Charge asymmetry dependence of anisotropic flow in pPb and PbPb collisions with the 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 Ach is defined as 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 (v2) and triangular (v3) flow for positive and negative charged particles as a function of Ach in pPb and PbPb collisions at sNN=5.02 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 vn harmonics vs. Ach 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 v2 and v3 harmonics normalized by the inclusive charge particle vn 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.