Measurement of masses of the ${\mathrm{\Xi }}_c(2645)$ and ${\mathrm{\Xi }}_c(2815)$ baryons and observation of ${\mathrm{\Xi }}_c(2980)\to {\mathrm{\Xi }}_c(2645)\pi$ %and observation of the ${\mathrm{\Xi }}_c(2980)$ and observation of ${\mathrm{\Xi }}_c(2980)\to {\mathrm{\Xi }}_c(2645)\pi$

We report a precise measurement of the masses of the ${\mathrm{\Xi }}_c(2645)$ and ${\mathrm{\Xi }}_c(2815)$ baryons using a data sample of 414 fb${}^{-1}$ collected by the Belle collaboration at the KEKB $e^{+}{e}^{-}$ collider. The states ${\mathrm{\Xi }}_c(2645{)}^{0,+}$ are observed in the ${\mathrm{\Xi }}_c^{+,0}{\pi }^{-,+}$ decay modes, while the ${\mathrm{\Xi }}_c(2815{)}^{0,+}$ are reconstructed in the ${\mathrm{\Xi }}_c(2645{)}^{+,0}{\pi }^{-,+}$ decay modes. The following mass splittings are determined: $m_{\Xi_c(2645)^+} - m_{\Xi_c(2645)^0} = (-0.1 \pm 0.3 ({\rm stat}) \pm 0.6 {(\rm syst})) {\rm MeV}/{\rm c}^2$and$m_{\Xi_c(2815)^+} - m_{\Xi_c(2815)^0} = (-3.4 \pm 1.9 ({\rm stat}) \pm 0.9 {(\rm syst})) {\rm MeV}/{\rm c}^2$ with a much better precision than the current world averages. We also observe a new decay mode, $\Xi_c(2980)^{0,+} \to \Xi_c(2645)^{+,0}\pi^{-,+}$.