Measurement of prompt D⁰ and D‾⁰ meson azimuthal anisotropy and search for strong electric fields in PbPb collisions at s _NN =5.02TeV

The strong Coulomb field created in ultrarelativistic heavy ion collisions is expected to produce a rapidity-dependent difference (Δv₂) in the second Fourier coefficient of the azimuthal distribution (elliptic flow, v₂) between D⁰ (u‾c) and D‾⁰ (uc‾) mesons. Motivated by the search for evidence of this field, the CMS detector at the LHC is used to perform the first measurement of Δv₂. The rapidity-averaged value is found to be 〈Δv₂〉=0.001±0.001(stat)±0.003(syst) in PbPb collisions at s _NN =5.02TeV. In addition, the influence of the collision geometry is explored by measuring the D⁰ and D‾⁰mesons v₂ and triangular flow coefficient (v₃) as functions of rapidity, transverse momentum (p_T), and event centrality (a measure of the overlap of the two Pb nuclei). A clear centrality dependence of prompt D⁰ meson v₂ values is observed, while the v₃ is largely independent of centrality. These trends are consistent with expectations of flow driven by the initial-state geometry.