Baryon-Spectrocopy at BESIII

物理学感兴趣的主要课题之一是物质的组成和结构。尤其是强子，它是质子和中子等夸克和胶子的束束态，对它们的描述是不完整的。量子色动力学(QCD)，即强相互作用理论，能够描述大多数实验。然而，无论是QCD，还是导出的有效理论或晶格QCD计算，都不能完全解释丰富的强子谱。强子的激发光谱反映了与极化率、弹性形状因子和部分子分布互补的基本的强动力学。大多数关于N*和超子共振的数据都是在光电生产中获得的。使用J/ψ衰变来研究这些态提供了必要的补充信息，这些信息对于阐明这些态的性质是必要的，并为理论计算提供了输入。这个项目的目标是分析北京谱仪III上的介子-核子末态。BESIII实验最近将其J/ψ数据集增加了8倍，达到了100亿J/ψ事件的数量。这一独特的J/ψ数据集使我们有机会在一个与光产生完全不同的环境中研究具有高统计量的激发重子。在SFB1044项目S3中，我们开始对两个衰变通道：J/ψ→p anti-pη和J/ψ→anti-pΣ^+KS进行分析。分支组分的测定已经完成，并进入了北京电子科学研究院的内部审查过程，准备发表结果。现在，我们要对这两个衰减通道进行分波分析。对于实验数据的解释，该方法被用来确定重子共振性质，而对模型的依赖性最小。此外，我们还想研究衰变通道J/ψ→p反pη‘。作为下一步，我们计划将研究扩展到衰变通道ψ‘→p anti-pη，ψ’→anti-pΣ^+K_S和ψ‘→p anti-pη’，以便更多地了解激发态ψ‘与J/ψ的区别。同时，通过执行上述分析，我们希望进一步完善基于机器学习软件包TensorFlow的PWA工具TensorWaves。

One of the main topics of interest in physics is the composition and structure of matter. Especially for hadrons, which are bound states of quarks and gluons such as the proton and neutron, the description is incomplete. Quantum chromo dynamics (QCD), the theory of the strong interaction, is able to describe most experimental. However, neither QCD nor derived effective theories or lattice-QCD calculations are able to fully explain the rich hadron spectrum. The excitation spectra of hadrons reflect the underlying strong dynamics complementary to polarizabilities, elastic form factors, and parton distributions. Most data concerning N* and hyperon resonances were taken in photo and electroproduction. Using J/ψ decays to investigate these states provides complementary information which is necessary to shed light on the nature of these states and gives input for theoretical calculations.The goal of this project is the analysis of various meson-nucleon final states in charmonium decays at BESIII. The BESIII experiment has recently multiplied its J/ψ data set by a factor of 8 and reached the number of 10 billion J/ψ events. This unique J/ψ data set gives the opportunity to study excited baryons with high statistics in a completely different environment with respect to photoproduction. Within the SFB1044 project S3 we started to perform the analysis of the two decay channels: J/ψ → p anti-p η and J/ψ → anti-p Σ^+ K_S. The determination of the branching fractions is finished and entered the internal review process at BESIII for the publication of the results. Now, we want to perform a partial wave analysis for these two decay channels. For the interpretation of the experimental data this method is used to determine the baryon resonance properties with minimal model dependence. In addition, we want to investigate the decay channel J/ψ → p anti-p η’. As next step we plan to extend the investigation to the decay channels ψ’ → p anti-p η, ψ’ → anti-p Σ^+ K_S and ψ’ → p anti-p η’ in order to learn more about the differences of the excited ψ’ state in comparison to J/ψ. In parallel, by performing the analysis described above we want to further complete the PWA tool TensorWaves which is based on the machine learning software package TensorFlow.