Impact of magnetic-field fluctuations on measurements of the chiral magnetic effect in collisions of isobaric nuclei

Abstract: We investigate the properties of electromagnetic fields in isobaric ${44}^{96}\textrm{Ru}+\,{44}^{96}\textrm{Ru}$ and ${40}^{96}\textrm{Zr}+\,{40}^{96}\textrm{Zr}$ collisions at $\sqrt{s}$ = 200 GeV by using a multiphase transport model, with special emphasis on the correlation between magnetic field direction and participant plane angle $\Psi_{2}$ (or spectator plane angle $\Psi_{2}^{\rm SP}$), i.e. $\langle{\rm cos}\ 2(\Psi_B - \Psi_{2})\rangle$ [or $\langle{\rm cos}\ 2(\Psi_B - \Psi_{2}^{\rm SP})\rangle$]. We confirm that the magnetic fields of ${44}^{96}\textrm{Ru}+\,{44}^{96}\textrm{Ru}$ collisions are stronger than those of ${40}^{96}\textrm{Zr}+\,{40}^{96}\textrm{Zr}$ collisions due to their larger proton fraction. We find that the deformation of nuclei has a non-negligible effect on $\langle{\rm cos}\ 2(\Psi_B - \Psi_{2})\rangle$ especially in peripheral events. Because the magnetic-field direction is more strongly correlated with $\Psi_{2}^{\rm SP}$ than with $\Psi_{2}$, the relative difference of the chiral magnetic effect observable with respect to $\Psi_{2}^{\rm SP}$ is expected to be able to reflect much cleaner information about the chiral magnetic effect with less influences of deformation.