J/Psi Photoproduction off the proton and neutron with CLAS12

在量子色动力学(QCD)的框架内，用夸克和胶子自由度来理解强子的结构和相互作用，是现代核/强子物理的主要目标。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尼亚。重夸克子的产生直接探测核子中的局域色(胶子)场，并能揭示它们的空间分布(建立了核子内部成分的图像)、系统内的响应薄层转移(图像如何随能量变化)以及与价夸克(给予核子电荷等性质的夸克)的关联。重夸克子的第一态是由束缚魅力-反魅力对组成的两个夸克系统，即J/Psi介子。随着杰斐逊实验室的可用束流能量现在升级到12GeV，以及一个新的探测器系统CLAS12 in Hall-B在线，现在可以研究J/Psi的光电产生。在高能区有相当数量的J/Psi光产生数据，但在阈值附近没有数据。考虑到高能区和近临界区之间动力学上的巨大变化，最近在CLAS12的质子和德离子靶上进行的两项实验将提供关于核子内胶子场的独特信息，这些信息是在“真实世界”强子能量尺度上的。除了对这些基本QCD自由度的研究外，最近从LHCB发现了五夸克(5夸克)类结构的声明重新引起了人们对这个查尔蒙临界区的兴趣。这些状态，如果它们存在的话，在上述测量中可用的能量范围内，并且这个数据有可能提供令人信服的证据来支持或反对这些状态。此外，CLAS12具有独特的地位，可以提供从一个中子(在重氢内)产生的测量结果，从而检查同位旋不变性的必要性，以证明任何“新的”共振主张是正确的。简而言之，如果五夸克共振衰变到J/Psi和质子，那么也一定存在衰变到J/Psi和非中子束的五夸克共振。目前，项目的目标和目标定义为：通过电子-正电子对的分析来研究CLAS12探测器系统的粒子识别效率。为数据开发基于标准割集的分析开发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界仍处于初级阶段，任何这样的发展都将为未来的分析项目提供有价值的指导。最终提取J/Psi质子和J/Psine中子的截面(产生概率)。该项目将在Jefferson实验室的Clas协作下进行。

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.