Energy and system-size dependence of the Chiral Magnetic Effect

TL;DR

This paper investigates how the Chiral Magnetic Effect varies with collision energy and system size in heavy-ion collisions, predicting a significant weakening at LHC energies and a sharp disappearance above SPS energies, emphasizing the need for targeted experiments.

Contribution

It introduces a phenomenological model for energy dependence of the CME and highlights the importance of new experiments at LHC and low-energy RHIC scans to explore this effect.

Findings

CME expected to be ~20 times weaker at LHC than at RHIC.

CME should sharply vanish above SPS energy levels.

The HSD transport model with electromagnetic fields aids in understanding CME backgrounds.

Abstract

The energy dependence of the local ${\cal P}$ and ${\cal CP}$ violation in Au+Au and Cu+Cu collisions in a large energy range is estimated within a simple phenomenological model. It is expected that at LHC the chiral magnetic effect will be about 20 times weaker than at RHIC. At lower energy range, covered by the low-energy scan at RHIC and future NICA/FAIR facilities, the created magnetic field strength and energy density of deconfined matter are rather high providing necessary conditions for the chiral magnetic effect. However, the particular model for the chiral magnetic effect predicts that this effect should vanish sharply at energy somewhere above the top SPS one. To elucidate CME background effects the Hadron-String-Dynamics (HSD) transport model including electromagnetic fields is put forward. Importance of new planning experiments at LHC and for the low-energy RHIC scan program is emphasized.