Measurement of Inclusive Radiative $B$-Meson Decays with a Photon Energy Threshold of 1.7 GeV

Using $605{\mathrm{fb}}^{-1}$ of data collected at the ${\rm Y}(4S)$ resonance we present a measurement of the inclusive radiative $B$-meson decay channel, $B\to X_s\gamma$. For the lower photon energy thresholds of 1.7, 1.8, 1.9, and 2.0 GeV, as defined in the rest frame of the $B$ meson, we measure the partial branching fraction and the mean and variance of the photon energy spectrum. At the 1.7 GeV threshold we obtain the partial branching fraction $\mathrm{BF}(B\to X_s\gamma )=(3.45\pm 0.15\pm 0.40)\times {10}^{-4}$, where the errors are statistical and systematic.

Figure 1

The extracted photon energy spectrum of $B\to X_{s,d}\gamma$ in the (a) MAIN and (b) LT stream before any correction for signal acceptance is applied; and (c) displays their average after correction by the selection efficiency. The two error bars for each point show the statistical and the total error. The total error is a sum in quadrature of the statistical and systematic errors, where the latter are correlated between bins. The LT and MAIN streams refer to the set of selection criteria that do and do not include the lepton tag criterion, respectively.