Bag Model of Quark Confinement

夸克禁闭的袋模型

In dealing with the nature of quark confinement, one visualization is that of an elastic bag which allows the quarks to move freely around, as long as you don't try to pull them further apart. But if you try to pull a quark out, the bag stretches and resists.

在讨论夸克禁闭的本质时，有一种可视化方式是将它想象成一个弹性袋，允许夸克在其中自由运动，只要你不试图将它们拉得更远。但如果试图将一个夸克拉出，袋就会伸展并产生阻力。


The quarks of a proton are free to move within the proton volume 质子中的夸克可以在质子体积内自由运动	If you try to pull one of the quarks out, the energy required is on the order of 1 GeV per fermi, like stretching an elastic bag. 如果你试图拉出一个夸克，所需能量约为每费米1 GeV，就像拉伸一个弹性袋一样。	The energy required to produce a separation far exceeds the pair production energy of a quark-antiquark pair, so instead of pulling out an isolated quark, you produce mesons as the produced quark-antiquark pairs combine. 产生分离所需的能量远超过夸克-反夸克对的产生能量，因此不是将孤立的夸克拉出，而是让产生的夸克-反夸克对结合形成介子。

The models of quark confinement help in understanding why we have not seen isolated quarks. If one of the constituent quarks of a particle is given enough energy, it can create a jet of mesons as the energy imparted to the quark is used to produce quark-antiquark pairs.

Experiments show that the forces containing the quarks get weaker as the quarks get closer together, so that within the confines of a baryon or hadron, they are essentially free to move about. This condition is referred to as "asymptotic freedom".

实验表明，当夸克彼此靠近时，包含夸克的力会变弱，因此在重子或强子的内部，它们基本上可以自由移动。这种条件被称为‘渐近自由’。

Index

Particle concepts

Reference
Rohlf
Ch. 18

索引质点概念参考 Rohlf 第18章

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Asymptotic Freedom

渐近自由

As the quarks within a meson or baryon get closer together, the force of containment gets weaker so that it asymptotically approaches zero for close confinement. The implication is that the quarks in close confinement are completely free to move about. Part of the nature of quark confinement is that the further you try to force the quarks apart, the greater the force of containment. This is often visualized in terms of the "bag model" of quark confinement.

当介子或重子内部的夸克彼此靠近时，将它们约束在一起的力逐渐减弱；在间距很小时，这种力趋近于零。这意味着夸克在很小的受限区域内可以自由运动。夸克禁闭的另一面是：越想把夸克拉开，所需的力越大。人们常用夸克禁闭的“袋模型”来形象说明这一点。

A potential function which has been successfully used to describe some quark systems is of the form:

已成功用于描述某些夸克系统的势函数形式为：

The quark-quark coupling strength decreases for small values of r, and Rohlf describes this qualitatively as resulting from the penetration of the gluon cloud surrounding the quarks. The gluons carry "color charge" and therefore the penetration of the cloud would reduce the effective color charge of the quark.

当r取小值时，夸克-夸克耦合强度减小，Rohlf定性地将这种现象描述为由于夸克周围的胶子云的渗透所致。胶子携带“颜色电荷”，因此胶子云的渗透会降低夸克的有效颜色电荷。

Another approach to asymptotic freedom is to use a variable strong force coupling constant which depends upon the wavelength of the quark. An expression which comes from quantum chromodynamics is:

另一种实现渐近自由的方法是使用一个依赖于夸克波长的强相互作用耦合常数。来自量子色动力学的一个表达式为：

The nature of this relationship is that it gives a value of about 1 for the coupling constant at the radius of a proton, and this is the value conventionally used to describe the strength of the strong interaction within nuclei. When the proton is penetrated to a radius corresponding to an energy of 1 TeV, the coupling constant is down to about 0.1, another manifestation of asymptotic freedom.

这种关系的性质是，在质子的半径处，耦合常数约为1，这个值通常用于描述核内强相互作用的强度。当质子被穿透到对应1 TeV能量的半径时，耦合常数下降到约0.1，这是渐近自由的另一个表现。

Index

Particle concepts

Reference
Rohlf
Ch. 17,18

索引粒子概念参考Rohlf第17、18章

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夸克禁闭模型有助于理解为什么我们尚未观测到孤立的夸克。如果一个粒子的构成夸克获得足够的能量，它会产生一个介子喷注，因为施加给夸克的能量用于产生夸克-反夸克对。