sPHENIX Detector Poised to Uncover Secrets of the Early Universe

In a groundbreaking development for particle physics, the sPHENIX detector has successfully completed a pivotal test, positioning it to explore the remnants of the primordial soup that filled the universe just after the Big Bang. This state-of-the-art detector operates within the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in Upton, New York, the second most powerful particle accelerator globally, trailing only the Large Hadron Collider (LHC).

The RHIC accelerates protons and heavy ions, such as gold, to nearly the speed of light, facilitating collisions that recreate conditions akin to those just moments after the universe’s inception. These collisions produce a rare state of matter known as quark-gluon plasma, a “soup” of free quarks and gluons—the fundamental constituents of protons. By studying this plasma, scientists hope to glean insights into the universe’s earliest moments and the processes that led to the formation of protons and neutrons, ultimately shaping the matter we observe today.

The recent test, referred to as a “standard candle” in particle physics, is crucial for validating the detector’s capabilities. Unlike the astronomical standard candles used to measure cosmic distances, this standard candle relates to a well-established constant used to assess a detector’s precision. The sPHENIX team successfully measured the particle production resulting from gold ion collisions at relativistic speeds, demonstrating that head-on collisions produced ten times more particles than glancing ones, with a corresponding increase in energy.

“This indicates the detector works as it should,” noted Gunther Roland, a member of the sPHENIX Collaboration and a physics professor at the Massachusetts Institute of Technology (MIT). He likened the achievement to the moment a newly launched telescope captures its first image, affirming the detector’s readiness for groundbreaking scientific exploration.

Quark-gluon plasma is ephemeral, existing only for a sextillionth of a second. During this brief period, it reaches temperatures of trillions of degrees, behaving as a “perfect fluid” rather than a disordered collection of particles. As the plasma cools, it transforms into protons and neutrons, which then disperse from the collision site. “You never see the quark-gluon plasma itself—you just see its ashes, so to speak, in the form of the particles that come from its decay,” Roland explained.

The sPHENIX detector, comparable in size to a two-story house and weighing around 1,000 tons, is designed to capture and analyze up to 15,000 particle collisions per second. As the successor to the Pioneering High Energy Nuclear Interaction Experiment (PHENIX), it incorporates advanced detector technologies developed over the past 25 years, enabling unprecedented data collection rates.

The sPHENIX team conducted the standard candle test over three weeks in the fall of 2024, marking a significant milestone in their research journey. “The fun for sPHENIX is just beginning,” remarked Cameron Dean, an MIT researcher and team member. “We are currently back colliding particles and expect to do so for several more months. With all our data, we can look for the one-in-a-billion rare process that could give us insights on things like the density of QGP, the diffusion of particles through ultra-dense matter, and how much energy it takes to bind different particles together.”

The findings from this research were published in the August edition of the Journal of High Energy Physics, promising exciting advancements in our understanding of the universe’s fundamental structure and the forces that govern it. As the sPHENIX detector embarks on its scientific mission, the anticipation builds for the revelations it may unveil about the very fabric of our cosmos.