Event Shape Engineering in Search of the Chiral Magnetic Effect in Heavy-ion Collisions

In high-energy heavy-ion collisions, the deconfined quark-gluon plasma could manifest a spontaneous electric-charge separation in the direction of a strong magnetic field through the chiral magnetic effect (CME). Experimentally, the γ₁₁₂ ≡ 1 + φ₂ - 2Ψ_RP)> correlator measures the charge separation between two particles across the reaction plane, and is the main observable in search of the CME. However, the recent isobar blind analysis by the STAR Collaboration did not observe any pre-defined CME signal [1], indicating that the γ₁₁₂ results are dominated by the flow-related background. We present a method study of event-shape engineering (ESE) that projects γ₁₁₂ and its pure-background variation (γ₁₃₂ ≡ 1 - 3φ₂ + 2Ψ_RP)>) for π-π correlations to a class of events with minimal flow. We explore multiple event-shape variables to realize the zero-flow mode. The sensitivity on the CME signal and the background are studied for Au+Au, Ru+Ru, and Zr+Zr collisions at √s_NN = 200 GeV with a multiphase transport (AMPT) model, as well as a new event generator, Event-By-Event Anomalous-Viscous Fluid Dynamics (EBE-AVFD).

[1] M. Abdallah et al. (STAR Collaboration), Phys. Rev. C 105, 014901 (2022).