We report the first observation of the two-body baryonic decays B+ → Σc(2455)++ ̄Ξc− and B0 → Σc(2455)0 ̄Ξ0c with significances of 7.3σ and 6.2σ, respectively, including statistical and systematic uncertainties. The branching fractions are measured to be B(B+ → Σc(2455)++ ̄Ξ−c) =(5.74 ± 1.11 ± 0.42+2.47−1.53)× 10−4 and B(B0 → Σc(2455)0 ̄Ξ0c) = (4.83 ± 1.12 ± 0.37+0.72−0.60) × 10−4. The first and second uncertainties are statistical and systematic, respectively, while the third ones arise from the absolute branching fractions of ̄Ξ−c or ̄Ξ0c decays. The data samples used for this analysis have integrated luminosities of 711 fb−1 and 365 fb−1, and were collected at the Υ(4S) resonance by the Belle and Belle II detectors operating at the KEKB and SuperKEKB asymmetric-energy e+e− colliders, respectively.
