发表机构
Peking University; Collaborative Innovation Center of Quantum Matter; Center for High Energy Physics, Peking University; Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences; University of Connecticut（北京大学; 量子物质协同创新中心; 北京大学高能物理中心; 中国科学院近代物理研究所南方核科学理论中心（SCNT）; 康涅狄格大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究利用格点QCD结合反常PCAC关系，计算超出手征极限的中性π介子双光子衰变的质量修正，得到约1%统计精度的衰变宽度，首次从第一性原理确认π⁰-η-η'混合增强。
AI 中文摘要
中性π介子的双光子衰变在手征极限下由Adler-Bell-Jackiw反常确定，而非零夸克质量会产生几个百分点的修正，为了超出手征极限对量子色动力学（QCD）进行精确检验，必须确定这些修正。我们利用反常PCAC关系，在格点QCD中计算这些修正，将其作为q²=0处精确反常条件的偏差，从而避免了传统方法中受四点函数和手征对数抵消限制的问题。由于修正与轻夸克质量成正比，统计和系统不确定性也相应被抑制，使得精确计算成为可能。在两个近物理的畴壁系综上，我们对衰变宽度分别达到约1%的统计精度，经连续体外推后得到Γ(π⁰→γγ)=8.09(22) eV。衰变振幅的2.3(1.4)%质量修正为正，且由同位旋破缺主导，首次从第一性原理确认了π⁰-η-η'混合增强效应。
英文摘要
The two-photon decay of the neutral pion is fixed in the chiral limit by the Adler-Bell-Jackiw anomaly, while nonzero quark masses induce few-percent corrections that must be determined for precision tests of QCD beyond the chiral limit. Using the anomalous PCAC relation, we compute them in lattice QCD as deviations from the exact anomaly condition at $q^2=0$, thereby avoiding both four-point functions and the cancellation of chiral logarithms that limits conventional approaches. Because the correction is proportional to the light-quark masses, both statistical and systematic uncertainties are correspondingly suppressed, making a precision calculation feasible. On two nearly-physical domain-wall ensembles we achieve $\sim1\%$ statistical precision each for the decay width, obtaining $Γ(π^0\toγγ)=8.09(22) eV$ after continuum extrapolation. The $2.3(1.4)\%$ mass correction to the decay amplitude, positive and isospin-breaking dominated, provides the first ab initio confirmation of the $π^0$-$η$-$η'$ mixing enhancement.
Comments11 pages, 10 figures
