The MACS experiment performed at PSI in the 1990s provided an yet unchallenged upper bound on the probability for a spontaneous conversion of the muonium atom, ${\rm M=}$($\rm{\mu^+e^-}$) , into its antiatom, antimuonium ${\overline{\rm{M}} = }$($\rm{\mu^-e^+})$. It comprises the culmination of a series of measurements at various accelerator laboratories worldwide. The experimental limits on the process have provided input and steering for the further development of a variety of theoretical models beyond the standard theory, in particular for models which address lepton number violating processes and matter-antimatter oscillations. Several models beyond the standard theory could be strongly disfavored. There is interest in a new measurement and improved sensitivity could be reached by exploiting the time evolution of the conversion process, e.g., at intense pulsed muonium sources.

中文翻译：

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Muonium-Antimuonium 转换

1990 年代在 PSI 进行的 MACS 实验提供了一个尚未受到挑战的铷原子自发转化概率的上限，${\rm M=}$($\rm{\mu^+e^-}$) ，进入它的反原子，antimuonium ${\overline{\rm{M}} = }$($\rm{\mu^-e^+})$。它包括在全球各个加速器实验室进行的一系列测量的结果。该过程的实验限制为超出标准理论的各种理论模型的进一步发展提供了输入和指导，特别是对于解决轻子数违反过程和物质 - 反物质振荡的模型。一些超出标准理论的模型可能会受到强烈反对。人们对新的测量方法很感兴趣，并且可以通过利用转换过程的时间演变来提高灵敏度，例如，