标题： 核子和原子核中反夸克的味不对称性 显示英文标题

标题： Flavour asymmetry of antiquarks in nucleon and nucleus

摘要： 多年来，全面的实验已经表明一个事实，即核子，如质子和中子，不仅由以前简单组成图像中认为构成核子的“价”上夸克和下夸克组成，还由“海”夸克组成，这些海夸克可以是任何其他味。 然而，目前还不清楚海夸克是如何在核子内部产生的。 自20世纪90年代以来，对高能氘核（由一个质子和一个中子组成）的测量表明，基于质子-中子同位旋对称性的假设和氘核的小核效应，质子中的反下夸克贡献高于反上夸克。 因此，海夸克被认为是通过某种味不对称机制产生的。 在这里，我们报告了一项对一系列纯质子相互作用的新测量的分析，这些测量摆脱了这些假设，意外地显示反下夸克成分与反上夸克相当。 这似乎表明之前观察到的不对称性是由于氘核中的未知核效应造成的，而不是由于反夸克之间的差异。 我们认为这项工作将成为在高能尺度上研究核结构的重要新发现，并激发实验和理论研究，因为它现在看起来与过去建立的理解根本不同。 显示英文摘要

摘要： Over the years, comprehensive experiments have shown a fact that the nucleons, such as the proton and neutron, are formed by not only the "valence" up and down quarks which were thought to comprise the nucleons in a simple constituent picture, but also "sea" quarks which can be any other flavour. However, it is still unknown how sea quarks are generated inside the nucleons. Since 1990s, measurements on high energy deuterons (formed by a proton and a neutron) indicated that the anti-down quark contribution was higher than the anti-up quark in the proton, based on the assumptions of the proton-neutron isospin symmetry and a small nuclear effect of the deuteron. Henceforth, sea quarks are considered to be generated via some flavour-asymmetrical mechanisms. Here we report an analysis on a series of new measurements from pure proton interactions which are free from those assumptions, unexpectedly showing that the anti-down quark component is rather consistent with the anti-up quark. It appears to be evidence that the previously observed asymmetry was caused by an unknown nuclear effect in the deuteron, rather than by a difference between antiquarks. We anticipate this work to be an essential new discovery and a motivation for studying nuclear structure, both experimentally and theoretically, at high energy scales, as it now appears fundamentally different from our understanding established in the past.