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为何宇宙中物质比反物质多?物理学家离解开谜团又近了一步

TSS EXCLUSIVE: Why Is There More Matter Than Antimatter In The Universe? Physicists Inch Closer To Solving Mystery

by Rhodilee Jean Dolor

In its infancy, the universe had equal amounts of matter and antimatter, but 14 billion years after the Big Bang, the cosmos is now predominantly made up of matter. How this exactly happened remains a mystery, but scientists could be closer to the answer with recent breakthroughs in the field of particle physics.

在宇宙诞生初期拥有着等量的物质和反物质;在大爆炸140亿年之后,宇宙现在主要由物质组成;这究竟是如何发生的仍然是一个谜,但科学家可能更接近答案,最近在粒子物理学领域的得到突破性进展。

Matter And Antimatter

物质与反物质

According to the Standard Model, which describes how the fundamental particles in the universe interact, each elementary particle has an antiparticle with the same mass but an opposite charge. These antiparticles are collectively known as antimatter.

根据描述:宇宙中基本粒子如何相互作用的标准模型,每个基本粒子都有一个质量相同但电荷相反的反粒子,而这些反粒子统称为反物质。

Because antimatter and matter have the same mass but carry opposite charges, they annihilate each other when they collide. The Standard Model posits that there were equal amounts of matter and antimatter when the universe was created, but matter eventually got the upper hand. 

因为反物质和物质具有相同的质量,却携带相反的电荷,当它们碰撞时就会湮灭;标准模型假设宇宙诞生时物质和反物质的数量相等,但物质最终占了上风。

“We have this apparent complete symmetry of accounting between matter and antimatter,” explained Thomas O’Donnell, professor of physics at Virginia Tech University. “Every time you make a piece of matter, you also make a balancing piece of antimatter, and every time you destroy a piece of matter, you must destroy a piece of antimatter. If this is true, you can never have more of one type than the other.”

弗吉尼亚理工大学的物理学教授托马斯·奥唐纳解释说:“物质和反物质之间有着明显的完全对称关系;每制造一件物质,同时又制造了一件平衡的反物质,每摧毁一件物质,那也必须摧毁一件反物质;若是真的,那你不可能拥有更多的一种类型比另一种。”

How matter dominated the universe is still unclear, but two new studies may hold the potential answer to this long-standing mystery.

物质是如何支配宇宙的仍旧尚不清楚,但两项新研究可能为这个长期以来的谜题提供了可能的答案。

Nuclei In Thorium-228 Atoms

钍228原子的原子核

Dr. David O’Donnell, lecturer in the Nuclear Physics Group at the University of the West of Scotland, and colleagues discussed the properties of an element that may help explain why matter now exists more abundantly than antimatter.

苏格兰西部大学核物理小组的讲师David O ‘Donnell博士和他的同事们共同讨论了一种元素的特性,这种特性可能有助于解释为什么现在物质比反物质多。

Scientists think that the so-called electric dipole moment (EDM) allows matter and antimatter to decay at different rates, which can help explain the asymmetry of matter and antimatter beyond the Standard Model. 

科学家们认为:所谓的电偶极矩(EDM)允许物质和反物质以不同的速度衰变,这有助于解释物质和反物质的不对称性也超出了标准模型。

Physicists also believe that they can best observe EDM in pear-shaped nuclei because the protons and neutrons are not evenly distributed in the nuclear volume. 

物理学家还认为,他们能最好地观察到梨形核(pear-shaped nucleus)中的电火花加工,因为质子和中子在核体积中不是均匀分布的。

In their study published in the journal Nature Physics on May 18, O’Donnell and colleagues revealed that thorium-228 atoms so far have the most pronounced pear-shaped nucleus that has been discovered to date. 

在5月18日发表在《自然物理》杂志上的研究中,O ‘Donnell和他的同事揭示了迄今为止发现的最明显的梨形核是由钍228原子组成的。

“These nuclei present a promising avenue in the search for a permanent atomic electric dipole moment—the existence of which has implications for physics beyond the Standard Model of particle physics,” the researchers wrote in their study. “This study indicates that the nuclei 229Th and 229Pa (Z = 91) may be good candidates for the search for a permanent atomic electric dipole moment.”

研究人员在他们的研究报告中写道:“这些原子核为寻找永久的原子电偶极矩提供了一条有希望的途径——原子电偶极矩的存在对物理学的意义超出了粒子物理学的标准模型。”“这项研究表明,原子核229和229Pa (Z = 91)可能是寻找永久原子电偶极矩的良好候选者。”

Neutrino Oscillations
中微子振荡

Another study, published in the journal Nature on April 15 also holds promise in solving the matter-antimatter asymmetry.

另一项发表在4月15日《自然》(Nature)杂志上的研究也有望解决”物质—反物质”(matter-antimatter)的不对称性。

The research involves neutrinos, one of the fundamental particles of the universe. Neutrinos come in three flavours, namely electron, muon and tau, that may spontaneously change, or oscillate, from one to another as they travel, a phenomenon known as neutrino oscillation. 

这项研究涉及到中微子——宇宙的基本粒子之一。中微子有三种形式: 电子、介子和玻色子,它们在传播过程中可能会自发地从一个粒子到另一个粒子发生变化或振荡,这种现象被称为中微子振荡。

Using data from the Tokai to Kamioka (T2K) project in Japan, which conducts experiments to investigate how neutrinos change from one flavor to another as they travel, researchers found evidence that backs up the role of neutrinos in the current abundance of matter.  

利用日本Tokai to Kamioka (T2K)项目的数据,研究人员发现了支持中微子在当前大量物质中所起作用的证据;T2K项目进行实验,研究中微子在传播过程中如何从一种形式转变成另一种形式。

Each of the three neutrino flavors have a corresponding antineutrino. If the flavors change or oscillate differently for neutrinos and antineutrinos, it could explain the dominance of matter in the universe. 

这三种中微子中都有相应的反中微子。如果中微子和反中微子发生变化或振荡不同,这就可以解释宇宙中物质的主导地位。

Researchers have been looking for a source of the so-called Charge-Parity (CP) symmetry in neutrino oscillations which may show up as a difference in the measured oscillation probability for neutrinos and antineutrinos.

研究人员一直在寻找中微子振荡中所谓的Charge-Parity (CP,又叫CP对称)对称性的来源,这种对称性可能表现为测量到的中微子和反中微子振荡概率的差异。

T2K experiments use beams of muon neutrinos or muon antineutrinos that travel from the Japan Proton Accelerator Research Complex (J-PARC) in Tokai village to the Super-Kamiokande detector, which lies under a mountain in Kamioka, nearly 300 kilometers away. 

T2K实验使用的是介子中微子或反中微子束,它们从位于Tokai村的日本质子加速器研究中心(J-PARC)传输到超级神冈探测器,该探测器位于近300公里之外的神冈市的一座山下。

In these experiments, a few of the beam particles from Tokai are flagged by a detector at the Kamioka Observatory that contains ultrapure water. Once a neutrino interacts with a neutron in the tank, it produces a muon or an electron, which is further analyzed to reveal the oscillation of different neutrino flavors. 

在这些实验中,来自东海的一些粒子束被Kamioka天文台的一个含有超纯水的探测器标记出来;一旦中微子在容器中与中子相互作用,它就会产生一个介子或一个电子,这些介子或电子会被进一步分析,以揭示不同形式中微子的振荡。

Using data from the experiments, Atsuko Ichikawa, from Kyoto University in Japan, and colleagues reported that they found evidence showing that neutrinos and antineutrinos oscillate in different ways.

利用来自实验的数据,日本京都大学的市川广子和他的同事报告说,他们发现了中微子和反中微子以不同方式振荡的证据。

“It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis,” Ichikawa and colleagues wrote in their study. “This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments.”

Ichikawa和他的同事在他们的研究中写道:“已经证明轻子的CP破坏可以通过一个被称为轻子形成的过程来产生物质-反物质的差异,这种CP违逆可以用介子中微子到电子中微子的振荡以及相应的反中微子振荡来测量,这些振荡可以用加速器产生的光束来测量,这是由tokaito kamioka (T2K)和NOvA实验建立的。”

The physicists said that the results do not yet provide the best demonstration of CP violation with neutrinos and antineutrinos. Nonetheless, they believe that development represents an important step towards the observation of CP violation. 

物理学家们说,这些结果还不能最好地证明中微子和反中微子对CP的破坏;尽管如此,他们认为发展是观察CP对称性的重要一步。

Key To Unlocking Mysteries Of Life And The Universe

解开生命和宇宙奥秘之匙

Scientists are interested in the phenomenon that created the current imbalance between matter and antimatter because this can help shed light on how life came into existence. The universe as we know it may not have existed had the particles of matter and antimatter collided with perfect efficiency according to the laws of physics.

科学家们对造成目前物质和反物质不平衡的现象很感兴趣,因为这有助于解释生命是如何形成的;而我们所知的宇宙可能并不不存在,但根据物理定律来看,物质和反物质的粒子以完美的效率碰撞。

Physicists Silvia Pascoli, from the University of Durham in England, and Jessica Turner, from the U.S. Department of Energy’s Fermilab in Illinois, cited the implications of the T2K study.

英国杜伦大学的物理学家西尔维娅·帕斯克(Silvia Pascoli)里和美国能源部伊利诺斯州费米实验室的杰西卡·特纳(Jessica Turner)引用了T2K研究的结论。

“These results could be the first indications of the origin of the matter–antimatter asymmetry in our universe,” Pascoli and Turner wrote.

“这些结果可能是宇宙中物质-反物质不对称起源的第一个迹象,”Pascoli和Turner写道。

“This imbalance, at a level of a few particles per 10 billion photons is ultimately responsible for the existence of Earth, planets, stars and ourselves: if there were equal amounts of matter and antimatter, they would have destroyed each other in the early Universe and annihilated into photons. No matter would have remained.”

“这种不平衡在每100亿个光子中只有几个粒子的概率中,最终导致了地球、行星、恒星和我们自己的存在:若有等量的物质和反物质,它们会在早期的宇宙中相互毁灭,然后湮灭成光子;无论如何这都会留下。”

翻译:SCGS翻译组

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