Physicists have discovered new evidence that even small atomic collisions can create microscopic drops of matter that existed just after the Big Bang, according to research published January 15 in Physical Review Letters.
The findings come from analyzing data collected at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC), where scientists routinely create and study a peculiar state of matter called quark-gluon plasma by smashing gold ions together at extremely high energies.
“We found, for the first time in a small collision system, the suppression of energetic particles, which is one of two main pieces of evidence for the QGP,” said PHENIX Collaboration Spokesperson Yasuyuki Akiba, a physicist at Japan’s RIKEN Nishina Center for Accelerator-Based Science and Experiment Group Leader at the RIKEN-BNL Research Center at Brookhaven Lab.
The research challenges earlier assumptions about how much energy was needed to create this exotic form of matter. Scientists previously thought that collisions between small and large atomic nuclei wouldn’t generate enough energy to create quark-gluon plasma.
To understand what happens in these collisions, researchers looked for particles of light called direct photons. Unlike other particles, these photons pass through the collision debris unaffected, providing a clear window into the heart of the collision.
“If photons are created, they escape the QGP completely without any energy loss,” explained Axel Drees of Stony Brook University, one of the analysis leaders.
The team compared these photons to other particles that do interact with the plasma. Think of it like comparing something moving through air versus water – particles moving through the plasma slow down significantly, much like a runner would move more slowly through water than through air, as Gabor David of Stony Brook University explained.
The research could have implications for understanding how matter behaved in the earliest moments of the universe, when everything was compressed into an incredibly hot, dense state before expanding into the cosmos we see today.
The scientists used data from RHIC’s PHENIX detector, which operated from 2000 to 2016. Future analyses will look at different types of atomic collisions to further confirm these findings.
The research was funded by the U.S. Department of Energy Office of Science and the National Science Foundation, along with support from various universities and international organizations.