Search of hybrids in multi-meson final states with the GlueX experiment at the ThomasJefferson National Accelerator Facility (JLab)

周围的物质是由质子和中子组成的，也就是所谓的核子。这些粒子由三个夸克组成，它们被强相互作用束缚在核子内部。强相互作用通过胶子传递，胶子具有自相互作用粒子的特性。这就导致了这样一个事实，即夸克和胶子被束缚在所谓的强子内部，不能作为自由粒子被观察到。这种观察被称为约束。已知有两种不同类型的强子：一种是由三个夸克组成的重子，另一种是由夸克-反夸克对组成的介子。甚至最初的出版物也暗示了可能存在额外粒子的事实，例如包含四个夸克的五夸克和包含五个夸克的四夸克。含有胶子贡献的粒子也可能存在，例如，具有夸克-反夸克和胶子的混合介子，甚至是纯胶子状态，即所谓的胶球。在过去的几年里，通过几个实验发现了五夸克和四夸克存在的证据。然而，所有这些状态都包含粲夸克，因此质量更高（大约4 GeV）。关于最轻的夸克，尽管有几个候选，但迄今为止还没有发现奇异态存在的证据。为了阐明这个问题，GlueX实验于去年在美国杰弗逊实验室的CEBAF加速器上进行。GlueX实验具有测量中性和带电衰变粒子的特殊能力，具有较高的角和能量分辨率。这为通过系统地绘制介子谱和寻找混合态来寻找奇异态提供了一个理想的设置。在这个研究期间，我想分析由两个中性介子组成的终态，比如两个埃塔介子。在这些最终状态下，与最低铺层胶球预测的相同的量子数可以用于中间状态。以前已经进行过光生产的测量，然而，他们无法使用如此高能量的光子光束，并达到GlueX实验可能达到的精度和统计数据。此外，线偏振光子被用来激发核子。这允许对数据应用不同的约束，并提供进一步的选项来识别中间状态的量子数。在这个奖学金的范围内，我想了解GlueX实验的实验设置，并了解他们的分析软件。这将使我能够进行我自己的分析，并发挥我以前关于不同最终状态和可观察物的提取的知识。我计划加入GlueX合作，并在未来几年广泛地为他们的项目做出贡献。我在GlueX实验中的工作将有助于寻找包含光介子的奇异态，并有望帮助回答这个问题。

The surrounding matter is build-up of protons and neutrons, the so-called nucleons. These particles are composed of three quarks, which are bound inside the nucleon by the strong interaction. The strong interaction is transmitted by gluons, which have the special feature that they are self-interacting particles. This leads to the fact that the quarks and gluons are bound inside the so-called hadrons and cannot be observed as free particles. This observation is called Confinement. There are two different types of hadrons known: the baryons, which consistent of three quarks, and the mesons, which are build-up of a quark-antiquark pair. Even the first publications hinted to the fact that there might be additional particles, for example penta-quarks containing four quarks and tetra-quarks which include five quarks. Particles containing gluonic contributions could also be possible, for example hybrid mesons with a quark-antiquark and a gluon, or even pure states of glue, the so-called glueballs.During the last years evidence was found by several experiment for penta- and tetra-quarks. However, all of these states contained charm quarks and had therefore higher masses (around 4 GeV). Regarding the lightest quarks, no proof for exotic states could be found so far, even though there are several candidates.To shed light on this question, the GlueX experiment was build-up in the last years at the CEBAF accelerator at Jefferson Lab, USA. The GlueX experiment has the special ability to measure neutral and charged decay particles with a high angular and energy resolution. This poses an ideal setup to hunt for exotic states by systematically map the meson spectrum and search for hybrid states.During this fellowship, I want to analyse final states consisting of two neutral mesons like two eta mesons. With these final states, the same quantum numbers, which have been predicted for the lowest laying glueball, become available for the intermediate states. Measurements with photoproduction have been conducted before, however, they were not able use photon beams of these high energies and achieve such a precision and statistics as it is possible for the GlueX experiment. Additionally, linearly polarized photons are used to excite the nucleons. This allows to apply different constraints to the data and gives further options to identify the quantum numbers of the intermediate states.Within the scope of this fellowship I want to get to know the experimental setup of the GlueX experiment and to understand their analysis software. This will allow me to conduct my own analysis and to exert my previous knowledge about the extraction of different final states and the observables. I plan to join the GlueX collaboration and to extensively contribute to their project in the next years. My work at the GlueX experiment will contribute to the search for exotic states containing light mesons and hopefully help to answer this question.