A team of scientists is exploring the critical point in the phase diagram of quantum chromodynamics using particle accelerators and new simulations. Their goal is to directly observe the transition between quark-gluon plasmas and hadronic phases, enhanced by theoretical and experimental advances from the Beam Energy Scan program.
the transition between quark and gluon plasma
A team of researchers is conducting experiments looking for evidence of a possible critical point in the phase diagram of the quantum chromodynamics (QCD). Quantum chromodynamics describes how the strong force binds quarks and antiquarks together to form protons, neutrons, and other particles known as hadrons. The critical point is similar to the endpoint of the liquid-to-gas transition in ordinary water.
Key indicators of this tipping point that scientists can observe are related to changes in the number of particles produced in particle accelerator collisions. Modeling these observables requires an extension of the standard framework of how liquids and gases behave. Scientists have now developed an algorithm to run simulations of a critical fluid and have tested those simulations.
The observation of the critical fluctuation in a heavy ion collision would mark the first direct observation of a phase change between the quark-gluon plasma and a hadronic phase. This is the point where quarks and gluons are confined to hadrons. Interpreting the results of related experiments requires new theoretical tools.
In particular, the interpretation requires a fluid dynamic framework that incorporates fluctuations, or how pressure, velocity and other factors can change in liquids and gases. This work is an important contribution to this effort. In the future, the researchers hope to use these methods to link the data with theoretical ideas about the nature of temperature and pressure in quark-gluon matter.
The Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider, a Department of Energy user facility at Brookhaven National Laboratory, studies the energy dependence of fluctuation observables in heavy ion collisions. The objective of this study is to identify a possible critical point associated with the phase transition towards a quark-gluon plasma.
Interpretation of BES program results requires a fluid dynamics framework that incorporates fluctuations in the fluid dynamics variables, baryon density, entropy density, and fluid velocity.
In this research, scientists built such a framework and tested it in the simulation of a static fluid near the critical point. Future work will associate their results with the expansion of the fireball created in a heavy ion collision. This will allow researchers to locate the critical point or place constraints on its location.
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