Measurement of prompt $\mathrm{D}^0$ and $\overline{\mathrm{D}}^0$ meson azimuthal asymmetry and search for strong electric fields in PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

TL;DR

This study measures the azimuthal asymmetry of prompt D0 mesons in PbPb collisions at 5.02 TeV to investigate the presence of strong electric fields and analyzes flow coefficients to understand collision geometry effects.

Contribution

First measurement of the rapidity-dependent difference in elliptic flow between D0 and anti-D0 mesons in heavy ion collisions.

Findings

No significant rapidity-dependent difference in $v_2$ observed.

D0 meson $v_2$ shows a strong centrality dependence.

D0 and anti-D0 $v_3$ are largely independent of centrality.

Abstract

The strong Coulomb field created in ultrarelativistic heavy ion collisions is expected to produce a rapidity-dependent difference ($\Delta v_2$) in the second Fourier coefficient of the azimuthal distribution (elliptic flow, $v_2$) between $\mathrm{D}^0$ ($\mathrm{\bar{u}c}$) and $\overline{\mathrm{D}}^0$ ($\mathrm{u\bar{c}}$) mesons. Motivated by the search for evidence of this field, the CMS detector at the LHC is used to perform the first measurement of $\Delta v_2$. The rapidity-averaged value is found to be $\langle\Delta v_2 \rangle =$ 0.001 $\pm$ 0.001 (stat) $\pm$ 0.003 (syst) in PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV. In addition, the influence of the collision geometry is explored by measuring the $\mathrm{D}^0$ and $\overline{\mathrm{D}}^0$ mesons $v_2$ and triangular flow coefficient ($v_3$) as functions of rapidity, transverse momentum ($p_\mathrm{T}$), and event centrality (a measure of the overlap of the two Pb nuclei). A clear centrality dependence of prompt $\mathrm{D}^0$ meson $v_2$ values is observed, while the $v_3$ is largely independent of centrality. These trends are consistent with expectations of flow driven by the initial-state geometry.