Hydrodynamics of Relativistic Heavy-Ion Collisions
Summary
When nuclei collide at ultrarelativistic energies, they create a hot, dense medium of deconfined quarks and gluons known as the quark–gluon plasma. This medium behaves collectively and can be described with relativistic hydrodynamics, treating it as a near-ideal fluid whose expansion is governed by conservation laws and the properties of its equation of state. Initial spatial asymmetries in the overlap region translate into anisotropic pressure gradients, driving anisotropic flow patterns in the final-state particle distributions. Modern approaches incorporate both ideal and viscous terms, accounting for shear and bulk viscosity, and often employ second-order formulations to ensure causality and stability. Numerical simulations couple these hydrodynamic equations to models of the early pre-equilibrium stage and to hadronic rescattering at freeze-out, enabling detailed comparisons with measurements of collective flow coefficients, particle spectra and correlations. This framework has deepened our understanding of the transport properties of strongly interacting matter under extreme conditions and of the fundamental degrees of freedom in quantum chromodynamics.
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Hydrodynamics of Relativistic Heavy-Ion Collisions publication trend
The graph below shows the total number of articles in hydrodynamics of relativistic heavy-ion collisions across all publications each year (not limited to Nature Index journals).
Technical terms
Quark–gluon plasma: A deconfined state of matter consisting of free quarks and gluons formed at extreme temperature and density.
Hydrodynamic flow: Collective expansion of the created medium driven by pressure gradients, characterised by anisotropic flow coefficients.
Shear viscosity: A measure of a fluid’s resistance to transverse momentum transport, influencing the smoothing of velocity gradients.
Equation of state: The relation between pressure, energy density and temperature that determines the medium’s response to expansion.
References
- Extracting the speed of sound in quark–gluon plasma with ultrarelativistic lead–lead collisions at the LHC. Reports on Progress in Physics (2024).
- Observation of the Electromagnetic Field Effect via Charge-Dependent Directed Flow in Heavy-Ion Collisions at the Relativistic Heavy Ion Collider. Physical Review X (2024).
- Determination of the Neutron Skin of Pb208 from Ultrarelativistic Nuclear Collisions. Physical Review Letters (2023).
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