Evidence for Semileptonic B- to p pbar l nubar Decays

TL;DR

This paper reports evidence for a rare semileptonic baryonic B decay, measuring its branching fraction and setting an upper limit, which provides insights into baryonic transition form factors in B decays.

Contribution

First evidence for the semileptonic decay B- to p pbar l nu using neural-network tagging and a large data sample, measuring its branching fraction and upper limit.

Findings

Branching fraction measured as (5.8^{+2.4}_{-2.1} (stat) ± 0.9 (syst))×10^{-6}

Significance of 3.2 sigma for the decay observation

Upper limit set at 9.6×10^{-6} at 90% confidence level

Abstract

We find evidence for the semileptonic baryonic decay $B^-\to p\bar p\ell^-\bar\nu_\ell$ ($\ell=e,\mu$), based on a data sample of 772 million $B\bar B$ pairs collected at the $\Upsilon(4S)$ 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 $B^-\to p\bar p\ell^-\bar\nu_\ell$ is measured to be $(5.8^{+2.4}_{-2.1}\textrm{(stat.)}\pm 0.9\textrm{(syst.)})\times 10^{-6}$ with a significance of 3.2$\sigma$, where lepton universality is assumed. We also estimate the corresponding upper limit: $\mathcal{B}(B^-\to p\bar p\ell^-\bar\nu_\ell) < 9.6\times 10^{-6}$ at the 90% confidence level. This measurement helps constrain the baryonic transition form factor in B decays.