Elliptic flow of identified hadrons in small collisional systems measured with ALICE

TL;DR

This paper presents high-precision measurements of elliptic flow for various identified hadrons in p--Pb collisions at 5.02 TeV, providing insights into collective effects in small systems and testing theoretical models.

Contribution

It reports the first results for K_S^0, Lambda, and phi elliptic flow, and demonstrates mass ordering and scaling behaviors to constrain models of collective phenomena.

Findings

Observation of mass ordering in v2 among different hadrons

Evidence of approximate NCQ and KE_T scaling of v2

High-precision v2 measurements for multiple particle species

Abstract

Recent observations of long-range multi-particle azimuthal correlations in p--Pb and high multiplicity pp collisions provided new insights into collision dynamics and opened a possibility to study collective effects in these small systems. New measurement of $p_\mathrm{T}$-differential elliptic flow ($v_{2}$) coefficient for inclusive charged hadrons as well as a variety of identified particle species in p--Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV recorded by ALICE during the LHC Run 2 data taking are presented. Besides high precision measurements of $v_2(p_\mathrm{T})$ for $\mathrm{\pi^\pm, K^\pm}$ and $\mathrm{p(\bar{p})}$, the very first results for $\mathrm{K_{S}^{0}, \Lambda(\bar{\Lambda})}$ and $\phi$ are shown. In order to eliminate non-flow contamination, a pseudorapidity separation between correlated particles is applied as well as subtraction of remaining non-flow estimate based on a measurement of minimum-bias pp collisions at $\sqrt{s}=13$ TeV. Moreover, reported characteristic mass ordering and approximate NCQ and $\mathrm{KE_T}$ scaling of $v_{2}$ allows to test various theoretical models, constrain the initial conditions, and probe the origin of collective behavior in small collision systems.