Berkeley Lab reported that new simulations of quark-gluon plasma reveal extreme acceleration building up along the edges of the universe's hottest fluid. Physicists Yu-Gang Ma and Xu-Guang Huang from Fudan University led the research team, mapping how acceleration forms and changes inside the plasma across collision energies ranging from 3.5 GeV to 2.76 TeV.
Quark-gluon plasma forms when atomic nuclei smash together at nearly the speed of light, briefly creating a state where quarks and gluons move freely. While past studies focused on the fluid's intense swirling motion and electromagnetic fields, researchers have given less scrutiny to its acceleration. In hydrodynamics, acceleration is treated as equally fundamental as vorticity.
To examine the material as an evolving fluid, the team combined the AMPT and UrQMD particle transport models with a Gaussian smearing method. This technique converted particle distributions into continuous fields of energy, momentum, and velocity. The simulations showed that peak proper acceleration can reach several hundred MeV at both low and high collision energies, with the strongest transverse acceleration consistently pointing outward near the outer boundary of the fireball.
Plasma Dynamics
According to the relativistic Euler equation, the outer boundary becomes an acceleration hotspot because pressure drops rapidly while enthalpy density stays low. At lower collision energies, nuclear stopping slows the matter down, creating deceleration up to about 500 MeV. At ultrarelativistic energies, nuclei pass through each other quickly and pull newly created plasma into brief acceleration pulses.
The team noted that because the strongest acceleration remains along the boundary, the overall effect changes only slightly whether nuclei collide head-on or strike each other at an angle. Professor Huang explained that acceleration is not merely a kinematic detail, but may act as a thermodynamic control parameter for quantum chromodynamics (QCD) matter.
Quantum Effects
Acceleration could alter the thermodynamic phase structure of QCD matter through the Unruh effect, where an accelerating observer perceives empty space as thermal. An acceleration of several hundred MeV resembles temperatures close to the QCD transition temperature, potentially adding a new acceleration axis to the phase diagram that affects chiral transition and quark confinement.
Acceleration may also generate unexplored transport effects and influence particle spin alignments, complementing vorticity effects seen at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). The researchers plan to incorporate more realistic hydrodynamic evolution into future calculations and search for measurable signals in hyperon spin polarization patterns. Their findings were published in Nuclear Science and Techniques on August 3, 2026.
