First Measurement of the Rate for the Inclusive Radiative Penguin Decay $\mathit{b}\to \mathit{s}\mathit{\gamma }$

We have measured the inclusive $b\to s\gamma$ branching ratio to be $(2.32\pm 0.57\pm 0.35)\times {10}^{-4\mathrm{}}$, where the first error is statistical and the second is systematic. Upper and lower limits on the branching ratio, each at 95% C.L., are $B(b\to s\gamma )<4.2\mathrm{}\times {10}^{-4\mathrm{}}$ and $B(b\to s\gamma )>1.0\mathrm{}\times {10}^{-4\mathrm{}}$. These limits restrict the parameters of extensions of the standard model.