Observation of a new excited $D_s^+$ meson in $B^0\to D^-D^+K^+π^-$ decays

Abstract: Using $pp$ collision data corresponding to an integrated luminosity of $5.4\,{\rm fb}<sup>{-1}$ collected with the LHCb detector at a center-of-mass energy of $13\,{\rm TeV}$, the $B^0\to D<sup>-D<sup>+K<sup>+\pi<sup>-$ decay is studied. A new excited $D_s<sup>+$ meson is observed decaying into the $D<sup>+K<sup>+\pi<sup>-$ 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 $m_R=2591\pm6\pm7\,{\rm MeV}$, $\Gamma_R=89\pm16\pm12\,{\rm MeV}$ and $J<sup>P=0<sup>-$, 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 $D_{s0}(2590)<sup>+$, is a strong candidate to be the $D_s(2<sup>1{S}_0)<sup>+$ state, the radial excitation of the pseudoscalar ground-state $D_s<sup>+$ meson.