Probing the chiral magnetic wave in p Pb and PbPb collisions at √ s NN = 5.02 TeV using charge-dependent azimuthal anisotropies

Abstract

Charge-dependent anisotropy Fourier coefficients ( v n ) of particle azimuthal distributions are measured in p Pb and PbPb collisions at √ s NN = 5.02 TeV with the CMS detector at the LHC. The normalized difference in the second-order anisotropy coefficients ( v 2 ) between positively and negatively charged particles is found to depend linearly on the observed event charge asymmetry with comparable slopes for both p Pb and PbPb collisions over a wide range of charged particle multiplicity. In PbPb , the third-order anisotropy coefficient v 3 shows a similar linear dependence with the same slope as seen for v 2 . The observed similarities between the v 2 slopes for p Pb and PbPb , as well as the similar slopes for v 2 and v 3 in PbPb , are compatible with expectations based on local charge conservation in the decay of clusters or resonances, and constitute a challenge to the hypothesis that, at LHC energies, the observed charge asymmetry dependence of v 2 in heavy ion collisions arises from a chiral magnetic wave.