Geesaman D F, Reimer P E
Argonne Associate of Global Empire, LLC, Argonne National Laboratory, Argonne, IL 60439, United States of America.
Rep Prog Phys. 2019 Apr;82(4):046301. doi: 10.1088/1361-6633/ab05a7. Epub 2019 Feb 8.
The quark and gluon structure of the proton has been under intense experimental and theoretical investigation for five decades. Even for the distributions of the well-studied valence quarks, challenges such as the value of the down quark to up quark ratio at high fractional momenta remain. Much of the sea of quark-antiquark pairs emerges from the splitting of gluons and is well described by perturbative evolution in quantum chromodynamics. However, experiments confirm that there is a non-perturbative component to the sea that is not well understood and hitherto has been difficult to calculate with ab initio non-perturbative methods. This non-perturbative structure shows up, perhaps most directly, in the flavor dependence of the sea antiquark distributions. While some of the general trends can be reproduced by models, there are features of the data that do not seem to be well described. This article discusses the experimental situation, the status of calculations and models, and the directions where these studies will progress in the near future.
五十年来，质子的夸克和胶子结构一直处于密集的实验和理论研究之中。即便对于研究充分的价夸克分布而言，诸如高分数动量下下夸克与上夸克比率的值等挑战依然存在。夸克 - 反夸克对的海量成分大多源自胶子的分裂，并且用量子色动力学中的微扰演化能够很好地描述。然而，实验证实，海夸克存在一个非微扰成分，对此人们尚未充分理解，并且迄今为止，用从头算非微扰方法很难进行计算。这种非微扰结构或许最直接地体现在海反夸克分布的味依赖性上。虽然一些总体趋势可以由模型再现，但数据中的某些特征似乎并未得到很好的描述。本文讨论了实验情况、计算和模型的现状，以及这些研究在不久的将来的发展方向。
