Observation of the Open-Charm Tetraquark Candidate 𝑇^∗_e⁢𝑠⁢0⁢(2870)⁰ in the 𝐵‾→𝐷‾𝐷⁰𝐾_s⁰ Decay

An amplitude analysis of (Formula presented) decays is performed using proton-proton collision data, corresponding to an integrated luminosity of (Formula presented), collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. A resonant structure of spin-parity (Formula presented) is observed in the (Formula presented) invariant-mass spectrum with a significance of (Formula presented). The mass and width of the state, modeled with a Breit-Wigner line shape, are determined to be (Formula presented) and (Formula presented), respectively, where the first uncertainties are statistical and the second systematic. These properties and the quark content are consistent with those of the open-charm tetraquark candidate (Formula presented) observed previously in the (Formula presented) final state of the (Formula presented) decay. This result confirms the existence of the (Formula presented) state in a new decay mode. The (Formula presented) state, reported in the (Formula presented) decay, is also searched for in the (Formula presented) invariant-mass spectrum of the (Formula presented) decay, without finding evidence for it.