Hard Scattering Processes in QCD

量子色动力学（QCD）是强相互作用的微观理论，它使我们能够理解强子，如质子、中子和介子，是如何通过组成量子色动力学的部分子形成的。高能散射过程可以用来探索从高能散射中产生的部分子（夸克和胶子）如何转变为强子。虽然这些过程的各个方面都得到了很好的理解，但仍然存在许多引人注目的谜题。横向单自旋不对称（SSAs）就是这样一个难题。早期的QCD计算预测基本消失效应，但实验显示巨大的SSAs高达40%。尽管经过了几十年的研究，但对量子cd中单自旋不对称的详细理解仍然缺失。在此背景下，本项目将探讨在不同的单自旋不对称中，粒子碎片化所起的作用。研究生和博士后将参与这个非常活跃的领域，在当前强子物理的前沿。该项目将使质子-质子碰撞中产生单强子的横向SSAs的广泛数值研究成为可能，其中一个入射质子的极化垂直于反应平面。这些研究将利用现有的分析结果，这些结果以前是由研究者和他的一个研究生开发的。这项研究不仅有望澄清部分子碎裂是否确实可以解释实验中观察到的巨大的SSAs，而且还有望阐明是否可以同时描述强子碰撞和轻子诱导过程中的SSAs。该项目与托马斯·杰斐逊国家加速器设施、布鲁克海文国家实验室的相对论重离子对撞机以及全球其他加速器设施的实验密切相关。

Quantum Chromodynamics (QCD) is the microscopic theory of the strong interactions and allows us to understand how hadrons, such as the proton, neutron and pion, are formed through partons, the building blocks of QCD. High-energy scattering processes can be used to explore how partons (quarks and gluons) that come out of a high-energy scattering make a transition into hadrons. While various aspects of these processes are well understood, many striking puzzles remain. Transverse single-spin asymmetries (SSAs) represent one such puzzle. Early QCD calculations predicted basically vanishing effects, but experiments revealed huge SSAs up to 40%. Despite decades of research, the detailed understanding of single-spin asymmetries in QCD is still missing. In this context, this project will explore the role played by the fragmentation of partons for different single-spin asymmetries. Graduate students and postdoctoral fellows will be involved in this very active field at the frontier of current hadronic physics.This project will make possible extensive numerical studies of transverse SSAs for single-hadron production in proton-proton collisions, where one of the incoming protons is polarized perpendicular to the reaction plane. These studies will make use of existing analytical results that were developed previously by the investigator and one of his graduate students. Not only is this investigation expected to clarify if parton fragmentation can indeed explain the huge SSAs observed experimentally, but also whether a simultaneous description of SSAs in hadronic collisions and in lepton-induced processes can be obtained. This project is closely related to experiments conducted at the Thomas Jefferson National Accelerator Facility, the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, and other accelerator facilities worldwide.