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 $Ψ_{2}$ (or spectator plane angle $Ψ_{2}^{\rm SP}$), i.e. $\langle{\rm cos}\ 2(Ψ_B - Ψ_{2})\rangle$ [or $\langle{\rm cos}\ 2(Ψ_B - Ψ_{2}^{\rm SP})\rangle$]. 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 $\langle{\rm cos}\ 2(Ψ_B - Ψ_{2})\rangle$ especially in peripheral events. Because the magnetic-field direction is more strongly correlated with $Ψ_{2}^{\rm SP}$ than with $Ψ_{2}$, the relative difference of the chiral magnetic effect observable with respect to $Ψ_{2}^{\rm SP}$ is expected to be able to reflect much cleaner information about the chiral magnetic effect with less influences of deformation.