Hoferichter Martin, Hoid Bai-Long, Kubis Bastian, Lüdtke Jan
Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland.
Helmholtz-Institut für Strahlen- und Kernphysik and Bethe Center for Theoretical Physics, Universität Bonn, 53115 Bonn, Germany.
Phys Rev Lett. 2022 Apr 29;128(17):172004. doi: 10.1103/PhysRevLett.128.172004.
We present an improved standard-model (SM) prediction for the dilepton decay of the neutral pion. The loop amplitude is determined by the pion transition form factor for π^{0}→γ^{}γ^{}, for which we employ a dispersive representation that incorporates both spacelike and timelike data as well as short-distance constraints. The resulting SM branching fraction, Br[π^{0}→e^{+}e^{-}]=6.25(3)×10^{-8}, sharpens constraints on physics beyond the SM, including pseudoscalar and axial-vector mediators.
我们给出了中性π介子双轻子衰变的改进标准模型（SM）预测。圈图振幅由π⁰→γγ的π介子跃迁形状因子确定，对此我们采用了一种色散表示，它纳入了类空和类时数据以及短程约束。由此得到的标准模型分支比，Br[π⁰→e⁺e⁻]=6.25(3)×10⁻⁸，加强了对标准模型之外物理的约束，包括赝标量和轴矢中介粒子。
