# New results on collectivity with ATLAS

## TL;DR

This paper presents recent ATLAS measurements of collective phenomena across various collision systems, revealing insights into particle emission sources, flow characteristics, and fluctuations in high-energy nuclear collisions.

## Contribution

It provides new experimental results on collectivity in small and large collision systems, including HBT measurements, flow analysis, and fluctuation studies, expanding understanding of collective effects.

## Key findings

- Particle emission source measured via HBT in p+Pb collisions
- Elliptic flow of charged hadrons and muons analyzed in p+Pb
- Longitudinal flow fluctuations studied in Pb+Pb collisions

## Abstract

The collective phenomena are observed not only in heavy ion collisions, but also in the proton-nucleus and in high-multiplicity $pp$ collisions. The latest results from this area obtained in ATLAS are presented. In $p$+Pb collisions the emission source of particles is measured using the HBT method. The analysis of $p$+Pb data collected in 2016 provides information on the elliptic flow of charged hadrons and muons. Low multiplicity events from $pp$, $p$+Pb and peripheral Pb+Pb collisions are studied with the cumulant methods. A deeper understanding of Pb+Pb collisions is provided by the analysis of longitudinal fluctuations of the collective flow parameters.