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**ブロークヘイブン国立研究所（BNL）で25年にわたって稼働した相対論的重イオン衝突型加速器（RHIC）が2026年2月6日、最後の衝突を終えて閉鎖されました。**
- **歴史と成果**
- 2000年に本格運転開始。金イオン同士の衝突で初めて200 GeV/核のエネルギーを実現（2001年）。
- 2002年に新種の物質候補、2010年には4兆度（約4 × 10¹² K）という史上最高温度のプラズマを生成しギネス記録に認定。
- プロトンスピン問題の解消、最も重く複雑な反物質の生成、ビッグバン直前のクォーク・グルオン・プラズマ（QGP）を液体様に観測するなど、素粒子・核物理の最前線を牽引。
- 最終走行では「仮想粒子」の直接観測という新たな量子真空の探査結果が得られ、数百ペタバイト規模のデータが蓄積された。
- **閉鎖の経緯**
- 米エネルギー省（DOE）科学担当副長官ダリオ・ジル氏が赤いボタンを押し、感慨深い拍手とともにRHICの運転が終了。
- 「寂しいが、もっと優れた装置を建てる」という期待が示された。
- **次世代装置：電子・イオン衝突型加速器（EIC）**
- RHICの地下リングの一部を流用し、約10年かけて新たに建設予定。
- 電子ビームを用いてイオンを「ナイフ」のように切り込み、クォークとグルオンの構造をより高精度で探査できる。
- 米国で初の新規粒子加速器となり、欧州・アジアに遅れを取っていた米国粒子物理学の再興を象徴。
**結論**
RHICは「唯一の米国内ヘビーレイオン対向衝突装置」として、素粒子物理学に革命的知見をもたらした。その科学遺産は膨大なデータとして残り、次世代EICへと受け継がれることで、今後も米国が世界の最前線で研究を続ける基盤となる。
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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