Conditions for zero ESS intercept without CME

Ascertain the combinations of event-content parameters—such as relative resonance abundances versus primordial pions, resonance elliptic anisotropies and transverse-momentum spectra, and primordial particle elliptic anisotropies and transverse-momentum spectra—that yield a zero Event-Shape Selection (ESS) intercept ΔγESS in the absence of any Chiral Magnetic Effect signal.

Background

Based on model studies, the authors find that the ESS intercept ΔγESS can be negative, zero, or positive depending on the detailed makeup of the event, including resonance mixtures and mass continuum contributions. This sensitivity complicates the interpretation of the v2=0 intercept as a clean CME signal.

They therefore highlight that identifying the event-content configurations that guarantee ΔγESS=0 in the absence of CME is currently unknown, which undermines the practicality of using ESS intercepts as robust CME indicators.

References

The issue is, unfortunately, that it is unknown, needless to say proven, what combinations of all those elements in the event would give the ideal $\dgess=0$ in the absence of CME.

— Investigating the Event-Shape Methods in Search for the Chiral Magnetic Effect in Relativistic Heavy Ion Collisions  (2407.14489 - Li et al., 2024) in Section "summary"