Evidence for $B^{+}\to J/\psi p\overline{\Lambda }$ and Search for $B^0\to J/\psi p\overline{p}$

We have performed a search for the decays $B^{+}\to J/\psi p\overline{\Lambda }$ and $B^0\to J/\psi p\overline{p}$ in a data set of $(88.9\pm 1.0)\times {10}^6$ ${\rm Y}(4S)$ decays collected by the BABAR experiment at the PEP-II $e^{+}{e}^{-}$ storage ring at the Stanford Linear Accelerator Center. Four charged $B$ candidates have been observed with an expected background of $0.21\pm 0.14$ events. The corresponding branching fraction is $({12}_{-6}^{+9})\times {10}^{-6}$, where statistical and systematic uncertainties have been combined. The result can be interpreted as a 90% confidence level (C.L.) upper limit of $26\times {10}^{-6}$. We also find one $B^0$ candidate, with an expected background of $0.64\pm 0.17$ events, implying a 90% C.L. upper limit of $1.9\times {10}^{-6}$.

Figure 1

Center-of-mass momentum of $J/\psi$ mesons produced directly in $B$ decays (points) [2]. The histogram is the sum of the color-octet component from a recent NRQCD calculation [4] (dashed line), which includes multibody final states, and the color-singlet $J/\psi K^{(*)}$ component from simulation [5] (dotted line). Normalizations of the curves have been constrained to fit the data.

Figure 2

(a) Distribution of $B^{+}\to J/\psi p\overline{\Lambda }$ candidates in the $\Delta E$-$m_{\mathrm{E}\mathrm{S}}$ plane, with the signal ellipse and its projection in each dimension (dashed lines). Histogram of candidates within marked bands in (b) $m_{\mathrm{E}\mathrm{S}}$ and (c) $\Delta E$. Plots (d)–(f) Similar quantities for $B^0\to J/\psi p\overline{p}$.

Figure 3

Momentum in the $B^{+}$ rest frame of the (a) $J/\psi$, (b) proton, and (c) $\overline{\Lambda }$ daughters of the four $B^{+}\to J/\psi p\overline{\Lambda }$ candidates.