Search forB*→B+γinϒ′′′decays and theB*−Bmass difference

The CUSB detector at the Cornell Electron Storage Ring is used to measure the inclusive photon spectrum at the ${\Upsilon }^{\prime \prime \prime }$ peak at 10.58 GeV. In $\approx 50000 {\Upsilon }^{\prime \prime \prime }$ decays, we do not observe any photon signal from $B^{*}\to B+\gamma$ decays for $20<\mathrm{}{E}_{\gamma }<140\mathrm{}$ MeV. We obtain an upper limit on the branching ratio for ${\Upsilon }^{\prime \prime \prime }\to \mathrm{monochromatic} \gamma +\mathrm{hadrons}$ of 6% to 9% at 90% confidence level. From the lack of a photon signal and the observed width of the ${\Upsilon }^{\prime \prime \prime }$ we deduce that the reconstructed $b$-flavored mesons from ${\Upsilon }^{\prime \prime \prime }$ are most likely the pseudoscalar $B$ mesons and that $M\left(B^{*}\right)-M\left(B\right)\mathrm{}>~30$ MeV.