Search for strong electric fields in PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV using azimuthal anisotropy of prompt $\mathrm{D}^0$ and $\overline{\mathrm{D}}^0$ mesons

The CMS collaboration
Sirunyan, Albert M , Tumasyan, Armen , Adam, Wolfgang , Ambrogi, Federico , Bergauer, Thomas , Dragicevic, Marko , Erö, Janos , Escalante Del Valle, Alberto , Fruehwirth, Rudolf , Jeitler, Manfred
Phys.Lett.B 816 (2021) 136253, 2021.

Abstract (data 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 $D^0$ ($\overline{u}c$) and $\overline{D}^0$ ($u\overline{c}$) 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 $<\Delta v_2>=0.001\pm0.001(stat)\pm0.003(syst)$ in PbPb collisions at $\sqrt{s_{NN}}=5.02~TeV$. In addition, the influence of the collision geometry is explored by measuring the $D^0$ and $\overline{D}^0$ mesons $v_2$ and triangular flow coefficient ($v_3$) 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 $D^0$ 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.

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