First observation of the ${\overline{B}}_s^0\to {\Lambda }_c^{+}{\overline{\Lambda }}_c{}^{-}$ decay and evidence for the ${\overline{B}}^0\to {\Lambda }_c^{+}{\overline{\Lambda }}_c{}^{-}$ decay

Abstract

A search is presented for the two-body charmed baryonic decays ${\overline{B}}_{(s)}^0\to {\Lambda }_c^{+}{\overline{\Lambda }}_c{}^{-}$, using a data sample collected by the LHCb experiment during 2011--2012 and 2015--2018 corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. The first observation of the ${\overline{B}}_s^0\to {\Lambda }_c^{+}{\overline{\Lambda }}_c{}^{-}$ decay is reported with $6.2\sigma$ significance, along with $4.3\sigma$ evidence for the ${\overline{B}}^0\to {\Lambda }_c^{+}{\overline{\Lambda }}_c{}^{-}$ decay. The branching fractions are measured to be $\mathcal{B}({\overline{B}}^0\to {\Lambda }_c^{+}{\overline{\Lambda }}_c{}^{-})=(1.01_{-0.28}^{+0.27}\pm 0.08\pm 0.15)\times 10^{-5}$ and $\mathcal{B}({\overline{B}}_s^0\to {\Lambda }_c^{+}{\overline{\Lambda }}_c{}^{-})=(5.0\pm 1.3\pm 0.5\pm 0.8)\times 10^{-5}$, where the first uncertainty is statistical, the second systematic, and the third due to external inputs. These results provide novel experimental inputs for the theoretical framework describing two-body baryonic decays of $B$ mesons via $W$-emission and $W$-exchange mechanisms.

All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/1617/ (LHCb public pages)

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