First observation of ₁^0 c^ (*) ++ D^ (*) - K^- decays

The four decays, ₁^0 c^ (*) ++ D^ (*) - K^-, are observed for the first time using proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of 13\, TeV, corresponding to an integrated luminosity of 6\, fb^-1. By considering the b⁰ c^+ D⁰ K^- decay as reference channel, the following branching fraction ratios are measured to be B (₁^{0 ₂^++ D^- K^-) }B (₁^{0 c^+ D⁰ K^-) } = 0. 2820. 0160. 0160. 005, B (₁^{0 ₂^*++ D^- K^-) }B (₁^{0 c^++ D^- K^-) } = 0. 4600. 0520. 028, B (₁^{0 ₂^++ D^*- K^-) }B (₁^{0 c^++ D^- K^-) } = 2. 2610. 2020. 1290. 046, B (₁^{0 ₂^*++ D^*- K^-) }B (₁^{0 c^++ D^- K^-) } = 0. 8960. 1370. 0660. 018, where the first uncertainties are statistical, the second are systematic, and the third are due to uncertainties in the branching fractions of intermediate particle decays. These initial observations mark the beginning of pentaquark searches in these modes, with more data set to become available following the LHCb upgrade.