Search for the Chiral Magnetic Wave with Anisotropic Flow of Identified Particles at RHIC-STAR

TL;DR

This study investigates the presence of the chiral magnetic wave (CMW) in heavy-ion collisions by analyzing flow patterns of identified particles, finding evidence supporting CMW as a plausible explanation over alternative mechanisms.

Contribution

The paper provides experimental measurements of flow asymmetries in identified particles, offering new evidence that supports the CMW interpretation at RHIC energies.

Findings

Flow asymmetry slopes are consistent with CMW predictions.

Hydrodynamics and local charge conservation are less likely to explain the results.

Small slopes in p+Au and d+Au collisions support the CMW hypothesis.

Abstract

The chiral magnetic wave (CMW) has been theorized to propagate in the Quark-Gluon Plasma formed in high-energy heavy-ion collisions. It could cause a finite electric quadrupole moment of the collision system, and may be observed as a dependence of elliptic flow, $v_{2}$, on the asymmetry between positively and negatively charged hadrons, $A_{\rm ch}$. However, non-CMW mechanisms, such as local charge conservation (LCC) and hydrodynamics with isospin effect, could also contribute to the experimental observations. Here we present the STAR measurements of elliptic flow $v_{2}$ and triangular flow $v_{3}$ of charged pions, along with $v_{2}$ of charged kaons and protons, as functions of $A_{\rm ch}$ in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. The slope parameters of $\Delta v_{2}$($A_{\rm ch}$) and $\Delta v_{3}$($A_{\rm ch}$) are reported and compared to investigate the LCC background. The similarity between pion and kaon slopes suggests that the hydrodynamics is not the dominant mechanism. The difference between the normalized $\Delta v_{2}$ and $\Delta v_{3}$ slopes, together with the small slopes in p+Au and d+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV, suggest that the CMW picture remains a viable interpretation at RHIC.