In the underground rings of the Large Hadron Collider, CERN physicists collided oxygen-16 and neon-20 nuclei at near-light speeds and produced the smallest droplet of quark-gluon plasma ever created in a laboratory.
This exotic form of matter existed in the Universe for only a few microseconds after the Big Bang, when the temperature was so high that protons and neutrons could not yet form, and quarks and gluons moved freely in a dense "soup."
It was previously thought that heavy nuclei such as lead or xenon were needed to reproduce such a state, but new experiments have shown that even light nuclei, whose mass is less than a tenth that of lead, are capable of generating plasma that for a fraction of a second behaves like a liquid and expands collectively.
The ATLAS collaboration recorded the characteristic "jet quenching" — high-energy quarks lost a significant portion of their energy while passing through the medium, which manifested itself in an asymmetry of the particles' transverse momenta and served as direct proof of plasma formation.
Scientists from the Niels Bohr Institute reconstructed the original shape of the nuclei from the pattern of particle scattering: oxygen nuclei turned out to be almost spherical, while neon nuclei were asymmetric, resembling a cone or a bowling pin, like the shadow of an invisible object.
The method opens a new way to study the structure of nuclei and the strong interaction at extreme energies, and future collisions with even lighter nuclei, such as helium-4, will help determine the exact lower threshold at which quark-gluon plasma can arise.
Understanding these tiny "little bangs" brings us closer to unraveling how all the visible matter of stars, planets and living organisms emerged from the primordial plasma.
