Muon transfer from thermalized muonic hydrogen isotopes to argon

Recent experimental results on the muon exchange from muonic hydrogen to argon show that the reaction rate is energy dependent near 0.1 eV. A muonic hydrogen atom, formed by muon capture in H₂ gas at 15 bars, is thermalized in a few hundreds of nanoseconds. If the muon transfer reaction occurs before that time, the rate is shown to be slightly lower compared to thermalized muonic atoms [λ_pAr=(1.63±0.09)×10¹¹fs^-1]. As an indirect consequence, the muon transfer rate from μp to helium, determined by our group [R. Jacot-Guillarmod and co-workers, Phys. Rev. A 38, 6151 (1988)] is lowered by about 40%. The present value λ_pHe=(0.51±0.19)×10⁸fs^-1 is in good agreement with other experiments. The transfer rate from muonic deuterium to argon shows also an energy dependence. The muon transfer rate to argon from the deuteron is λ_dAr=(0.86±0.04)×10¹¹fs^-1 at room temperature. The intensity patterns of the muonic Lyman series of argon obtained by muon transfer from both hydrogen isotopes are determined and compared with theoretical predictions.