Inclusive Measurement of the Photon Energy Spectrum in $b\to s\gamma$ Decays

We report a fully inclusive measurement of the flavor changing neutral current decay $b\to s\gamma$ in the energy range $1.8\mathrm{G}\mathrm{e}\mathrm{V}\le E_{\gamma }^{*}\le 2.8\mathrm{G}\mathrm{e}\mathrm{V}$, covering 95% of the total spectrum. Using $140\mathrm{f}{\mathrm{b}}^{\mathrm{-}\mathrm{1}}$, we obtain $\mathcal{B}(b\to s\gamma )=(3.55\pm {0.32}_{-0.31-0.07}^{+0.30+0.11})\times {10}^{-4}$, where the errors are statistical, systematic, and from theory corrections. We also measure the first and second moments of the photon energy spectrum above $1.8\mathrm{G}\mathrm{e}\mathrm{V}$ and obtain $\langle E_{\gamma }\rangle =2.292\pm 0.026\pm 0.034\mathrm{G}\mathrm{e}\mathrm{V}$ and $\langle E_{\gamma }^2\rangle -\langle E_{\gamma }{\rangle }^2=0.0305\pm 0.0074\pm 0.0063{\mathrm{G}\mathrm{e}\mathrm{V}}^2$, where the errors are statistical and systematic.

Figure 1

Photon energy spectra in the ${\rm Y}(4S)$ frame.

Figure 2

Efficiency-corrected photon energy spectrum. The two error bars show the statistical and total errors.