Oxygen collisions show evidence of jet quenching, a signature of early-universe matter

New findings from the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) suggest that colliding oxygen nuclei at near-light speeds produce quark-gluon plasma (QGP), a type of matter that existed shortly after the Big Bang. The data, published in Physical Review Letters, reveals that energetic particle jets lose energy as they pass through the hot, dense matter generated by the collisions.

This phenomenon, known as jet quenching, has been observed in both oxygen-oxygen and gold-gold collisions at RHIC. The analysis at lower collision energies establishes a new minimum energy requirement for producing the primordial QGP in such small systems. Professor Li Yi, overseeing the STAR analysis, emphasizes the importance of understanding QGP's properties to unravel the early universe's evolution during its first microseconds.

STAR physicist Rongrong Ma adds that the study pushes the boundaries of knowledge about jet quenching and the conditions required to generate a QGP. The RHIC's gold nucleus collisions, consisting of 79 protons and 118 neutrons, effectively melt atomic nuclei to release quarks and gluons. The resulting QGP is too small and short-lived to be directly observed, so scientists study the energy loss of particles emerging from the collisions to infer its presence.

Oxygen collisions provide a smaller, symmetric system that could help identify the smallest system in which jet quenching signals are unambiguous, aiding in the search for QGP formation.