Results from recent searches for muonium-- antimuonium conversion and future perspectives

TL;DR

This paper reviews recent experimental searches for muonium-antimuonium conversion, discusses the theoretical implications of such processes, and explores future experimental prospects to detect potential new physics beyond the Standard Model.

Contribution

It provides an overview of recent experimental results and future perspectives on muonium-antimuonium conversion searches, highlighting their significance for probing new physics.

Findings

No positive detection of muonium-antimuonium conversion so far

Current experiments set stringent limits on the conversion probability

Future experiments aim to improve sensitivity to potential signals

Abstract

A positive muon ($\mu^+$) and an electron ($e^-$) form the the hydrogen-like muonium atom ($M$=$\mu^+ e^-$). Since it consists of two leptonic particles which are according to present knowledge point-like, accurate calculations of its level energies can be performed in the framework of standard theory. In particular, the theoretical description of this system is possible almost exclusively by Quantum Electrodynamics (QED) which has been verified in various very high precision experiments. Due to the close confinement of the bound state the muonium atom renders in addition the possibility for sensitive searches for electron--muon interactions not included in the standard model. Such exotic processes could affect the energy of the quantum states at a level of the same order of magnitude as the precision achievable in modern spectroscopic experiments.Oscillations between muonium and antimuonium ($\bar{M}$=$\mu^- e^+$) would violate separate additive lepton number conservation which is a purely empirical law.