Measurement of deep exclusive meson-production in electron scattering off a neutron using CLAS12 at Jefferson Lab

该项目是通过中子产生介子的实验测量来研究核子结构。这项实验由Clas Collaboration进行，将于2019年在美国杰斐逊实验室B厅进行。它将使用实验室的10.6GeV极化电子束、CLAS12探测器和一个固定的氢靶。深度排他性介子产生是一个过程，在这个过程中，高能电子从核子内部的部分粒子(在本实验中可用的能量下，它们是价夸克)散射，从而产生高动量介子。对由于光束或靶的不同偏振态引起的截面和不对称性的分析携带了有关核子中部分子的空间和动量分布的信息。具体地说，深度虚化介子的产生产生了关于广义部分子分布(GPD)的信息，这些信息将纵向部分子动量与它们的横向位置联系起来。因此，对GPD的测定使核子的3D断层成像成为可能。GPD还携带有关核子自旋组成的信息(未知，超出夸克本征自旋的贡献部分)。GPD最近还与核子内的压力分布联系在一起，为研究核子结构开辟了一条全新的途径。该项目很可能将重点放在分析中子产生中性子的深度虚拟中子束-自旋不对称性。从中子产生负的介子也在考虑之中(在这种情况下，反冲核子是一个质子)。学生项目将涉及杰斐逊实验室的数据采集、中央中子探测器的校准和提取可观测数据的数据分析(S)。目标是在论文项目接近尾声时出版。分类活动类型与所列活动的相关性百分比(以5的倍数表示)，总计为100%：-开发和实验%100%-对新仪器、设施或技术的投资-设施的操作和维护-理论学生分类请选择以下选项之一来说明学生的总体分类：-天文学-核物理。X粒子天体物理学

The project is the study of nucleon structure through the experimental measurement of meson electro-production from the neutron. The experiment, run by the CLAS collaboration, will take place in Hall B of Jefferson Lab, USA, in 2019. It will use the lab's 10.6 GeV polarised electron beam, the CLAS12 detectors and a fixed deuterium target.Deep exclusive meson-production is a process in which a high energy electron scatters from the partons (at the energies available in this experiment they are valence quarks) inside the nucleon, and a high-momentum meson is produced as a result. Analysis of the cross-sections and asymmetries due to different polarisation states of the beam or target carry information about spatial and momentum distributions of the partons in the nucleon. Specifically, deeply virtual meson production yields information on Generalised Parton Distributions (GPDs), which correlate longitudinal parton momentum to their transverse position. As such, determination of GPDs enables 3D, tomographic imaging of the nucleon. GPDs also carry information on the composition of nucleon spin (unknown, beyond the fraction contributed by the intrinsic spin of quarks). The GPDs have recently also been linked to pressure distributions within the nucleon, opening an entirely new way of studying nucleon structure.The project will most likely focus on the analysis of beam-spin asymmetry in the deeply virtual production of neutral pions from the neutron. The production of a negative pion from the neutron is also under consideration (with the recoiling nucleon being a proton in this case). The student project will involve data-taking at Jefferson Lab, calibration of the Central Neutron Detector and analysis of the data for the extraction of the observable(s). The aim is a publication towards the end of the thesis project. ClassificationsType of activityAssign % relevance (in multiples of 5) to the activities listed, totalling 100%:- Exploitation and experiment %100- Investment in new instrumentation, facilities or techniques- Operation & maintenance of facilities- TheoryStudent classificationPlease select one of the following options to indicate the overall classification of the student:- Astronomy- Nuclear Physics. X- Particle Astrophysics