Search for \bar{B}^0\toΛ_c^+\barΛ_c^- decay at Belle

Abstract

We search for the doubly charmed baryonic decay ${\bar{B}}^0\to {\Lambda }_c^{+}{\bar{\Lambda }}_c^{-}$, in a data sample of $520\times 10^6$ $B\bar{B}$ events accumulated at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric e^+e^- collider. We find no significant signal and set an upper limit of $\mathcal{B}({\bar{B}}^0\to {\Lambda }_c^{+}{\bar{\Lambda }}_c^{-})<6.2\times 10^{-5}$ at 90% confidence level. The result is significantly below a naive extrapolation from $\mathcal{B}(B^{-}\to {\Xi }_c^0{\bar{\Lambda }}_c^{)}$ assuming a simple Cabibbo-suppression factor of $|V_{cd}/V_{cs}{|}^2$. The small branching fraction could be attributed to a suppression due to the large momentum of the baryonic decay products, which has been observed in other charmed baryonic two-body B decays. trend observed in other charmed baryonic two-body B decays.

12 page, 5 figures. Contribution paper for conferences EPS2007 and Lepton Photon 2007, Belle-Conference-0707

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