Abstract
By considering the formation of excited muonic molecular ions [(μ−He)2S+ He]*+ in the triplet state a Σ+3, it is possible to explain the presence of metastable muonic helium levels at late times, observed when negative muons are stopped in a high-pressure (p≥6 atm) helium-gas target at room temperature. A comparison of the different experimental results with the present idea is reported, and measurements to obtain independent checks of this scheme are proposed.