Fabbrichesi M, Gabrielli E, Mele B
INFN, Sezione di Trieste, Via Valerio 2, 34127 Trieste, Italy.
Physics Department, University of Trieste and NICPB, Rävala 10, Tallinn 10143, Estonia.
Phys Rev Lett. 2017 Jul 21;119(3):031801. doi: 10.1103/PhysRevLett.119.031801.
If dark photons are massless, they couple to standard-model particles only via higher dimensional operators, while direct (renormalizable) interactions induced by kinetic mixing, which motivates most of the current experimental searches, are absent. We consider the effect of possible flavor-changing magnetic-dipole couplings of massless dark photons in kaon physics. In particular, we study the branching ratio for the process K^{+}→π^{+}π^{0}γ[over ¯] with a simplified-model approach, assuming the chiral quark model to evaluate the hadronic matrix element. Possible effects in the K^{0}-K[over ¯]^{0} mixing are taken into account. We find that branching ratios up to O(10^{-7}) are allowed-depending on the dark-sector masses and couplings. Such large branching ratios for K^{+}→π^{+}π^{0}γ[over ¯] could be of interest for experiments dedicated to rare K^{+} decays like NA62 at CERN, where γ[over ¯] can be detected as a massless invisible system.
如果暗光子无质量，它们仅通过高维算符与标准模型粒子耦合，而由动力学混合引起的直接（可重整化）相互作用则不存在，而正是这种相互作用推动了当前的大多数实验搜索。我们考虑无质量暗光子可能的味改变磁偶极耦合在K介子物理中的效应。特别是，我们用简化模型方法研究过程K⁺→π⁺π⁰γ̅的分支比，假设手征夸克模型来评估强子矩阵元。考虑了在K⁰ - K̅⁰混合中可能的效应。我们发现，根据暗区质量和耦合情况，允许高达O(10⁻⁷)的分支比。对于像欧洲核子研究组织的NA62这样致力于罕见K⁺衰变的实验来说，K⁺→π⁺π⁰γ̅如此大的分支比可能会很有意义，在该实验中，γ̅可被探测为一个无质量的不可见系统。
