Searches for the baryon- and lepton-number violating decays $B^0\to {\Lambda }_c^{+}{l}^{-}$, $B^{-}\to \Lambda l^{-}$, and $B^{-}\to \overline{\Lambda }{l}^{-}$

Searches for $B$ mesons decaying to final states containing a baryon and a lepton are performed, where the baryon is either ${\Lambda }_c$ or $\Lambda$ and the lepton is a muon or an electron. These decays violate both baryon and lepton number and would be a signature of physics beyond the standard model. No significant signal is observed in any of the decay modes, and upper limits in the range $(3.2–520)\times {10}^{-8}$ are set on the branching fractions at the 90% confidence level.

Figure 1

Data for all events in the fitting region with overlaid fit results for $B^0\to {\Lambda }_c^{+}{\ell }^{-}$ candidates. The left column is for the muon mode and the right column the electron mode. Distributions of (a), (b) $m_{\mathrm{ES}}$; (c), (d) $\Delta E$, and (e), (f) neural net (NN) output are shown. Dashed lines represent the background components of the fit and solid lines represent the sum of the signal and background components. The lack of a significant signal makes the solid and dashed lines indistinguishable in some plots. In panels (e) and (f), the vertical dashed line indicates the selection criteria on the neural net output.

Figure 2

Data for all events in the fitting region with overlaid fit results for $B^{-}\to \Lambda {\ell }^{-}$ candidates. The left column is for the muon mode and the right column the electron mode. Distributions of (a), (b) $m_{\mathrm{ES}}$ and (c), (d) $\Delta E$ are shown. Dashed lines represent the background components of the fit and solid lines represent the sum of the signal and background components. The lack of a significant signal makes the solid and dashed lines indistinguishable in some plots.

Figure 3

Data for all events in the fitting region with overlaid fit results for $B^{-}\to \overline{\Lambda }{\ell }^{-}$ candidates. The left column is for the muon mode and the right column the electron mode. Distributions of (a), (b) $m_{\mathrm{ES}}$ and (c), (d) $\Delta E$ are shown. Dashed lines represent the background components of the fit and solid lines represent the sum of the signal and background components. The lack of a significant signal makes the solid and dashed lines indistinguishable in some plots.