fluctuations in Heavy-Ion Collisions

## TL;DR

This paper introduces new PCA observables in heavy-ion collision analysis that effectively distinguish flow fluctuations from multiplicity fluctuations, offering deeper insights into the initial collision stages.

## Contribution

It proposes novel PCA observables that are resistant to multiplicity fluctuations, enabling clearer study of flow fluctuations in heavy-ion collisions.

## Key findings

- New PCA observables are robust against multiplicity fluctuations.
- These observables isolate novel flow fluctuation sources.
- Enhanced understanding of initial collision stages at small scales.

## Abstract

In heavy-ion collisions, momentum-dependent pair correlations can be characterized by a principal component analysis (PCA), in which subleading modes are expected to reveal new information on flow fluctuations. However, we find that, as currently measured, these modes can be dominated by multiplicity fluctuations, which serve as an unwanted background. Here, we propose new PCA observables that are robust against multiplicity fluctuations and isolate novel sources of flow fluctuations, thus being suited to provide fresh insight into the initial stages of the system at small length scales.