New upper limit for the branching ratio of the ${\mathrm{\Omega }}^{\mathrm{-}}$→${\mathrm{\Xi }}^{\mathrm{-}}$γ radiative decay

We have searched for the rare hyperon radiative decay ${\mathrm{\Omega }}^{\mathrm{-}}$→${\mathrm{\Xi }}^{\mathrm{-}}$ γ, using the Fermilab Proton Center 375 GeV/c charged hyperon beam. Our measurement of the ${\mathrm{\Omega }}^{\mathrm{-}}$ beam fraction at 13.6 m from production is (4.8 ± 0.4)×${10}^{\mathrm{-}5}$. No signal was found and we determine a new upper limit of 4.6×${10}^{\mathrm{-}4}$ at 90% C.L. for the ${\mathrm{\Omega }}^{\mathrm{-}}$→${\mathrm{\Xi }}^{\mathrm{-}}$ γ branching ratio.