Laser Spectroscopy of Positronium and Muonium

Abstract

The laser spectroscopy of leptonic atoms is of interest because of the simplicity of the atoms. Leptons possess no known structure. Unlike the hydrogen atom with its complicated and poorly understood proton, the behavior of leptonic atoms should in principle be calculable to much greater precision. In the case of muonium, the theoretical uncertainty will be limited by our knowledge of fundamental constants such as m _μ /m_p and α. Given the 72 kHz linewidth of the 1S state due to the 2.2μsec lifetime of the muon, one can ultimately expect a measurement of the 1S–2S splitting better than Δν/ν < 10³ Hz/10¹⁵ Hz = 10⁻¹². In the case of positronium, the 140 nsec lifetime should lead to an ultimate precision of Δν/ν = 10⁻¹¹. Thus, this system provides a unique opportunity for the precise study of a purely leptonic two-body system, and QED corrections to that system. In addition to QED tests, the laser excitation of these atoms could provide thermal, sub-thermal, and eventually cryogenic sources of positrons and muons that can be used in a variety of applications.