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.
Highlights
Lattice QCD calculations predicted that quarks and gluons are deconfined with their partonic degrees of freedom under the condition of high temperatures or the high baryon chemical potential, i.e., the formation of quark-gluon plasma (QGP)
A nonzero axial charge density of the QGP with a large magnetic-field B can lead to a dipole charge separation along the B direction, i.e., the so-called chiral magnetic effect (CME), which results in a generation of a vector current J [1,2,3,4,5], J = σ5B, σ5
II, we provide a brief introduction to the a multiphase transport model (AMPT) model, our isobaric deformation settings, and the method to calculate magnetic fields
Summary
Lattice QCD calculations predicted that quarks and gluons are deconfined with their partonic degrees of freedom under the condition of high temperatures or the high baryon chemical potential, i.e., the formation of quark-gluon plasma (QGP). To measure the CME signal, people usually measure charge azimuthal correlation [6,7,8] between two particles α and β, which is defined as γ = cos(φα + φβ − 2 RP ) ,. The same nucleon number indicates they should have similar bulk backgrounds (e.g., flow), the different proton number means they carry different magnitudes of magnetic fields. If there are similar or even the same backgrounds in two isobaric collisions, the difference of the CME observable between two isobaric collisions is expected to be mainly due to the differences from the squared magnetic field and the correlation between magnetic-field direction B and participant.
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