A model-independent confirmation of the $Z(4430{)}^{-}$ state

The decay $B^0\to \psi (2S)K^{+}{\pi }^{-}$ is analyzed using $3\mathrm{f}{\mathrm{b}}^{-1}$ of $pp$ collision data collected with the LHCb detector. A model-independent description of the $\psi (2S)\pi$ mass spectrum is obtained, using as input the $K\pi$ mass spectrum and angular distribution derived directly from data, without requiring a theoretical description of resonance shapes or their interference. The hypothesis that the $\psi (2S)\pi$ mass spectrum can be described in terms of $K\pi$ reflections alone is rejected with more than 8$\sigma$ significance. This provides confirmation, in a model-independent way, of the need for an additional resonant component in the mass region of the $Z(4430{)}^{-}$ exotic state.