##科学家首次观测到最重反物质超核，揭示宇宙之谜迈出重要一步
**中新网北京8月21日电 (记者 孙自法)** 是什么原因导致宇宙中正反物质数量的巨大差异？为了解答这个困扰科学界多年的谜题，科学家们一直在实验室中制造新的反物质并研究它们的性质。近日，中国科学院近代物理研究所仇浩研究员团队等在参与RHIC-STAR国际合作实验研究中取得重大突破，首次在相对论重离子金金碰撞中观测到一种新的反物质超核——反超氢-4，这也是迄今实验上发现的最重的反物质超核。这一重要发现已于北京时间8月21日夜间发表在国际著名学术期刊《自然》上。
当前的物理学知识认为物质和反物质的性质是对称的，宇宙诞生之初应该存在等量的正物质和反物质。然而，某种神秘的物理机制导致早期宇宙中正反物质数量极小的不对称，在绝大部分正反物质湮灭后，仅有约百亿分之一的正物质得以存活下来，构成了今天的物质世界。
反物质非常罕见，而由若干反重子进一步组合形成的反物质原子核和反物质超核（即包含Lambda等超子的原子核），则更加难以产生。自1928年狄拉克方程的“负能量解”预示反物质的存在以来近一个世纪，科学家仅发现6种反物质（超）核。
此次发现的反超氢-4是在位于美国布鲁克海文国家实验室的相对论重离子对撞机（RHIC）中产生的。RHIC能够将重离子束加速至接近光速并使其对撞，模拟宇宙早期大爆炸的状态，产生几万亿摄氏度的高温火球，包含几乎等量的正物质与反物质。研究团队分析了共约66亿个重离子碰撞事件的实验数据，通过衰变产生的反氦-4和π+介子反向重建反超氢-4，最终获得约16个反超氢-4的信号。
研究团队还测量了反超氢-4的寿命，并与其对应的正粒子超氢-4比较，在测量精度范围内两者寿命没有明显差异，再次验证了正反物质性质的对称性。
科学家们表示，反超氢-4是目前观测到的最重的反物质超核，其发现和性质研究，使人们在反物质及正反物质对称性的探索方面又迈出重要一步。未来，科学家们将继续利用RHIC-STAR实验，探索更重的反物质超核，深入研究反物质的性质，为揭示宇宙中正反物质不对称之谜提供更多线索。
据了解，RHIC-STAR大型国际实验合作组由来自14个国家、74个单位的700多位研究人员组成。这次反超氢-4观测发现及研究工作由仇浩团队主导完成，中国科学院近代物理研究所博士生吴俊霖、路坦在物理分析中做出突出贡献；中国科学技术大学团队在衰变粒子重建技术方面提供重要支持。
英语如下：
##Antimatter Research Makes Major Breakthrough: Scientists Observe Heaviest Antimatter Hypernucleus!
**Keywords:** Antimatter, Hypernucleus, Universe
## ScientistsObserve Heaviest Antimatter Hypernucleus for the First Time, Taking a Major Step Towards Unveiling Cosmic Mysteries
**BEIJING, Aug. 21 (Xinhua)** — What caused the vast disparity in the amount of matter and antimatter in the universe? To answer this question that has plagued the scientific communityfor years, scientists have been creating new antimatter in laboratories and studying its properties. Recently, a team led by researcher Qiu Hao from the Institute of Modern Physics, Chinese Academy of Sciences, achieved a major breakthrough in the RHIC-STARinternational collaboration experiment, observing a new antimatter hypernucleus – anti-hypertriton-4 – for the first time in relativistic heavy-ion gold-gold collisions. This is also the heaviest antimatter hypernucleus discovered experimentally to date.This significant discovery was published in the renowned international academic journal *Nature* on the night of August 21st, Beijing time.
Current physics knowledge suggests that matter and antimatter have symmetrical properties, and the early universe should have contained equal amounts of both. However, some mysterious physical mechanism led to a tiny asymmetryin the amount of matter and antimatter in the early universe. After the annihilation of most matter and antimatter, only about one in ten billion parts of matter survived, forming the material world we see today.
Antimatter is extremely rare, and antimatter nuclei and antimatter hypernuclei (nuclei containing hyperons like Lambda), formed by further combinations of several antibaryons, are even more difficult to produce. Since the prediction of antimatter by Dirac’s equation in 1928, scientists have only discovered six antimatter (hyper)nuclei.
The newly discovered anti-hypertriton-4 wasproduced at the Relativistic Heavy Ion Collider (RHIC) located at the Brookhaven National Laboratory in the United States. RHIC can accelerate heavy ion beams to near the speed of light and collide them, simulating the conditions of the early universe’s Big Bang, creating a fireball with temperatures of trillions of degreesCelsius, containing almost equal amounts of matter and antimatter. The research team analyzed experimental data from about 6.6 billion heavy ion collision events, reconstructing anti-hypertriton-4 from the decay products anti-helium-4 and π+ mesons in reverse, ultimately obtaining a signal of about16 anti-hypertriton-4.
The research team also measured the lifetime of anti-hypertriton-4 and compared it to its corresponding positive particle, hypertriton-4. Within the measurement accuracy, there was no significant difference in their lifetimes, further verifying the symmetry of matter and antimatterproperties.
Scientists say that anti-hypertriton-4 is the heaviest antimatter hypernucleus observed so far, and its discovery and property research represent a significant step forward in the exploration of antimatter and the symmetry of matter and antimatter. In the future, scientists will continue to utilize the RHIC-STARexperiment to explore heavier antimatter hypernuclei, delve deeper into the properties of antimatter, and provide more clues to unravel the mystery of matter-antimatter asymmetry in the universe.
It is understood that the RHIC-STAR large international experimental collaboration group consists of over 700 researchers from 74institutions in 14 countries. The observation and research of anti-hypertriton-4 were led by Qiu Hao’s team, with outstanding contributions from PhD students Wu Junlin and Lu Tan from the Institute of Modern Physics, Chinese Academy of Sciences, in the physical analysis. The team from the University of Scienceand Technology of China provided important support in the reconstruction technology of decay particles.
【来源】http://www.chinanews.com/gn/2024/08-21/10272668.shtml
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