Hydrodynamics and the Detection of the QCD Axial Anomaly in Heavy Ion Collisions

TL;DR

This work investigates how the QCD axial anomaly modifies relativistic hydrodynamics in high-density matter created in heavy ion collisions and proposes a novel, charge-independent experimental signal. By incorporating anomaly-induced currents proportional to vorticity and external fields, the authors connect microscopic triangle anomalies to macroscopic axial charge distributions and predict enhanced production of spin-excited hadrons along the rotation axis in off-central collisions. Using the Glauber model to estimate early-time axial densities and discussing the dominant $E_\mu B^\mu$ source term, they outline a measurable observable involving Omega minus and Xi minus baryons, with centrality-dependent signatures that reflect the axial charge distribution. The analysis emphasizes that a full numerical solution of the hydrodynamic equations and a realistic freeze-out treatment are required to determine the magnitude, but the qualitative features—axial-charge concentration along the rotation axis and a characteristic centrality pattern—provide a concrete pathway to detect topological QCD effects in heavy ion collisions.

Abstract

We consider the experimental implications of the axial current triangle diagram anomaly in a hydrodynamic description of high density QCD. We propose a signal of an enhanced production of spin-excited hadrons in the direction of the rotation axis in off-central heavy ion collisions.