Observation of the Open-Charm Tetraquark Candidate Tcs0*(2870)0 in the B−→D−D0KS0 Decay

An amplitude analysis of B− → D−D0K0 S decays is performed using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1, collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. A resonant structure of spin-parity 0þ is observed in the D0K0 S invariant-mass spectrum with a significance of 5.3σ. The mass and width of the state, modeled with a Breit-Wigner line shape, are determined to be 2883 11 8 MeV=c2 and 87þ22 −47 17 MeV, 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 T cs0ð2870Þ0 observed previously in the DþK− final state of the B− → D−DþK− decay. This result confirms the existence of the T cs0ð2870Þ0 state in a new decay mode. The T cs1ð2900Þ0 state, reported in the B− → D−DþK− decay, is also searched for in the D0K0 S invariant-mass spectrum of the B− → D−D0K0 S decay, without finding evidence for it.