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**ブロークヘブン国立研究所（BNL）の相対性重イオン衝突装置（RHIC）閉鎖まとめ（日本語）**
- **歴史と功績**
- 2000 年に本格稼働し、25 年間にわたり金原子核の 200 GeV/核衝突や、2002 年の新相（可能性の示唆）・2010 年の 4 兆度プラズマ（ギネス記録）・2023 年の新しい量子もつれの発見など、数多くの画期的実験を実施。
- 初期の重イオン衝突でクォーク・グルオン・プラズマ（QGP）を生成し、後に「ほぼ摩擦ゼロの完璧流体」としてその性質を解明。プロトンスピン問題の収束や、史上最大規模の反物質生成、宇宙誕生直後に近い条件の再現にも成功した。
- **最終衝突と閉鎖**
- 2026 年 2 月 6 日、DOE の科学副長官ダリオ・ジルが赤いボタンを押し、約 25 年にわたる RHIC の衝突実験が終了。研究者たちは感慨深く拍手し、長年の研究拠点であったことを惜しんだ。
- 最終走行で得られたデータは数百ペタバイトに上り、バーチャル粒子の直接観測など新たな発見も報告され、装置停止後も科学的価値は継続する。
- **後継装置：電子イオン衝突装置（EIC）**
- RHIC の地下貯蔵リングのうち 1 本を流用し、次世代の「電子‑イオン」コライダーを 10 年以内に建設予定。
- 高速電子ビームで重イオンを「ナイフ」のように切り込み、クォーク・グルオンの微細構造や最強相互作用を前例のない精度で探査できる。
- 米国初の新規コライダーとなり、過去 10‑15 年間欧州・アジアに占められていた粒子物理の舞台へ米国の再参入を象徴するプロジェクトと位置付けられる。
- **意義**
- RHIC は米国内唯一のヘッドオン衝突型加速器であり、その閉鎖は米国の加速器研究に大きな転換点をもたらす。
- EIC の稼働により、若手研究者にとって世界トップクラスの実験拠点が再び米国に確立され、次世代の基礎物理学探索が加速する見込み。
要するに、RHIC は「ビッグバンに最も近い実験装置」として25 年間にわたる数々の突破口を提供し、最終衝突で得た膨大なデータとともに閉鎖された。今後はその遺産を受け継ぎ、より強力な電子イオン衝突装置（EIC）が米国の粒子物理の新たな旗手となる。
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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