Determine the electromagnetic transport coefficients governing charge-dependent directed flow

Determine the QGP drag parameter bc m and electrical conductivity c3 by comparing calculations of charge-dependent directed flow performed with realistic hydrodynamic backgrounds to experimental data, thereby reducing the principal transport-property uncertainties in the model.

Background

The model computes charge-dependent directed flow by combining spectator-induced electromagnetic fields with a perturbative drift velocity obtained from a force-balance equation. This calculation depends on the drag parameter bc m, which controls the response of charged fluid elements to electromagnetic forces, and on the electrical conductivity c3, which controls the time evolution of the electromagnetic fields in the conducting QGP.

The paper adopts phenomenological values for both quantities, while emphasizing that the drag prescription is being applied outside the setting in which it was originally derived. The authors therefore identify determining these transport properties through comparisons with experimental directed-flow data as an unresolved requirement for a quantitatively predictive framework.

References

Ultimately, the parameter \mu m in the force-balance equation eq:force_balance_section should be determined by comparing calculations of charge-dependent directed flow (like ours, but done with a realistic hydrodynamic background) to experimental data. At present, our lack of knowledge of the values of \mu m and the electrical conductivity \sigma (discussed in the previous Section) are two important sources of uncertainty in our modeling, as these are the two transport properties of QGP on which the charge-dependent directed flow that we calculate depends.

— The Interplay Between Electromagnetic Fields and Baryon Stopping in a Hydrodynamic Model for Charged Flow  (2609.17228 - Demircik et al., 15 Sep 2026) in Section VI, immediately following Eq. (19), “Computing Directed Flow Induced by Baryon Stopping and Electromagnetic Fields”