At Brookhaven National Laboratory on Long Island, the Relativistic Heavy Ion Collider has powered down for the last time, ending operations at the only particle collider still running in the United States. The shutdown closes a chapter in American high‑energy physics so that engineers can refit the site for a more ambitious machine, the Electron–Ion Collider. The stakes are clear: retire a proven workhorse to build a new accelerator that aims to show, in detail, how matter holds together.
The decision is not only about prestige or lab bragging rights. It is a bet that a collider built for precision, rather than raw energy, can answer questions that decades of atom smashing have left open. It is also a test of whether the United States still wants to shape the future of particle physics, or is willing to depend on access to facilities overseas while it waits for the next machine at home.
RHIC’s last run and what it achieved
The Relativistic Heavy Ion Collider, or RHIC, was a rare kind of national facility. It was the only particle collider operating in the United States, and the only one designed from the start to slam heavy ions together instead of just protons. Its twin accelerator rings, arranged like a racetrack, let two beams circulate in opposite directions before crossing and colliding. That layout made the machine flexible and well suited to study extreme states of matter, and the same two‑ring backbone is now being adapted for the next collider.
Closing RHIC is therefore more than flipping a switch. It marks the end of the only active collider program on U.S. soil, as confirmed in detailed reporting from Brookhaven. For researchers who built careers on its data, that is a real loss. Yet the machine did not fade out quietly. According to coverage of its final months, RHIC’s last run was its longest and collected more data than any earlier campaign, giving physicists a rich trove to analyze while the hardware around them is stripped down and rebuilt for what comes next.
What RHIC actually discovered
RHIC’s main mission was to recreate a hot soup of quarks and gluons, similar to the state of the universe microseconds after the Big Bang. By colliding gold ions at nearly light speed, the collider produced a fluid‑like “quark–gluon plasma” that flowed almost without resistance. Measurements showed that this plasma behaved more like a perfect liquid than a thin gas, forcing theorists to rethink how the strong nuclear force acts under extreme conditions. Those results put RHIC at the center of modern nuclear physics for more than two decades.
Over the years, RHIC experiments also revealed how protons get their spin and how matter can behave at densities far beyond those inside atomic nuclei. The collider’s detectors recorded billions of collisions, and its data helped test predictions from quantum chromodynamics, the theory of the strong interaction. Even though the beams have stopped, the final, extended run means researchers will keep publishing new results for years, turning RHIC’s swan song into a long scientific echo rather than a sudden stop.
Why the U.S. is betting on an Electron–Ion Collider
Shuttering RHIC would be much harder to defend if the tunnel were simply going dark. Instead, the same Brookhaven site is being prepared for the Electron–Ion Collider, or EIC, a new accelerator that collides electrons with ions rather than smashing two heavy nuclei together. An electron–ion collider is a different tool by design. It trades the chaos of heavy‑ion debris for cleaner, more controlled hits that can map out the internal structure of protons and nuclei in three dimensions.
The United States formally backed this plan in 2020, with an estimated cost between 1.6 billion and 2.6 billion dollars listed in federal budget summaries of the Electron–Ion Collider project. That price tag is large but in line with other flagship science efforts. It reflects a strategic choice: rather than trying to outdo Europe’s giant proton machines on energy, the U.S. is aiming for precision studies of the strong nuclear force, the interaction that glues quarks together inside protons and neutrons. In that sense, the EIC is meant to lead by asking sharper questions, not just by building a bigger hammer.
From heavy ions to electrons and ions
The shift from RHIC to the EIC is not just a new label on the same tunnel. RHIC was built to collide heavy ions, such as gold nuclei, to create tiny fireballs that briefly reached trillions of degrees. That work required two matched rings and powerful magnets to steer large, highly charged projectiles. The EIC, by contrast, will send a beam of spin‑polarized electrons into a counter‑circulating beam of ions, using the same tunnel but new injector systems, interaction regions, and detectors tuned for precision scattering.
Design documents describe the EIC as a collider built specifically to smash spin‑polarized electrons into ions, a configuration laid out in technical summaries of the evolving EIC concept. This design lets researchers flip the spin of the electron beam and see how the internal spin of the proton responds. By comparing many such collisions, they can estimate how much of a proton’s spin comes from its quarks, how much from gluons, and how much from their motion. The same setup will allow detailed tests of how quarks share momentum inside nuclei, including rare events that probe quantum effects such as entanglement between the particles.
Who is steering the transition at Brookhaven
Big machines do not retire or get built on their own. They depend on people who can argue for them in Washington and keep thousands of technical decisions aligned over many years. At Brookhaven, Interim Laboratory Director John Hill is one of the leaders managing the handoff from RHIC operations to EIC construction. On the federal side, Darío Gil, the U.S. Department of Energy’s Under Secretary for Science, has become a visible advocate for the idea that particle physics in the U.S. is not ending, but changing form.
Gil’s role as Under Secretary for Science, and Hill’s position as interim director, are both highlighted in coverage of the shutdown ceremony that brought them together at Brookhaven. Reports on that event note that Gil and Hill to mark the changeover, a symbolic pairing of federal authority and lab leadership. Their presence signaled that the Department of Energy sees the end of RHIC not as a retreat from high‑energy physics, but as the starting line for a new national facility.
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*This article was researched with the help of AI, with human editors creating the final content.
