Observation of a narrow resonance of mass 2.46 GeV/c² decaying to D*_s⁺π⁰ and confirmation of the D*_sJ(2317) state

Using 13.5 fb^-1 of e⁺e^- annihilation data collected with the CLEO II detector, we have observed a narrow resonance decaying to D*_s⁺ π⁰ with a mass near 2.46 GeV/c². The search for such a state was motivated by the recent discovery by the BaBar Collaboration of a narrow state at 2.32 GeV/c ², the D*_sJ(2317)⁺, that decays to D _s⁺ π⁰. Reconstructing the D_s ⁺ π⁰ and D*_s⁺ π⁰ final states in CLEO data, we observe peaks in both of the corresponding reconstructed mass difference distributions, ΔM(D _sπ⁰) = M(D_sπ⁰) - M(D _s) and ΔM(D*_s π⁰) = M(D*_s π⁰) - M(D*_s), both of them at values near 350 MeV/c². We interpret these peaks as signatures of two distinct states, the D*_sJ(2317)⁺ plus a new state, designated as the D_sJ(2463)⁺. Because of the similar ΔM values, each of these states represents a source of background for the other if photons are lost, ignored or added. A quantitative accounting of these reflections confirms that both states exist. We have measured the mean mass differences 〈ΔM(D_s π⁰)〉 = 350.0 ±1.2 (stat) ± 1.0 (syst) MeV/c² for the D*_sJ(2317)⁺ state, and 〈ΔM(D* _s π⁰)〉 = 351.2 ± 1.7 (stat) ± 1.0 (syst) MeV/c² for the new D_sJ(2463)⁺ state. We have also searched, but find no evidence, for decays of the two states via the channels D*_s⁺ γ, D_s⁺ γ, and D_s⁺ π⁺ π^-. The observations of the two states at 2.32 and 2.46 GeV/c², in the D _s⁺ π⁰ and D*_s⁺ π⁰ decay channels, respectively, are consistent with their interpretations as cs̄ mesons with an orbital angular momentum L = 1 and spin and parity J^P = 0⁺ and 1⁺.