Search for the Chiral Magnetic Wave in Pb--Pb collisions using the ALICE detector

TL;DR

This study investigates the presence of the Chiral Magnetic Wave in heavy-ion collisions by analyzing charge-dependent flow measurements, employing novel event-shape engineering to distinguish potential signals from background effects.

Contribution

The paper introduces the first application of event-shape engineering to separate CMW signals from background in Pb--Pb collision data.

Findings

Background effects dominate the measurements

No conclusive evidence of the CMW signal

Charge asymmetry dependence mainly due to background

Abstract

The interplay of the chiral anomaly and the strong magnetic field ($\sim$ 10$^{15}$ T) created in heavy-ion collisions could give rise to a collective excitation in the quark--gluon plasma called the Chiral Magnetic Wave (CMW). This effect can be experimentally sought by the charge asymmetry ($A_{\rm ch}$) dependence of elliptic flow $v_{2}$. However, non-CMW mechanisms such as local charge conservation (LCC) coupled with collective flow can also lead to a similar dependence of $v_{2}$ on $A_{\rm ch}$. The triangular flow ($v_{3}$) measurement serves as a reference as it is not expected to be affected by the CMW. The $v_{2}$ and $v_{3}$ of charged hadrons as a function of $A_{\rm ch}$ measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 and 5.02 TeV are presented. In addition, the event-shape engineering (ESE) technique is adopted for the first time to quantitatively disentangle the CMW signal and the LCC background. The results indicate that the background effects dominate the CMW measurements.