Motivated by models proposed to explain the Standard Model anomalies, and the unprecedented $\tau^{+}\tau^{-}$ data to be collected by the Belle~II experiment during the next years, we study the kinematics of tau pair decays and propose a new method to search for lepton flavor violating processes in tau lepton decays to invisible beyond Standard Model particles, such as $\tau \to \ell \alpha$, where $\ell$ is either an electron or a muon, and $\alpha$ is a massive particle that escapes undetected. The new method improves by one order of magnitude the expected upper limit on the $\tau \to \ell \alpha$ production in 3x1 prong tau decays and establishes the possibility of performing this search in 1x1 prong tau decays which has not been previously considered.

中文翻译：

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tau 轻子衰变中超越标准模型不可见粒子搜索的新方法

受用于解释标准模型异常的模型的启发，以及未来几年 Belle~II 实验将收集到的前所未有的 $\tau^{+}\tau^{-}$ 数据，我们研究了 tau 对的运动学衰变并提出了一种新方法来搜索 tau 轻子衰变到标准模型粒子之外的不可见过程中的轻子风味违反过程，例如 $\tau \to \ell \alpha$，其中 $\ell$ 是电子或介子，而 $\alpha$ 是一个大质量的粒子，可以不被发现。新方法将 3x1 prong tau 衰减中 $\tau \to \ell \alpha$ 产生的预期上限提高了一个数量级，并建立了在 1x1 prong tau 衰减中执行此搜索的可能性，这是以前未曾考虑过的.