Scientists take a closer look at the inside of the perfect fluid

Scientists have reported new clues to solve a cosmic riddle: how quark-gluon plasma, nature’s perfect fluid, turned into matter.

A few millionths of a second after the Big Bang, the early universe took on a strange new state: a subatomic soup called quark-gluon plasma.

And just 15 years ago, an international team including researchers from the Relativistic Nuclear Collisions (RNC) group at the Lawrence Berkeley National Laboratory (Berkeley Lab) discovered that this quark-gluon plasma is a perfect fluid – in which quarks and gluons, the building blocks of protons and neutrons, are so strongly coupled that they flow almost without friction.

Scientists have postulated that jets of highly energetic particles pass through quark-gluon plasma, a droplet the size of an atom’s nucleus, at speeds faster than the speed of sound and that, like a rapid jet, emit a supersonic boom called Mach. wave. To study the properties of these jet particles, in 2014 a team led by scientists at the Berkeley Lab pioneered an atomic x-ray imaging technique called jet tomography. The results of these fundamental studies revealed that these jets disperse and lose energy as they propagate through quark-gluon plasma.

But where did the journey of jet particles in quark-gluon plasma begin? A smaller Mach wave signal called a scattering wake, scientists predicted, would tell you where to look. But while the energy loss was easy to observe, the Mach wave and accompanying scattering wake remained elusive.

Now, in a study published recently in the journal Physical examination letters, scientists at the Berkeley Lab report new results from model simulations showing that another technique they invented, called 2D jet tomography, can help researchers locate the ghostly signal in the scattering wake.

“Its signal is so small, it’s like looking for a needle in a haystack of 10,000 particles. For the first time, our simulations show that we can use 2D jet tomography to pick up the tiny signals in the wake. diffusion in quark-gluon plasma, “said study leader Xin-Nian Wang, a senior scientist in the nuclear sciences division of the Berkeley Lab who was part of the international team that invented the tomography technique by 2D jet.

To find this supersonic needle in the quark-gluon haystack, the Berkeley Lab team analyzed hundreds of thousands of lead-nucleus collision events simulated at CERN’s Large Hadron Collider (LHC), and collision events. gold-nucleus at the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory. Some of the computer simulations in this study were performed at the Berkeley Lab NERSC supercomputer user facility.

Wang says their unique approach “will help you get rid of all that hay in your pile, help you focus on that needle.” The supersonic signal from the jet particles has a unique cone-like shape, with a scattering wake behind, like ripples of water in the wake of a fast moving boat. Scientists have been looking for evidence of this supersonic “wakelet” because it tells you that there is particle depletion. Once the scattering wake is located in the quark-gluon plasma, you can distinguish its signal from other particles in the background.

Their work will also help LHC and RHIC experimenters understand what signals to look for in their quest to understand how quark-gluon plasma, nature’s perfect fluid, turned into matter. “What are we made of? What was the infant universe like in the few microseconds after the Big Bang? It’s still a work in progress, but our much sought-after scattering wake simulations bring us closer to the answer to these questions, ”he added. he said.