New higher precision measurements of the hyperfine Zeeman transitions in the ground state of muonium have been performed with use of the high-stopping-density surface \i + beam at the Clinton P 0 Anderson Meson Physics Facility. The results are Ay = 4 463-302.88(16) kHz (0.036 ppm) and n^/np^ 3.183 3461(11) (0.36 ppm). The current theoretical value of Ay agrees well with experiment within the 0.77-ppm error of Ay t^eor , which is due principally to inaccuracy in evaluation of the nonrecoil radiative correction term. The most precise current value of m n /m e is obtained from our value of \ij\x p ,

In this work, the KLL dielectronic recombination (DR) resonant strengths of He-through to O-like Xe ions were studied, both through experiment and calculation. The experiments were done using a fast electron beam-energy scanning technique at the Shanghai electron beam ion trap. The calculations were done by using the flexible atomic code (FAC), in which the relativistic configuration interaction (RCI) method was employed. For the total resonant strengths, the present experimental and theoretical results for He-, Be-, B-, C-, N-, and O-like Xe ions agree within experimental uncertainties (about 9%). But the experimental result for Li-like Xe is 14% higher than the calculation. The present FAC calculations of the total DR strengths were compared with the available previous calculations, using RCI or multiconfiguration Dirac-Fock (MCDF) methods, and the agreement was very good. In this work, some intermediate-state resolved KLL DR strengths were also obtained and compared with theoretical results, and more discrepancies were revealed.

We report the results of a measurement of the Lamb shift in the n =2 state of muonium. Muonium atoms in the metastable 2S state were produced by the beam-foil method and the formation rate was determined by observation of the Ly-a photons emitted when the metastable atoms were quenched in a static electric field. The Lamb shift (4'&") was measured through observation of the microwave-induced 2'S&&2-2'P&&2 transition with the result $&"=1042» MHz. This result is in agreement with the current theoretical value.