TheB¯→Xsγphoton spectrum

The photon energy spectrum in inclusive weak radiative $\overline{B}\to X_s\gamma$ decay is computed to order ${\alpha }_s^2{\beta }_0.$ This result is used to extract a value for the heavy quark effective theory (HQET) parameter $\overline{\Lambda }$ from the average $〈1-{2E}_{\gamma }{/m}_B〉,$ and a value of the parameter ${\lambda }_1$ from $〈(1\mathrm{}-{2E}_{\gamma }{/m}_B{)}^2〉.$ An accurate measurement of $〈1-{2E}_{\gamma }{/m}_B〉$ can determine the size of the nonperturbative contributions to the ${\rm Y}\mathrm{}\left(1S\right)\mathrm{}$ mass which cannot be absorbed into the b quark pole mass.