Isotope dependence of particle-decay rates of muonic molecular ions (d^3,4Heμ)_J=1 below (dμ)_1s-^3,4He threshold

Rates of particle-emitting decay of the resonant state of the muonic molecular ion (dHeμ)_J=1 lying below the (dμ)_1s-He threshold can decay to the d-Heμ scattering state. The resonant state is estimated by scattering calculations with the non-adiabatic coupled-rearrangement-channel method. Strong isotope dependence of the decay rates of (d³Heμ)_J=1 and (d⁴Heμ)_J=1 is predicted, though the calculated radiative decay rates of the states are almost the same. In (d³Heμ)_J=1, the particle decay width is three times larger than the radiative decay width, while the two types of decay widths are almost the same in (d⁴Heμ)_J=1. This results in a strong hindrance of the branching ratio of the radiative decay of (d³Heμ)_J=1 compared with the case of (d⁴Heμ)_J=1. This is consistent with a recent observation of the radiative decay of the two molecular states.