The Xi Baryon

Ξ重子

Particle 质点	Symbol 符号	Makeup 组成	Rest mass MeV/c² 静止质量 MeV/c²	B	S	Lifetime 寿命	Decay Modes 衰变模式
Xi Cascade Xi Cascade（专名或术语）	Ξ⁰	uss uss（专名或术语）	1315	1/2	+1	-2	2.9 x10^-10	Λ⁰π⁰
Xi Cascade Xi Cascade（专名或术语）	Ξ^-	dss dss（专名或术语）	1321	1/2	+1	-2	1.64 x10^-10	Λ⁰π^-

V. E. Barnes et al., Phys. Rev. Lett. 12, 204 (1964)

V. E. Barnes 等人，Phys. Rev. Lett. 12, 204 (1964)

The Xi or "cascade" baryon was seen in the same reaction which led to the discovery of the omega-minus baryon at Brookhaven in 1964. At left is a sketch of the bubble chamber photograph in which the omega-minus baryon was discovered. The decay of the Xi indicated in the diagram is

Xi 或‘级联’重子是在1964年在布鲁克海文发现omega负重子的同一反应中被观测到的。图中是泡室照片，其中发现了omega负重子。图中所示的Xi衰变过程是

In this decay of the Xi particle, a lambda baryon and two gamma rays are shown as the products. Actually, the primary decay of the Xi is to a lambda-zero and a pi-zero meson. This cannot be a purely electromagnetic decay because strangeness is not conserved. Also, it's lifetime in the range of 10^-10 seconds puts it in the common range for weak-interaction decays. It is just that the π⁰ decays into two gammas with a lifetime of about 10^-16 seconds (an electromagnetic decay), so the two gamma rays appear to come from the same point as the lambda.

在Xi粒子的衰变中，显示了一个Lambda重子和两个伽马射线作为产物。实际上，Xi粒子的主要衰变产物是Lambda-零和Pi-零介子。这不能是纯粹的电磁衰变，因为 strangeness 不被守恒。此外，其寿命在10^-10秒范围内，处于弱相互作用衰变的常见范围。只是Pi-零衰变成两个伽马射线的寿命约为10^-16秒（一个电磁衰变），所以两个伽马射线似乎来自同一点，如同Lambda粒子一样。

We can hypothesize pathways for the decays of the Xi baryon by making use of Feynman diagrams and the quark transformation modes associated with the weak interaction.

我们可以利用费曼图和与弱相互作用相关的夸克变换模式，来假设Ξ重子衰变的路径。

Note that these are just suggestions of pathways. The Xi-minus decay certainly seems plausible and follows the pattern shown in other decays. The Xi-zero decay is going a bit further out on a limb since it invokes two W-bosons. It is a slower process, but one would think that a double-W process would inhibit the decay by a larger factor.

请注意，这些只是可能的路径示例。Xi负粒子的衰变显然很合理，并遵循其他衰变所展示的模式。Xi零粒子的衰变则更远离主流，因为它涉及两个W玻色子。这是一个较慢的过程，但人们可能会认为双W过程会通过更大的因素抑制衰变。