Observation of new $\hat{I}{ž}_c^0$ baryons decaying to $\hat{I}{›}_c^{+}{K}^{-}$

Abstract

The $\hat{I}{›}_c^{+}{K}^{-}$ 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 $\hat{I}{ž}_c^0$ states are observed with a large significance and their masses and natural widths are measured to be \begin{eqnarray*} m(Ξ_c(2923)^0)&=& 2923.04 \pm 0.25 \pm 0.20 \pm 0.14 ~\mathrm{MeV}, Γ(Ξ_c(2923)^0) &=& 7.1 \pm 0.8 \pm 1.8 ~\mathrm{MeV}, \end{eqnarray*} \begin{eqnarray*} m(Ξ_c(2939)^0) &=& 2938.55 \pm 0.21 \pm 0.17 \pm 0.14 ~\mathrm{ MeV}, Γ(Ξ_c(2939)^0) &=& 10.2 \pm 0.8 \pm 1.1 ~\mathrm{ MeV}, \end{eqnarray*} \begin{eqnarray*} m(Ξ_c(2965)^0) &=& 2964.88 \pm 0.26 \pm 0.14 \pm 0.14~\mathrm{ MeV}, Γ(Ξ_c(2965)^0) &=& 14.1 \pm 0.9 \pm 1.3~\mathrm{ MeV}, \end{eqnarray*} where the uncertainties are statistical, systematic, and due to the limited knowledge of the $\hat{I}{›}_c^{+}$ mass. The $\hat{I}{ž}_c(2923{)}^0$ and $\hat{I}{ž}_c(2939{)}^0$ baryons are new states. The $\hat{I}{ž}_c(2965{)}^0$ state is in the vicinity of the known $\hat{I}{ž}_c(2970{)}^0$ baryon; however, their masses and natural widths differ significantly.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2020-004.html