Observation of a new charged charmonium-like state in $\bar{B}^{0} -> J/\psi K^{-}\pi^{+}$ decays

We present the results of an amplitude analysis of ${\overline{B}}^{0}\to J/\psi {K}^{-}{\pi }^{+}$ decays. A new charged charmoniumlike state ${Z}_{c}\left(4200{\right)}^{+}$ decaying to $J/\psi {\pi }^{+}$ is observed with a significance of $6.2\sigma $. The mass and width of the ${Z}_{c}\left(4200{\right)}^{+}$ are $419{6}_{-29-13}^{+31+17}\text{}\text{}\mathrm{MeV}/{c}^{2}$ and $37{0}_{-70-132}^{+70+70}\text{}\text{}\mathrm{MeV}$, respectively; the preferred assignment of the quantum numbers is ${J}^{P}={1}^{+}$. In addition, we find evidence for ${Z}_{c}\left(4430{\right)}^{+}\to \phantom{\rule{0ex}{0ex}}J/\psi {\pi }^{+}$. The analysis is based on a $711\text{}\text{}{\mathrm{fb}}^{-1}$ data sample collected by the Belle detector at the asymmetric-energy ${e}^{+}{e}^{-}$ collider KEKB.