We find evidence for the semileptonic baryonic decay $B^{-}\to p\overline{p}{\ell }^{-}{\overline{\nu }}_{\ell }$ ($\ell =e$, $\mu$), based on a data sample of 772 million $B\overline{B}$ pairs collected at the $\mathrm{\Upsilon }(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy electron-positron collider. A neural-network based hadronic $B$-meson tagging method is used in this study. The branching fraction of $B^{-}\to p\overline{p}{\ell }^{-}{\overline{\nu }}_{\ell }$ is measured to be $(5.8_{-2.1}^{+2.4}\text{(stat)}\pm 0.9\text{(syst)})\times {10}^{-6}$ with a significance of $3.2\sigma$, where lepton universality is assumed. We also estimate the corresponding upper limit: $\mathcal{B}(B^{-}\to p\overline{p}{\ell }^{-}{\overline{\nu }}_{\ell })<9.6\times {10}^{-6}$ at the 90% confidence level. This measurement helps constrain the baryonic transition form factor in $B$ decays.

• Received 26 August 2013

DOI:https://doi.org/10.1103/PhysRevD.89.011101