Suffolk Reporter

A recent analysis from the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has provided new evidence suggesting that even small nuclei collisions with larger ones may create tiny drops of quark-gluon plasma (QGP). This substance, consisting of free quarks and gluons—the fundamental components of protons and neutrons—is believed to have filled the universe shortly after the Big Bang.

At RHIC, gold ions are collided energetically to create QGP by "melting" these nuclear building blocks, allowing scientists to study its properties. Initially, physicists thought smaller ion collisions wouldn't generate enough energy to form a QGP. However, findings from PHENIX have indicated that such small collision systems produce particle flow patterns consistent with QGP formation.

Published in Physical Review Letters, the latest results provide direct evidence that energetic particles in RHIC's small collision systems can lose energy significantly as they exit. Identifying high-energy particle jet suppression or "quenching" has been a primary objective since RHIC began operations in 2000.

Gabor David, a PHENIX physicist and research professor at Stony Brook University’s College of Arts and Sciences, explained how interactions within RHIC lead to energy loss: “You can think about it like the difference between running through air and running through water.” The QGP acts like water, slowing down particles so jets reach detectors with reduced energy.

In addition to energetic quarks or gluons being released during collisions, high-energy photons are also produced proportionally. By counting these photons, PHENIX scientists could measure collision centrality and determine how many jets should be expected.

Axel Drees, Distinguished Professor of Physics and Astronomy at Stony Brook University and another leader of this analysis stated: “The more central the collision is, the more interactions there can be between the quarks and gluons of a small colliding deuteron with those in a gold ion.” He noted that central collisions produce more direct photons without energy loss compared to glancing ones.

Niveditha Ramasubramanian undertook an intricate task analyzing direct photon signals from deuteron-gold collision data. Her work resolved previously unexplained increases in peripheral collision jets but showed strong suppression signals in central collisions. She commented on her unexpected findings: “The initial motivation...was only to better understand...energetic jets in peripheral collisions,” adding surprise over observed suppression during central smashups.

More details can be found on Brookhaven National Lab's website.