Mesonic atom

A mesonic atom is an atom with one or more of its electrons replaced by a negative π-meson or μ-meson, bound by electrostatic attraction. Mesonic atoms are one kind of exotic atom. Due to the relatively high mass of mesons compared to electrons, mesons orbit much closer to the atomic nucleus than electrons do. Transitions from s-states of π-mesonic atoms are not observed since the lifetime for capture by the nucleus is much less than the lifetime for a radiative transition. The energy levels of a mesonic atom are approximately the same as those for a corresponding ordinary atom, multiplied by the ratio of the meson mass to the electron mass.

Mesonic atoms have been considered as potentially useful for nuclear fusion at relatively low temperatures and pressures, since the smaller orbit of the meson allows mesonic atoms to approach one another more closely than ordinary electronic atoms. However, the short lifespan of mesonic atoms makes it unlikely that a practical use for muon-catalyzed fusion will be developed at any point in the forseeable future.