Baryon electric charge correlation as QCD magnetometer

Key Laboratory of Quark and Lepton Physics (MOE) and Institute of Particle Physics, Central China Normal University, Wuhan 430079, China

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Published online: 17 April 2026

Abstract

The detection of strong magnetic fields in peripheral heavy-ion collisions is crucial for observing effects such as the chiral magnetic effect but has proven exceptionally difficult. To address this, we propose the baryon electric charge correlation χ₁₁^BQ and the chemical potential ratio μ_q/μ_b as sensitive probes of magnetic fields, based on (2+1)-flavor lattice QCD simulations at the physical pion mass. Along the transition line, χ₁₁^BQ and (μ_q/μ_b)_lo in Pb-Pb collisions increase by factors of 2.1 and 2.4 at eB ≃ 8MM_π², respectively. To bridge theoretical predictions with experimental observables, we implement systematic kinematic cuts that emulate detector acceptances of the STAR and ALICE experiments within the hadron resonance gas model. This allows us to construct experimentally relevant proxy observables. Furthermore, we demonstrate that (μ_q/μ_b)_lo is also sensitive to the collision system, showing a 1.5-fold increase from Zr-Zr to Ru-Ru isobar collisions. Our findings offer new insights into thermo-magnetic effects and provide experimentally relevant guidance for the detection of magnetic fields in heavy-ion collisions.