Studies of Nucleon Structure and Medium Modifications with Electroweak Probes

这项研究的目的是提供关于自由质子和中子（核子）以及原子核内束缚的质子和中子的基本结构的重要实验信息。 当轻子从具有大动量转移的核子散射时，该过程可以在微扰QCD中描述，其中散射发生在具有良好定义的纵向动量分布的渐近自由夸克上。 另一方面，夸克被限制在介子和重子中，在低动量转移时，这些复合粒子是有效的自由度。 这项研究的一个重点是更好地了解这些制度之间的过渡。 特别是，这笔赠款将支持精确测定质子到大动量转移的磁弹性形状因子的工作，以研究向微扰标度的过渡，此外还将测量大Bjorken-x下质子和氘核的F_2结构函数，其中大部分核子动量由单个价夸克携带。 前一个实验将在Jefferson Lab实验大厅A进行，后者将在大厅C进行。此外，这项研究将研究核子在核介质中的变化，目前还没有普遍接受的物理模型。 虽然在电子和μ子散射中已经进行了许多关于在原子核中测量的结构函数与在氘核上测量的结构函数之比的研究，但实际上没有中微子散射的实验数据。 这些数据将提供重要的测试模型的介质修改，并将是重点即将MINERvA中等能量束运行，而成功结束的低能量运行的持续分析主要集中在弹性散射和共振的生产。从更广泛的角度来看，该项目旨在通过新的实验数据进一步阐明普通物质的核成分结构。 虽然量子色动力学（QCD）已被公认为强相互作用理论，它负责将组分夸克和胶子限制在组成普通物质的复合强子中，但由此产生的结构仍然存在许多问题。这些研究将通过电磁相互作用，利用Jefferson实验室的电子束和弱相互作用，在费米实验室的MINERvA实验中利用中微子束。杰斐逊实验室的两个实验预计将是加速器能量升级后的第一批实验。 这将利用该小组的重要专业知识来调试A厅和C厅，以支持这些实验，这也将广泛支持更大的杰斐逊实验室核物理计划。 预计这一研究计划还将解决下一代物理学研究人员培训的关键需求，其中非洲裔美国人和妇女都明显不足。

The objective of this research is to provide important experimental information on the fundamental structure of both free protons and neutrons (nucleons) and those bound inside the atomic nucleus. When scattering leptons from nucleons with large momentum transfer the process can be described within perturbative QCD in which the scattering takes place on an asymptotically free quark with a well defined longitudinal momentum distribution. On the other hand, the quarks are confined inside mesons and baryons, and at low momentum transfer it is these composite particles which are the effective degrees of freedom. One focus of this research is on better understanding the transition between these regimes. In particular, this grant will support work on a precision determination of the magnetic elastic form factor of the proton to large momentum transfer to study the transition to perturbative scaling, in addition to a measurement of the F_2 structure function of the proton and deuteron at large Bjorken-x, for which most of the nucleon momentum is carried by a single valence quark. The former experiment will be performed in Jefferson Lab experimental Hall A and the latter in Hall C. In addition, this research will study the modification of the nucleons in the nuclear medium, for which no generally accepted physics model currently exists. While many studies of the ratio of structure functions measured in nuclei to those on the deuteron have been performed in electron and muon scattering, practically no experimental data exists for neutrino scattering. Such data would provide important tests of models of medium modifications and will be the focus of the upcoming MINERvA medium energy beam run, while the continuing analysis of the successfully concluded low energy run is primarily focused on elastic scattering and resonance production. From a broader perspective, this project aims to further elucidate the structure of the nuclear constituents of ordinary matter via new experimental data. While, Quantum Chromodynamics (QCD) has been accepted as the theory of the strong interaction, which is responsible for confining the constituent quarks and gluons into the composite hadrons which make up ordinary matter, many questions of the resulting structure still remain.These studies will be performed with complementary probes via the electromagnetic interaction, utilizing the electron beam at Jefferson Lab, and the weak interaction, utilizing a neutrino beam in the MINERvA experiment at Fermilab.Both Jefferson Lab experiments are expected to be among the first performed after the energy upgrade of the accelerator. This will leverage the significant expertise of this group to the commissioning of both Hall A and Hall C in support of these experiments, which will also broadly support the larger Jefferson Lab nuclear physics program. It is expected that this research program will also address a critical need in the training of the next generation of researchers in physics, where African-Americans and women are both significantly under-represented.