Observation of a New Excited 𝐷+𝑠 Meson in 𝐵0→𝐷−⁢𝐷+⁢𝐾+⁢𝜋− Decays

Using 𝑝⁢𝑝 collision data corresponding to an integrated luminosity of 5.4  fb−1 collected with the LHCb detector at a center-of-mass energy of 13 TeV, the 𝐵0→𝐷−⁢𝐷+⁢𝐾+⁢𝜋− decay is studied. A new excited 𝐷+𝑠 meson is observed decaying into the 𝐷+⁢𝐾+⁢𝜋− final state with large statistical significance. The pole mass and width, and the spin parity of the new state are measured with an amplitude analysis to be 𝑚𝑅=2591±6±7  MeV, Γ𝑅=89±16±12  MeV, and 𝐽𝑃=0−, where the first uncertainty is statistical and the second systematic. Fit fractions for all components in the amplitude analysis are also reported. The new resonance, denoted as 𝐷𝑠⁢0⁢(2590)+, is a strong candidate to be the 𝐷𝑠⁢(2⁢1𝑆0)+ state, the radial excitation of the pseudoscalar ground-state 𝐷+
𝑠 meson.