Charge asymmetry dependence of anisotropic flow in pPb and PbPb collisions with CMS experiment

Abstract

In nucleus-nucleus collisions, the linear dependence found for the elliptic flow harmonic of both positive or negative charged particles as a function of event charge asymmetry is predicted by the phenomenon known as the Chiral Magnetic Wave (CMW) due to its induced electric quadrupole moment. Here, the event charge asymmetry $A_{\mathrm{ch}}$ is defined as $\frac{N_{+}-N_{-}}{N_{+}+N_{-}}$, where $N_{+}$ and $N_{-}$ are the number of positive and negative charged particles, respectively. However, other scenarios are also possible and may provide alternative explanations for the experimental results. New measurements of elliptic ($v_2$) and triangular ($v_3$) flow for positive and negative charged particles as a function of $A_{\mathrm{ch}}$ in pPb and PbPb collisions at $\sqrt{s_{{}_{NN}}}=5.02\mathrm{TeV}$ are presented, using data collected by the CMS experiment during the LHC runs 1 and 2. The slopes and intercepts of the charged-dependent $v_n$ harmonics vs. $A_{\mathrm{ch}}$ are directly compared for pPb and PbPb collisions with similar charged-particle multiplicities, where a strong CMW effect is not expected in very high multiplicity pPb events. Moreover, a comparison is made of the slope parameters between $v_2$ and $v_3$ harmonics normalized by the inclusive charge particle $v_n$ in PbPb collisions as a function of centrality. These results provide a means to discriminate between the CMW and other scenarios such as local charge conservation as possible explanations for the observed charge dependent behavior.

5 pages, 3 figures, proceedings for XXVIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2017)

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