Have He Isotopes in Muonic Atoms Been Fully Explored?

[Khashishi]

Casual searches for muonic atoms brings up various experiments on muonic hydrogen. The physics of this atom is fairly simple because the muon is just a heavier version of an electron. Has anyone studied atoms with both an electron and a muon around a nucleus, such a helium isotope? In this case, I suppose the excitation states would become pretty interesting, since the electron and muon are allowed to overlap.

 

[mfb]

All experiments about myon-catalyzed fusion should have gotten those atoms, so maybe they are a good starting point. I would expect that the electron gets hydrogen-like energy levels, as the muon is so close to the nucleus.