Spectroscopy of Strange Mesons and First Observation of a Strange Crypto-Exotic State with $J^P=0^{-}$

We measured the strange-meson spectrum in the scattering reaction $K^{-}+p\to K^{-}{\pi }^{-}{\pi }^{-}+p$ with the COMPASS spectrometer at CERN. Using the world’s largest sample of this reaction, we performed a comprehensive partial-wave analysis of the mesonic final state. It substantially extends the strange-meson spectrum covering twelve states with masses up to 2.4 GeV/$c^2$. We observe the first candidate for a crypto-exotic strange meson with $J^P=0^{-}$ and find $K_3$ and $K_4$ states consistent with predictions for the ground states.