Institut für Kernphysik, Johannes Gutenberg Universität Mainz, Germany.
Phys Rev Lett. 2011 Aug 12;107(7):072002. doi: 10.1103/PhysRevLett.107.072002. Epub 2011 Aug 10.
We present a formula that allows one to calculate the pion form factor in the timelike region 2m(π) ≤ √(s) ≤ 4m(π) in lattice QCD. The form factor quantifies the contribution of two-pion states to the vacuum polarization. It must be known very accurately in order to reduce the theoretical uncertainty on the anomalous magnetic moment of the muon. At the same time, the formula constitutes a rare example where, in a restricted kinematic regime, the spectral function of a conserved current can be determined from Euclidean observables without an explicit analytic continuation.
我们提出了一个公式，可用于计算在格点 QCD 中时变区域 2m(π) ≤ √(s) ≤ 4m(π) 内的π介子形状因子。形状因子量化了双π态对真空极化的贡献。为了降低μ子反常磁矩的理论不确定性，必须非常准确地知道它。同时，该公式构成了一个罕见的例子，即在受限的运动学区域内，可以从欧几里得可观测量中确定守恒电流的谱函数，而无需进行显式解析延拓。
