Observation of new ${\mathrm{\Xi }}_c^0$ baryons decaying to ${\mathrm{\Lambda }}_c^{+}{K}^{-}$

The ${\mathrm{\Lambda }}_c^{+}{K}^{-}$ mass spectrum is studied with a data sample of $pp$ collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6 fb${}^{-1}$ collected by the LHCb experiment. Three ${\mathrm{\Xi }}_c^0$ states are observed with a large significance and their masses and natural widths are measured to be \begin{eqnarray*} m(\Xi_c(2923)^0)&=& 2923.04 \pm 0.25 \pm 0.20 \pm 0.14 ~$\mathrm{M}\mathrm{e}\mathrm{V}$, \Gamma(\Xi_c(2923)^0) &=& 7.1 \pm 0.8 \pm 1.8 ~$\mathrm{M}\mathrm{e}\mathrm{V}$, \end{eqnarray*} \begin{eqnarray*} m(\Xi_c(2939)^0) &=& 2938.55 \pm 0.21 \pm 0.17 \pm 0.14 ~$\mathrm{M}\mathrm{e}\mathrm{V}$, \Gamma(\Xi_c(2939)^0) &=& 10.2 \pm 0.8 \pm 1.1 ~$\mathrm{M}\mathrm{e}\mathrm{V}$, \end{eqnarray*} \begin{eqnarray*} m(\Xi_c(2965)^0) &=& 2964.88 \pm 0.26 \pm 0.14 \pm 0.14~$\mathrm{M}\mathrm{e}\mathrm{V}$, \Gamma(\Xi_c(2965)^0) &=& 14.1 \pm 0.9 \pm 1.3~$\mathrm{M}\mathrm{e}\mathrm{V}$, \end{eqnarray*} where the uncertainties are statistical, systematic, and due to the limited knowledge of the ${\mathrm{\Lambda }}_c^{+}$ mass. The ${\mathrm{\Xi }}_c(2923{)}^0$ and ${\mathrm{\Xi }}_c(2939{)}^0$ baryons are new states. The ${\mathrm{\Xi }}_c(2965{)}^0$ state is in the vicinity of the known ${\mathrm{\Xi }}_c(2970{)}^0$ baryon; however, their masses and natural widths differ significantly.