“We want to understand the properties of QGP,” said nuclear theorist Raju Venugopalan, one of the authors on the new paper. “We don’t know how those properties might be used, but 100 years ago, we didn’t know how we’d use the collective properties of electrons, which now form the basis of almost all of our technologies. Back then, electrons were just as exotic as the quarks and gluons are now.”
|The STAR collaboration’s exploration of the “nuclear phase diagram” shows signs of a sharp border–a first-order phase transition–between the hadrons that make up ordinary atomic nuclei and the quark-gluon plasma (QGP) of the early universe when the QGP is produced at relatively low energies/temperatures. The data may also suggest a possible critical point, where the type of transition changes from the abrupt, first-order kind to a continuous crossover at higher energies.
Credit: Image courtesy of Brookhaven National Laboratory
At this so-called “critical point,” there would be a toll stop, but the cost would be $0, so the quarks and gluons could transition from protons and neutrons to QGP very quickly — almost as if all the water in the pot turned to steam in a single instant. This can actually happen when water reaches its boiling point under high pressure, where the distinction between the liquid and the compressed gas phases blurs to the point of the two being virtually indistinguishable. In the case of QGP, the physicists would expect to see signs of this dramatic effect — patterns in the fluctuations of particles observed striking their detectors — the closer and closer they get to this critical point.
Signposts to look for
“All the predictions, the way we started looking for a critical point so far, were based on patterns calculated assuming you have a pot boiling on a stove – a somewhat static system,” said Mukherjee. “But QGP is expanding and changing over time. It’s more like water boiling as it flows rapidly through a pipe.”
“These ideas have since been applied to other systems like liquid helium and liquid crystals,” Venugopalan said. “Yin realized that the specific mechanisms of dynamic universality identified in cosmology and condensed matter systems can be applied to the search for the critical point in heavy ion collisions. This paper is the first explicit demonstration of this conjecture.”
“If the STAR collaboration looks at the data in a particular way and sees these patterns, they can claim without any ambiguity that they have seen a critical point,” Venugopalan said.