Friction terms in multi-fluid description of heavy-ion collisions

TL;DR

This paper compares various methods for deriving friction terms in multi-fluid models of heavy-ion collisions, introduces a new charge transfer friction, and demonstrates its advantages through implementation in the MUFFIN model with initial viscous dynamics results.

Contribution

It introduces a new charge transfer friction approach, compares it with existing methods, and implements viscous multi-fluid dynamics in the MUFFIN model.

Findings

Charge transfer friction aligns better with three-fluid momentum separation.

Viscous multi-fluid dynamics can be integrated into the model.

New friction approach improves data and equation of state comparisons.

Abstract

In multi-fluid description of heavy-ion collisions, the primary scatterings and particle production are described in terms of interaction between fluids, so called friction. These friction terms can be derived from kinetic theory, but they are not unique. We compare different approaches to derive the friction terms, introduce a new ``charge transfer" friction, which allows to move charge to the midrapidity fireball, and implement them in the MUFFIN model. The charge transfer friction is more consistent with the assumption of three fluids clearly separated in momentum space, and allows better comparisons of the experimental data and underlying equation of state. It also leaves room for entropy generation due to dissipation in individual fluids, and we present the first results obtained using viscous multi-fluid dynamics.