Szczegóły publikacji

A search is presented for the two-body charmed baryonic decays, $\bar{B}_{(s)}^0 \to \Lambda_c^+ \bar{\Lambda}_c^-$, 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 $\bar{B}_s^0 \to \Lambda_c^+ \bar{\Lambda}_c^-$ decay is reported with $6.2\sigma$ significance along with $4.3\sigma$ evidence for the $\bar{B}^0 \to \Lambda_c^+ \bar{\Lambda}_c^-$ decay. The branching fractions are measured to be \[ \mathcal{B}(\bar{B}^0 \to \Lambda_c^+ \bar{\Lambda}_c^-) = \left(1.01^{+0.27}_{-0.28} \pm 0.08 \pm 0.15 \right)\times 10^{-5} \] and \[ \mathcal{B}(\bar{B}_s^0 \to \Lambda_c^+ \bar{\Lambda}_c^-) = \left(5.0 \pm 1.3 \pm 0.5 \pm 0.8 \right)\times 10^{-5}, \] 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.