Parton distributions and fragmentation functions

核子的部分子含量和关于终态部分子碎裂的知识是当今粒子对撞机精确预测的关键因素。在QCD的标准因式分解方法中，它们提供了关于长程部分子动力学的基本信息，这是微扰计算无法获得的。现代QCD理论的一个中心任务是提供这些长程部分(通常是部分子分布和碎裂函数)的精确提取，从实验数据与相应的高阶微扰理论的短程因子(通常是部分子截面)的理论计算中进行比较。对于大多数感兴趣的截面，这些理论预测的典型精度目前在QCD中处于次要的领先数量级(N2LO)，对于完全包容的可观测数据甚至更高。在理论进展和来自深度非弹性散射和大型强子对撞机的现有数据以及对未来EIC的展望的推动下，P2计划提出了一种统一的方法，以在新的精度水平上提供关于非微扰部分子动力学的信息。为此，它结合了关于质子以及较轻和较重原子核中部分子动量分布的所有努力，解决了在有和没有极化的情况下的散射过程，目标碎裂函数，并旨在推动QCD的精确度超过N2LO。因此，该项目与所有其他项目有许多相互关系，要么是通过利用要派生的新结果，要么是通过分享成分。

The parton content of nucleons and knowledge on fragmentation of final state partons are key ingredients in precision predictions at today’s particle colliders. In the standard factorization approach to QCD, they provide the essential information on the long-distance parton dynamics, which is inaccessible to perturbative computations. A central task for modern QCD theory consists of providing precision extractions of these longdistance parts (typically, parton distributions and fragmentation functions) from comparisons of experimental data with the corresponding theoretical calculations of the short-distance factors (typically, partonic cross sections) at high orders of perturbation theory. The typical accuracy of those theoretical predictions is currently at next-to-next-to-leading order (N2LO) in QCD for most cross sections of interest and even higher for fullyinclusive observables. Motivated by the theoretical progress and the available data from deep-inelastic scattering and the LHC and the prospects of the future EIC, project P2 presents a unified approach to deliver information on the non-perturbative parton dynamics at a new level of precision. To that end, it combines all efforts concerning momentum distributions of partons in the proton as well as lighter and heavier nuclei, addresses scattering processes with and without polarization, targets fragmentation functions and aims at pushing the accuracy beyond N2LO in QCD. As such, the project has numerous interrelations to all other projects, either by exploiting new results to be derived or by sharing ingredients.