Evidence for Semileptonic B- to p pbar l nubar Decays

Abstract

We find evidence for the semileptonic baryonic decay $B^{-}\to p\bar{p}{\ell }^{-}\bar{\hat{I}}{½}_{\ell }$ ($\ell =e,\hat{I}¼$), based on a data sample of 772 million $B\bar{B}$ pairs collected at the $\hat{I}\yen (4S)$ 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 $B^{-}\to p\bar{p}{\ell }^{-}\bar{\hat{I}}{½}_{\ell }$ 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$\ddot{I}ƒ$, where lepton universality is assumed. We also estimate the corresponding upper limit: $\mathcal{B}(B^{-}\to p\bar{p}{\ell }^{-}\bar{\hat{I}}{½}_{\ell })<9.6\times 10^{-6}$ at the 90% confidence level. This measurement helps constrain the baryonic transition form factor in B decays.

12 pages, 4 figures, submitted to Phys.Rev.Lett