In collisions of heavy nuclei at colliders, quark-gluon plasma is born — a state of matter where quarks and gluons are as free as water in steam. Heavy quarks, such as b-quarks, entering this plasma lose energy, and their bound states, bottomonia, are destroyed. By how much rarer they are produced compared to expectations without plasma, one can infer the properties of the medium.
The authors used a neural network to reconstruct the interaction potential between a heavy quark and an antiquark inside the plasma from experimental data. This potential has real and imaginary parts: the real part accounts for the attractive force, the imaginary part for absorption of particles by the medium. The neural network was trained on thousands of potential variants, and then, using a Bayesian approach, extracted the most likely parameters from LHC and RHIC data.
The result showed that the real part of the potential barely changes with collision energy, remaining close to its vacuum form, while the imaginary part grows with temperature. This means that in going from RHIC to LHC, the hot medium becomes more absorbing, although the attractive force between quarks changes little.
Quark-gluon plasma is the hottest liquid ever created by humans: its temperature is thousands of times higher than the temperature of the Sun's core.
The idea of 'quark matter' appears in Greg Egan's novel 'Quarantine': there, neuromods allow control over quantum states, which vaguely resembles manipulations with quark potentials.