The Omega Baryon

The Omega-Minus Baryon

Omega-负重子

Particle 质点	Symbol 符号	Makeup 组成	Rest mass MeV/c² 静止质量 MeV/c²	Spin 自旋	B	S	Lifetime 寿命	Decay Modes 衰变模式
Omega 欧米伽	Ω^-	sss sss（专名或术语）	1672	3/2	+1	-3	0.82 x10^-10	Ξ⁰π^-, Λ⁰K^-

The omega-minus, a baryon composed of three strange quarks, is a classic example of the need for the property called "color" in describing particles. Since quarks are fermions with spin 1/2, they must obey the Pauli exclusion principle and cannot exist in identical states. So with three strange quarks, the property which distinguishes them must be capable of at least three distinct values.

omega减粒子，由三个奇异夸克组成，是需要在描述粒子时引入称为‘色’的性质的经典例子。由于夸克是自旋为1/2的费米子，它们必须遵守泡利不相容原理，不能处于相同的状态。因此，三个奇异夸克之间的区别属性必须至少有三个不同的值。

The discovery of the omega baryon was a great triumph for the quark model of baryons because it was searched for and found only after its existence, mass, and decay modes were predicted by the quark model. It was discovered at Brookhaven in 1964. At left is a sketch of the bubble chamber photograph in which the omega-minus baryon was discovered.

重子omega的发现是对重子夸克模型的重大胜利，因为该重子的存在、质量及衰变模式是在其被夸克模型预测之后才被发现的。它于1964年在布鲁克海文实验室被发现。左图是泡室照片，其中展示了omega负重子的发现。

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

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

The omega-minus was produced by a K^-p collision which produced the omega-minus and two kaons.

omega负粒子是由K粒子与质子的碰撞产生的，该碰撞产生了omega负粒子和两个K介子。

Considering the particle conservation laws, this interaction conserves strangeness and therefore proceeds by the strong interaction. The decays observed are as follows.

考虑质点守恒定律，这种相互作用 conserve 强相互作用。观察到的衰变如下。

Note that all three of these decays violate strangeness conservation and therefore can proceed only by the weak interaction. This gives them longer lifetimes, on the order of
10^-10 seconds.

注意，这三个衰变过程都违反了 strangeness conservation，因此只能通过弱相互作用进行。这使得它们的寿命更长，大约为 10 -10 秒。

Examining the decays of the omega-minus above, you see that a quark-antiquark pair can be added on the right, provided the process satisfies conservation of energy. It is expected that the strange quark will be transmuted to an up quark by a quark decay process involving the W^- vector boson. This can produce an electron plus and antineutrino, but an alternative W^- process involves the production of an up plus an antiup-down (a π^- meson). It appears that alternative decay is operating here.

在考察omega负子的衰变时，你看到可以在右边添加一个夸克-反夸克对，只要该过程满足能量守恒。预计通过涉及W-矢量玻色子的夸克衰变过程，奇夸克会转化为上夸克。这可以产生一个电子和反中微子，但另一种W-过程涉及产生一个上夸克和一个反上夸克（一个π-介子）。似乎这里正在发生另一种衰变过程。

In the decay of the Xi particle above, 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. It is just that the π⁰ decays into two gammas with a lifetime of about 10^-16 seconds, so the two gamma rays appear to come from the same point as the lambda.

在上述Xi粒子的衰变中，显示的是一个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。只是因为Pi-零衰变成两个伽马射线，其寿命约为10⁻¹⁶秒，所以两个伽马射线看起来像是从同一个点发出的，如同Lambda粒子一样。

According to the Particle Data Book, the decays of the omega minus branch are as follows:
Λ⁰K^- 67.8%, Ξ⁰π^- 23.6%, and Ξ^-π⁰ 8.6%.

根据粒子数据书，omega负子的衰变分支如下：Λ⁰ → K⁻占67.8%，Ξ⁰ → π⁻占23.6%，和Ξ⁻ → π⁰占8.6%。