Progress towards a precise ab initio determination of parton structure of hadrons

这项提议是我们合作的长期努力的一部分，目的是大幅提高晶格QCD对强子结构物理的有用性。格子QCD要求解析地将时间延续到虚构时间。这产生了令人不快的结果，即只有在时间上是局部的场相关器才能被直接评估。它们与算符乘积展开与夸克和胶子分布函数的矩有关。不幸的是，在实践中，由于数值噪声和操作符混合，只能确定前几个时刻，这不足以满足大型强子对撞机(欧洲核子研究中心，瑞士)、北京北极子中心(美国)以及计划在中国进行的CEPC和EICC的高亮度实验的需要。几年前，已经提出了几种替代方法，这些方法有可能从根本上改变这种情况，首先是纪万昌教授建议的LaMET。过去已经提出了相关建议，但没有产生实际后果。这一点现在已经改变了。在“格子部分协作”(LPC)中，我们对LaMET进行了系统的测试和改进，扩大了它的适用性。到目前为止，这主要发生在德国方面的SFB/TRR-55“来自晶格QCD的强子物理学”中，该计划将于2020年6月30日结束。这一建议的目的是利用我们计划推导的CLS组态和双圈匹配函数，仔细确定核子和介子DAS扭度-2pdf的系统不确定度。

This proposal is part of a long term effort of our collaboration to substantially improved the usefulness of Lattice QCD for hadron structure physics. Lattice QCD requires to analytically continue time to imaginary time. This has the unpleasant consequence that only field correlators which are local in time can be straightforwardly evaluated. These are related by operator product expansion to moments of quark and gluon distribution functions. Unfortunately, in practice only the leading few moments can be determined due to numerical noise and operator mixing, which is insufficient for the needs of high luminsity experiments as performed/planned at LHC (CERN, Switzerland), the EIC at BNL (USA), as well as the CEPC and EicC planned in China. A few years ago several alternative approaches have been suggested, which have the potential to change this situation fundamentally, starting with LaMET suggested by Prof. Ji. Related suggestions were already made in the past but without practical consequences. This has changed now. Within the "Lattice Parton Collaboration" (LPC) we systematically test and improve LaMET and expand its applicability. So far this happened on the German side primarily within SFB/TRR-55 "Hadron Physics from Lattice QCD" which will end June,30 2020. This proposal aims at a careful determination of the systematic uncertainties for twist-2 pdfs of the nucleon and meson DAs using CLS configurations and two-loop matching functions which we plan to derive.