On the nuclear dependence of the μ−→e− conversion branching ratio

The variation of the coherent branching ratio Rμe (ratio of the μ−→e− reaction rate divided by the total muon-capture rate) through the periodic table is studied by using exact muon wave functions. It was found that, by using very heavy nuclei (e.g. 197Au, the SINDRUM II target) as μ−→e− conversion stopping targets, the above ratio is favored by a factor of about four to five than by using light ones (e.g. 48Ti, chosen as PRIME target).