Speaker
Description
The interplay of the chiral anomaly and the strong magnetic field (~10$^{15}$ T) created in the off-central heavy-ion collisions could give rise to a collective excitation in the quark-gluon plasma called the Chiral Magnetic Wave (CMW), which can be experimentally sought by the charge asymmetry ($A_{\rm ch}$) dependence of elliptic flow $v_2$ of positively and negatively charged hadrons. However, non-CMW mechanisms such as local charge conservation (LCC) intertwined with collective flow can also lead to a similar dependence of $v_2$ on $A_{\rm ch}$. The measurement with triangular flow ($v_3$) thus serves as a reference as it is not expected to be affected by the CMW.
In this talk, we present new ALICE measurements of $v_2$ and $v_3$ of inclusive and identified hadrons as functions of $A_{\rm ch}$ in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 and 5.02 TeV. The slope parameters of $\Delta v_2$-$A_{\rm ch}$ and $\Delta v_3$-$A_{\rm ch}$ correlations, where the $\Delta v_n$ are the differences between $v_n$ of positive and negative particles, are normalized and then compared with results from other experiments and models. In addition, the Event Shape Engineering (ESE) technique is adopted for the first time to quantitatively distinguish the CMW signal and the LCC background. The upper limit of the CMW signal contribution is further extracted. Our measurements reveal that the background effect is dominant in the search for the CMW in heavy-ion collisions.
