Antiparticles

In the standard model for describing fundamental particles and interactions, every particle has an antiparticle. For example, the positron is the antiparticle of the electron. It has identical mass, but has a positive charge. If an electron encounters a positron, they annihilate with the transformation of their mass energies into two gamma rays.

在描述基本粒子和相互作用的标准模型中，每个粒子都有一个反粒子。例如，正电子是电子的反粒子。它具有相同的质量，但带有正电荷。如果电子遇到正电子，它们会湮灭，将它们的质量能量转化为两个伽马射线。

Going beyond the basics, we can say that an antiparticle is related to the particle by charge conjugation. This includes more than just electric charge; it inverts all internal quantum numbers such as baryon number, lepton number, and strangeness.

超越基础内容，我们可以指出，反粒子与粒子之间通过电荷共轭相关联。这不仅涉及电荷，还涉及所有内部量子数，如重子数、轻子数和 strangeness 的翻转。

Seeing that nature is in so many respects symmetric, a fundamental question is "Why is the universe made out of matter, with very little antimatter? We can create antimatter today in pair production, and in fact the processes of particle production produce equal numbers of particles and antiparticles. Something very early in the history of the universe tipped the balance toward matter to the virtual exclusion of antimatter. We see antimatter today only in pair production, radioactive decay and in the products of the high-energy particle accelerators.

鉴于自然界在许多方面都具有对称性，一个基本问题是‘为什么宇宙由物质构成，而反物质却非常少？我们今天可以通过对称产生反物质，事实上，粒子产生过程产生的粒子和反粒子数量相等。宇宙历史的某个早期阶段使物质的优势远超反物质，几乎排除了反物质的存在。我们今天只能在对称产生、放射性衰变以及高能粒子加速器的产物中观察到反物质。

The question is an open one. Current research which may shed some light on the question is that which explores the apparent violation of CP invariance in the decay of the neutral kaon. At the fundamental particle level, nature can tell the difference between left-handed and right-handed systems as indicated by parity violation with neutrinos (neutrinos are left-handed and antineutrinos are right-handed). While normal beta decay violates parity, it is invariant under CP. If the neutral kaon is confirmed to directly violate CP, it may provide an avenue for nature to show a preference for matter over antimatter in the early universe.

这个问题尚无定论。目前可能对这个问题有所启发的研究是探讨中性K介子衰变中出现的CP不变性违反现象。在基本粒子层面，自然界能够区分左右手系统，这由中微子的宇称违反现象所表明（中微子是左-handed，反中微子是右-handed）。虽然正常β衰变违反宇称，但其在CP变换下是不变的。如果中性K介子被证实直接违反CP，这可能为自然界在早期宇宙中表现出对物质优于反物质的偏好提供一条途径。