Using Muons and Protons to Probe the Structure of the Universe

该奖项支持两个独立的实验计划，每个计划的目的都是在最基本的层面上探索我们宇宙的结构。其中一个项目将研究在高能质子-质子碰撞中产生的夸克和胶子如何产生新的夸克和胶子，并最终结合在一起形成组成可见宇宙的粒子。这些研究将阐明量子色动力学的本质，这是一种描述强力的理论，强力是构成粒子物理标准模型的三个基本力之一。另一个项目旨在发现新的力和粒子的信号，这些信号还没有包括在标准模型中。费米国家实验室的G-2实验旨在精确测量Muon的磁性，Muon是一种基本粒子，其特征与电子非常相似，但质量是电子的200倍。这项实验是布鲁克海文国家实验室近20年前进行的早期测量的第二代，它与标准模型的理论计算略有不同。费米实验室测量的第一个结果已经公布，它与早期的测量结果一致，但精度更高。实验和标准模型之间的差异表明，标准模型之外的作用力和/或粒子可能对介子的磁矩有贡献。费米实验室g-2的合作正在分析和收集更多的数据集，目的是进一步减少测量的不确定性，并推动发现水平与标准模型预测的差异。这笔拨款支持的实验将为本科生和研究生提供必要的工具和经验，要么继续他们的基础研究工作，要么进入技术劳动力大军，并将他们解决问题的专业知识运用到包括金融、大数据分析、专利法和医学物理在内的众多领域。获得该奖项资助的本科生将继续有难得的机会体验美国国家实验室进行的科学文化和基础研究。该奖项将支持PI和两名研究生在相对论重离子对撞机上使用高能pp和pa碰撞，从完全重建的喷流中识别的介子、介子和质子的分布中提取纵向和横向动量相关的喷注破碎函数。Pp碰撞中的测量将对胶子碎裂函数提供显著的约束，特别是当pp碰撞中的介子、介子或质子承担了母胶子的大部分动量时。对pp和pa的这些相同碎裂产额的比较，将为夸克和胶子强子化过程如何被核环境改变提供新的见解。在另一个维度上观察这种碎裂，作为粒子相对于喷射轴的动量的函数，可以获得质子中的横向动量分布(TMD)。关于未极化的TMD碎裂函数的信息很少，很大程度上是因为用于测量的轻子-质子碰撞的有限能量使现有数据的解释变得复杂。对TMD碎裂函数的研究是推进我们当前量子色动力学图景的全球努力的重要组成部分，量子色动力学是粒子物理标准模型中强相互作用的形式理论。这笔拨款还将允许PI、一名博士后助理和一名研究生继续他们目前在费米实验室的muon g-2实验中的努力。该奖项反映了美国国家科学基金会的法定使命，通过使用基金会的智力优势和更广泛的影响审查标准进行评估，认为值得支持。

This award supports two separate experimental programs, each aimed at exploring the structure of our universe at the most fundamental level. One program will investigate how the quarks and gluons that are produced in high energy proton-proton collisions spawn new quarks and gluons and eventually combine to form the particles that make up the visible universe. These studies will shed light on the nature of Quantum Chromodynamics, a theory that describes the strong force, one of the three fundamental forces that comprise the Standard Model of Particle Physics. The other program aims to discover signals of new forces and particles that are not yet included in the Standard Model. The g-2 experiment at Fermi National Laboratory aims to precisely measure the magnetic properties of the muon, a fundamental particle with characteristics very similar to the electron, but with 200 times the mass. This experiment is a second generation of an earlier measurement made at Brookhaven National Lab nearly twenty years ago that differs somewhat from the Standard Model theoretical calculations. The first result from the Fermilab measurement has been announced and it agrees with the earlier measurement but with better precision. The discrepancy between the experiments and the Standard Model points to possible contributions to the muon's magnetic moment from Beyond the Standard Model forces and/or particles. The Fermilab g-2 collaboration is in the process of analyzing and collecting additional datasets with the goal of further reducing the uncertainties on the measurement and pushing towards a discovery level discrepancy with the Standard Model predictions. The experiments supported by this grant will provide undergraduate and graduate students with the necessary tools and experience to either continue their work in basic research or to enter the technical workforce and lend their problem-solving expertise to a myriad of fields, including finance, big data analysis, patent law and medical physics. Undergraduate students funded by this award will continue to have the rare opportunity to experience the scientific culture and basic research performed at U.S. National Laboratories.This award will support the PI and two graduate students in using high energy pp and pA collisions at the Relativistic Heavy Ion Collider to extract longitudinal and transverse momentum dependent jet fragmentation functions from distributions of identified pions, kaons and protons inside of fully reconstructed jets. Measurements in pp collisions will provide significant constraints on the gluon fragmentation functions, particularly in the case when the pion, kaon or proton assume a large fraction of the parent gluon's momentum. Comparisons of these same fragmentation yields in pp and pA will provide new insights on how the quark and gluon hadronization process is modified by a nuclear environment. Looking at this fragmentation in yet another dimension, as a function of particle momentum relative to the jet axis, provides access to the transverse momentum distributions (TMD) in the proton. Information about unpolarized TMD fragmentation functions is sparse, largely because the interpretation of the existing data is complicated by the limited energy of the lepton-proton collisions used to make the measurements. Investigation of TMD fragmentation functions is an essential piece of a worldwide effort to advance our current picture of Quantum Chromodynamics, the formal theory of strong interactions within the Standard Model of particle physics. This grant will also allow the PI, a postdoctoral associate and a graduate student to maintain their current efforts in the muon g-2 experiment at Fermilab. Contributions will include the development and tuning of the g-2 GEANT based simulation software package, the evaluation of beam dynamics systematic errors that require simulation and the Q-method precession analysis of data taken in Runs 2 & 3.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.