g Factor of Boronlike Tin

In the experiment, the g factor of boronlike Sn45+118 has been measured with a 0.5 ppb uncertainty. This is the first high-precision measurement of the g factor of a heavy boronlike ion. The measured value of 0.6 447 038 265(4) is consistent with the presented state-of-the-art theory calculations, which predict a value of 0.64 470 29(8). So far, the only boronlike ion of which the g factor was measured with high precision has been Ar13+40. The measurement presented here therefore tests quantum electrodynamics as well as many-electron interactions at much higher Z. Furthermore, we discuss the potential for an independent determination of the fine-structure constant α, which can be achieved with a specific difference of g factors, combining the presented results with the recent electron g-factor measurement of hydrogenlike tin. Published by the American Physical Society 2025