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**ブロークヘイブン国立研究所（BNL）の相対論的重イオン衝突型加速器（RHIC）閉鎖概要（2026年2月）**
- **最終衝突**：2026年2月6日、制御室で米エネルギー省のダリオ・ジル副長官が赤いボタンを押し、25年にわたるRHICの運転を終了。参加者は惜しみつつ拍手で見送った。
- **後継装置**：同敷地に新たに**電子イオン衝突型加速器（EIC）**を建設予定。RHICの地下リングの一つを流用し、電子ビームで重イオン（金イオン）を「ナイフ」のように切り込むことで、クォークとグルオンの構造を精密に探査する。建設は今後10年で完了見込みで、米国初の新規粒子加速器となる。
- **科学的功績**
- 2000年の本格稼働以降、金原子核同士の衝突で**クォーク・グルオン・プラズマ（QGP）**を生成し、2010年に「ほぼ完璧な液体」―摩擦ゼロ、非常に高い渦度を持つ状態であることを実証。
- プロトンのスピン問題の解明に寄与し、最初にスピンが整列した2つの陽子ビームを衝突させた実績を持つ唯一の実験でもある。
- 2025年の最終走行で**仮想粒子**の直接観測という新たな証拠を取得し、量子真空の探査に新境地を開いた。
- 走行中に生成されたデータは数百ペタバイトに達し、衝突が止まっても解析は続く。
- **意義**：RHICの閉鎖は米国内唯一の対向ビーム型加速器の終了を意味するが、EICの建設により米国は粒子物理の最前線へ再参入し、次世代の若手研究者にとって世界屈指の拠点となる見通し。
RHICは「最も熱い人工プラズマ」「最大規模の反物質生成」「宇宙初期状態への接近」など、25年にわたり基礎物理学に革命的貢献を果たした。閉鎖は別れであると同時に、EICへと受け継がれる新たな探求の始まりでもある。
2001: "Brookhaven Labs has produced for the first time collisions of gold nuclei at a center of mass energy of 200GeV/nucleon."
2002: "There may be a new type of matter according to researchers at Brookhaven National Laboratory."
2010: The hottest man-made temperatures ever achived were a record 4 trillion degree plasma experiment at Brookhaven National Laboratory in New York... anointed the Guinness record holder."
2023: "Scientists at Brookhaven National Laboratory have uncovered an entirely new kind of quantum entanglement."
2026: On Friday, February 6, "a control room full of scientists, administrators and members of the press gathered" at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab in Upton, New York to witness its final collisions, reports Scientific American:
The vibe had been wistful, but the crowd broke into applause as Darío Gil, the Under Secretary for Science at the U.S. Department of Energy, pressed a red button to end the collider's quarter-century saga... "I'm really sad" [said Angelika Drees, a BNL accelerator physicist]. "It was such a beautiful experiment and my research home for 27 years. But we're going to put something even better there."
That "something" will be a far more powerful electron-ion collider to further push the frontiers of physics, extend RHIC's legacy and maintain the lab's position as a center of discovery. This successor will be built in part from RHIC's bones, especially from one of its two giant, subterranean storage rings that once held the retiring collider's supply of circulating, near-light speed nuclei...slated for construction over the next decade. [That Electron-Ion Collider, or EIC] will utilize much of RHIC's infrastructure, replacing one of its ion rings with a new ring for cycling electrons. The EIC will use those tiny, fast-flying electrons as tiny knives for slicing open the much larger gold ions. Physicists will get an unrivaled look into the workings of quarks and gluons and yet another chance to grapple with nature's strongest force. "We knew for the EIC to happen, RHIC needed to end," says Wolfram Fischer, who chairs BNL's collider-accelerator department. "It's bittersweet."
EIC will be the first new collider built in the US since RHIC. To some, it signifies the country's reentry into a particle physics landscape it has largely ceded to Europe and Asia over the past two decades. "For at least 10 or 15 years," says Abhay Deshpande, BNL's associate laboratory director for nuclear and particle physics, "this will be the number one place in the world for [young physicists] to come."
The RHIC was able "to separately send two protons colliding with precisely aligned spins — something that, even today, no other experiment has yet matched," the article points out:
During its record-breaking 25-year run, RHIC illuminated nature's thorniest force and its most fundamental constituents. It created the heaviest, most elaborate assemblages of antimatter ever seen. It nearly put to rest a decades-long crisis over the proton's spin. And, of course, it brought physicists closer to the big bang than ever before...
When RHIC at last began full operations in 2000, its initial heavy-ion collisions almost immediately pumped out quark-gluon plasma. But demonstrating this beyond a shadow of a doubt proved in some respects more challenging than actually creating the elusive plasma itself, with the case for success strengthening as RHIC's numbers of collisions soared. By 2010 RHIC's scientists were confident enough to declare that the hot soup they'd been studying for a decade was hot and soupy enough to convincingly constitute a quark-gluon plasma. And it was even weirder than they thought. Instead of the gas of quarks and gluons theorists expected, the plasma acted like a swirling liquid unprecedented in nature. It was nearly "perfect," with zero friction, and set a new record for twistiness, or "vorticity." For Paul Mantica, a division director for the Facilities and Project Management Division in the DOE's Office of Nuclear Physics, this was the highlight of RHIC's storied existence. "It was paradigm-changing," he says...
Data from the final run (which began nearly a year ago) has already produced yet another discovery: the first-ever direct evidence of "virtual particles" in RHIC's subatomic puffs of quark-gluon plasma, constituting an unprecedented probe of the quantum vacuum.
RHIC's last run generated hundreds of petabytes of data, the article points out, meaning its final smash "isn't really the end; even when its collisions stop, its science will live on."
But Science News notes RHIC's closure "marks the end for the only particle collider operating in the United States, and the only collider of its kind in the world. Most particle accelerators are unable to steer two particle beams to crash head-on into one another."
Read more of this story at Slashdot.
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