标题： π介子到光子的转变形式因子：超出价夸克 显示英文标题

标题： Pion to photon transition form factor: Beyond valence quarks

摘要： 我们利用基于光前量子化的框架（BLFQ）中的硬散射公式，在空间-like区域研究了π介子从基态跃迁到$\pi^0\to\gamma^*\gamma$态的单重虚部跃迁形式因子（TFF）。此形式因子可用pion的扰动可计算的硬散射振幅（HSAs）和光前波函数（LFWFs）来表示。我们通过对光前QCD哈密顿量进行对角化得到pion的光前波函数，该哈密顿量是根据其构成的夸克-反夸克和夸克-反夸克-胶子Fock态以及三维限制确定的。我们在夸克-反夸克Fock态中使用到次领头阶（NLO）的硬散射振幅，并在夸克-反夸克-胶子Fock态中使用到领头阶（LO）的硬散射振幅。在夸克-反夸克Fock态中，NLO修正与夸克-反夸克-胶子Fock态中LO对TFF的贡献处于同一阶。我们发现虽然在大动量转移（$Q^2$）区域夸克-反夸克-胶子Fock态的影响较小，但在低$Q^2$区域它有显著影响。我们的结果显示，在考虑两个Fock态之后，BLFQ框架下的TFF与现有的实验数据非常吻合，特别是在低$Q^2$区域。 显示英文摘要

摘要： We investigate the singly virtual transition form factor (TFF) for the $\pi^0\to\gamma^*\gamma$ process in the space-like region using the hard-scattering formalism within the Basis Light-Front Quantization (BLFQ) framework. This form factor is expressed in terms of the perturbatively calculable hard-scattering amplitudes (HSAs) and the light-front wave functions (LFWFs) of the pion. We obtain the pion LFWFs by diagonalizing the light-front QCD Hamiltonian, which is determined for its constituent quark-antiquark and quark-antiquark-gluon Fock sectors with a three-dimensional confinement. We employ the HSAs up to next-to-leading order (NLO) in the quark-antiquark Fock sector and leading order (LO) in the quark-antiquark-gluon Fock sector. The NLO correction to the TFF in the quark-antiquark Fock sector is of the same order as the LO contribution to the TFF in the quark-antiquark-gluon Fock sector. We find that while the quark-antiquark-gluon Fock sector has minimal effect in the large momentum transfer ($Q^2$) region, it has a noteworthy impact in the low-$Q^2$ region. Our results show that, after accounting for both Fock sectors, the TFF within the BLFQ framework aligns well with existing experimental data, particularly in the low $Q^2$ region.