Abstract
Based on a holographic far-from-equilibrium calculation of the chiral magnetic effect~(CME) in an expanding quark gluon plasma, we study collisions at various energies. We compute the time evolution of the CME current in the presence of a time-dependent axial charge density and subject to a time-dependent magnetic field. The plasma expansion leads to a dilution of the CME current. We study distinct combinations of how the initial magnetic field and initial axial charge behave with changing initial energy as proposed in previous literature. Most scenarios we consider lead to an increasing time-integrated CME current, when increasing the initial energy. This would make it more likely to observe the CME at higher collision energies.
Highlights
Significant experimental effort has been directed at the observation of the chiral magnetic effect (CME), which refers to the separation of electromagnetic charges along a magnetic field B [1–8], a signal of the presence of the chiral anomaly [9,10]
We begin by showing that the time evolution of the energy density, pressure, and CME current is largely independent of the choices of profiles in the AdS radial direction at the initial time
In this work we reported on the beam energy dependence of the chiral magnetic effect in an expanding quark gluon plasma (QGP) based on a holographic model, initially far from equilibrium
Summary
Significant experimental effort has been directed at the observation of the chiral magnetic effect (CME), which refers to the separation of electromagnetic charges along a magnetic field B [1–8], a signal of the presence of the chiral anomaly [9,10]. The charge distribution inside the nuclei will affect the magnetic field generated by the colliding ions This constitutes another known uncertainty: the magnitude, spatial extent, and time evolution of the magnetic field over the lifetime of the plasma, for which there exist many different (sometimes contradictory) predictions [39–46]. [48] to include the effect of the expansion of the plasma, include the time dependence for the axial charge density and magnetic field, start with an initial state anisotropic in the transverse plane, and consider the pressure anisotropies as observables. In terms of the time evolution of the plasma, the axial charge and the magnetic field, our model plasma extends this nonexpanding case [48] as well as the (ideal) magnetohydrodynamics Bjorken-expanding case, which is discussed in Ref. Appendix C briefly details the numerical methods we use to solve the time-dependent Einstein equations
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