Calculation of the semileptonic decay width of theΛbbaryon

We extend the approach based on light-cone expansion and heavy quark effective theory to inclusive semileptonic decay of an unpolarized $b$-flavored hadron. It is applied to calculate the semileptonic decay width of the ${\Lambda }_b$ baryon and its ratio to that of the $B$ meson. We obtain ${\Gamma }_{\mathrm{SL}}\left({\Lambda }_b\right)=(51\mathrm{}\pm 9)|V_{\mathrm{cb}}{|}^2$ ${\mathrm{ps}}^{-1}$ and ${\Gamma }_{\mathrm{SL}}\left({\Lambda }_b\right)/{\Gamma }_{\mathrm{SL}}\mathrm{}\left(B\right)=1.052\mathrm{}\pm 0.006$. From the latter, the semileptonic branching fraction for ${\Lambda }_b$ is predicted to be $(8.7\mathrm{}\pm 0.7)\%$.