J/Psi Photoproduction off the proton and neutron with CLAS12

在量子色动力学（QCD）的框架内，从夸克和胶子的自由度来理解强子的结构和相互作用，是现代核/强子物理学的主要目标。进一步探索这些基本性质的一个重要工具是研究具有强子物质的重夸克子。重夸克的产生直接探测了核子中的局部色子场（胶子场），可以揭示诸如它们的空间分布（构建核子内部成分的图像）、系统内动量转移的响应（图像如何随能量变化）以及与价夸克（赋予核子电荷等属性的夸克）的相关性等特性。重夸克的第一态是由束缚粲-反粲组成的双夸克体系，即J/Psi介子。随着杰斐逊实验室可用的光束能量升级到12GeV，以及b大厅在线的新探测器系统CLAS12，现在可以研究j /Psi的光电生产。在高能下有相当数量的J/Psi光生产数据，但在阈值附近没有数据。考虑到高能和近阈值区域之间的动力学变化，最近在CLAS12的质子和氘靶上进行的两个实验将在“现实世界”的强子能量尺度上提供关于核子内胶子场的独特信息。除了对这些基本QCD自由度的研究之外，最近在大型强子对撞机中发现了五夸克（5夸克）结构，这重新引起了人们对调和子阈值区域的兴趣。这些状态，如果它们存在，在上述测量的可用能量范围内，这些数据有可能为支持或反对这些状态提供令人信服的证据。此外，CLAS12处于独特的位置，可以提供中子（在氘内）产生的测量结果，从而检查对于任何“新”共振主张而言，同位旋不变性成立的必要性。简单地说，如果一个五夸克共振产生衰减到J/Psi和质子，那么也必须存在一个衰减到J/Psi和中子的五夸克共振。项目目前的目的和目标是：通过对电子-正电子对的分析，研究CLAS12探测器系统的粒子识别效率。开发一个基于数据的标准切割分析，开发一个机器学习算法来复制和验证上述标准方法。机器学习的开发在强子物理社区仍处于起步阶段，任何这样的发展将为未来的分析项目提供有价值的指导。最终提取出J/ psi质子和J/Psineutron的截面（产生概率）。该项目将在CLAS合作杰弗逊实验室进行。

Understanding hadronic structure and interactions in terms of quark and gluon degrees of freedom,within the framework of Quantum Chromodynamics (QCD), is the main goal of modernnuclear/hadron physics. An important tool to further explore these fundamental properties is thestudy of heavy quarkonia with hadronic matter. The production of heavy quarkonia directly probesthe local colour (gluonic) fields in the nucleon and can reveal properties such as their spatialdistribution (building a picture of the internal components of the nucleon), the response tomomentum transfer within the system (how does the picture vary with energy) and the correlationwith valence quarks (the quarks that give the nucleon its properties such as charge).The first state of heavy quarkonia is the two quark system comprising of a bound charm-anti-charmpair, namely the J/Psi meson. With the available beam energy at Jefferson Lab now upgraded to 12GeV and a new detector system, CLAS12 in Hall-B on-line, the photo- and electroproductionofJ/Psi can now be studied. There is a considerable amount of J/Psi photoproduction data at highenergies but no data near threshold. Given the considerable change in dynamics between highenergy and the near-threshold regions, two recent experiments carried out on a proton and adeuterium target at CLAS12 will provide unique information on the gluonic fields within thenucleon at "real-world" hadronic energy scales.In addition to the studies of these fundamental QCD degrees of freedom, recent claims of thediscovery of pentaquark (5 quark) like structures from the LHCb have renewed interest in thischarmonium threshold region. These states, should they exist, are within the energy range availablein the above measurements and this data has the potential to provide compelling evidence for oragainst such states. Furthermore, CLAS12 is in the unique position to provide measurements fromproduction off a neutron (within deuterium) and thus check the necessity for isospin invariance tohold true regarding any "new" resonance claims. In simple terms, if a pentaquark resonance isproduced decaying to a J/Psi and proton, then one must also exist which decays to J/Psi and aneutron.The project aims and objectives are currently defined to:Study the particle identification efficiency of the CLAS12 detector system through the analysis ofelectron-positron pairs.Develop a standard cuts based analysis for the dataDevelop a machine learning algorithm to replicate and verify the above standard approach. Theexploitation of machine learning is still in its infancy within the hadronic physics community andany such development will provide valuable guidance for future analysis projects.Ultimately extract the cross-sections (the production probabilities) of J/Psi-proton and J/Psineutron.The project will be undertaken within the CLAS Collaboration at Jefferson Lab.