In the framework of the soft-collinear effective theory, we demonstrate that the leading-power heavy-to-light baryonic form factors at large recoil obey the heavy quark and large energy symmetries. Symmetry breaking effects are suppressed by ${ \Lambda}/m_{ b}$ or $\Lambda/E$, where $\Lambda$ is the hadronic scale, $m_b$ is the $b$ quark mass and $E\sim m_b$ is the energy of light baryon in the final state. At leading order, the leading power baryonic form factor $\xi_{ \Lambda,p}(E)$, in which two hard-collinear gluons are exchanged in the baryon constituents, can factorize into the soft and collinear matrix elements convoluted with a hard-kernel of order $\alpha_s^2$. Including the energy release dependence, we derive the scaling law $\xi_{ \Lambda,p}(E)\sim \Lambda^2 /E^2$. We also find that this form factor $\xi_{ \Lambda}(E)$ is numerically smaller than the form factor governed by soft processes, although the latter is formally power-suppressed.
Categories: hep-ph