Meson Transition Form Factors (Project TFF)

两个实光子或虚光子与强子物质的相互作用用跃迁形式因子（TFFs）来描述。这些不仅提供了有关强子内部结构的信息，而且也是进一步约束强子对μ子异常磁矩的光-光贡献的不确定性的必要输入。TFF项目的目的是利用实验和理论努力的协同作用提供信息。A2/MAMI实验的高精度测量将提供介子达里茨衰变的类时间TFFs的世界领先信息。BESIII实验将在双光子聚变反应中产生单介子和多介子系统中获得类空TFFs的补充信息。利用基于实光子色散分析的信息、数据驱动的现象学方法，将其扩展到虚光子和更高介子多重度，以提供对相关标量、张量和轴向介子的访问。此外，在晶格上的从头计算将提供单介子的双虚TFFs信息，这在实验中是具有挑战性的。最终，TFF项目获得的数据和开发的工具可以通过研究介子极化率来从不同的角度了解强子结构。

The interaction of two real or virtual photons with hadronic matter is described by transition form factors (TFFs). These do not only provide information on the internal structure of the involved hadrons, but are also necessary input to further constrain the uncertainties of the hadronic Light-by-Light contribution to the anomalous magnetic moment of the muon. The aim of Project TFF is to provide the information exploiting synergies of experimental and theoretical efforts. High-precision measurements at the A2/MAMI experiment will provide world-leading information on time-like TFFs from meson Dalitz decays. Complementary information on space-like TFFs will be obtained at the BESIII experiment in two-photon fusion reactions producing single mesons and multi-meson systems. Making use of the information, data-driven phenomenological approaches, which have already been developed based on dispersive analysis for real photons are extended to virtual photons and higher meson multiplicities in order to provide access to the relevant scalar, tensor and axial mesons. In addition, ab-initio calculations on the lattice will provide the information on double-virtual TFFs of single mesons, which is challenging to obtain from experiments. Eventually, the data obtained and tools developed in project TFF can be used to access hadron structure from a different angle by studying pion polarizabilities.