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**ブロークヘイブン国立研究所（BNL）・相対論的重イオン衝突装置（RHIC）閉鎖の概要（2026年2月6日）**
- **最終衝突と閉鎖式**
- 2月6日、BNLの制御室に科学者・管理者・報道陣が集まり、米エネルギー省科学担当副長官ダリオ・ジルが赤いボタンを押して、25年にわたるRHICの運転を終了。長年同装置で研究してきた加速物理学者エンジェリカ・ドリーズらは「寂しい」「美しい実験だった」と感慨を述べた。
- **RHICの主な功績（2000‑2025） -**
- 2001年に金原子核の200 GeV/nucleon衝突を初実現。
- 2002年には新しい物質相の可能性を示唆。
- 2010年には約4兆度のプラズマを作り、ギネス世界記録を樹立。
- 2023年に全く新しい量子もつれを発見。
- 重イオン衝突でクォーク・グルーオンプラズマ（QGP）を生成し、液体様の「ほぼ完璧」な流体（摩擦ゼロ、非常に高い渦度）であることを実証。
- プロトンのスピン問題の解決に寄与し、反物質の最大規模生成やビッグバン初期状態の再現に成功。
- 2025年の最終走行では、QGP中での「仮想粒子」の直接観測という新発見をもたらし、数百ペタバイト規模のデータが蓄積された。
- **次世代装置：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、電子ビーム用リングに置き換えて建設予定（次の10年で完成）。
- 電子を「ナイフ」のように使い、金イオン内部を高精度に探査し、クォーク・グルーオンの構造や最強相互作用をさらに詳しく調べることが目的。
- 米国で初の新規粒子加速器となり、欧州・アジアに後れを取っていた米国の粒子物理学を再び世界の最前線に押し上げると期待されている。
- 「少なくとも10〜15年は、若手研究者にとって世界一の拠点になる」― BNL副所長アブハイ・デシュパンドのコメント。
- **意義**
- RHICは米国唯一の対向ビーム粒子衝突装置であり、世界でも唯一のタイプだった。閉鎖はその時代の終焉を示すが、蓄積された膨大なデータと得られた知見は今後も科学研究に活用される。
- EICへの移行は「甘くないが必要な別れ」― RHICの遺産を引き継ぎつつ、より強力な実験基盤へと進化させる重要なステップである。
**要点**：25年にわたるRHICの運転は、QGPの実証、反物質生成、スピン問題の解決など多くの画期的成果をもたらした。最終衝突後、同施設の一部を利用した次世代電子・イオン衝突装置（EIC）が建設され、米国の粒子物理学は新たな時代へと踏み出す。
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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