Measurement of theΣ−Magnetic Moment

We have observed x rays produced in atoms formed by ${\Sigma }^{-}$ hyperons with both lead and uranium nuclei. The fine-structure splitting of the x rays can be used to determine the magnetic moment of the ${\Sigma }^{-}$ particle by a method similar to that used in a recent measurement of the $\overline{p}$ magnetic moment. Although the fine-structure splitting for the ${\Sigma }^{-}$ atom was not distinctly resolved, our measurement can place an upper limit on the fine-structure splitting and hence the magnetic moment. We find that the magnetic moment lies in the range $-1.6<\mu <0.8\mathrm{}$ in nuclear magneton units.