Observation of excited $\hat{I}{\text{c◯}}_c^0$ baryons in $\hat{I}{\text{c◯}}_b^{-}\to \hat{I}{ž}_c^{+}{K}^{-}\ddot{I}{€}^{-}$ decays

Abstract

The first observation of the $\hat{I}{\text{c◯}}_b^{-}\to \hat{I}{ž}_c^{+}{K}^{-}\ddot{I}{€}^{-}$ decay is reported using $pp$ collision data at centre-of-mass energies of 7, 8 and 13\,$\mathrm{TeV}$ collected by the LHCb experiment, corresponding to an integrated luminosity of 9\,${\mathrm{fb}}^{-1}$. Four excited $\hat{I}{\text{c◯}}_c^0$ baryons are observed in the $\hat{I}{ž}_c^{+}{K}^{-}$ mass projection of the $\hat{I}{\text{c◯}}_b^{-}\to \hat{I}{ž}_c^{+}{K}^{-}\ddot{I}{€}^{-}$ decays with the significance of each exceeding five standard deviations. They coincide with the states previously observed in prompt \proton\proton and $e^{+}{e}^{-}$ production. Relative production rates, masses and natural widths of the states are measured, and a test of spin hypotheses is performed. Moreover, the branching ratio of $\hat{I}{\text{c◯}}_b^{-}\to \hat{I}{ž}_c^{+}{K}^{-}\ddot{I}{€}^{-}$ is measured relative to the $\hat{I}{\text{c◯}}_b^{-}\to \hat{I}{\text{c◯}}_c^0\ddot{I}{€}^{-}$ decay mode and a precise measurement of the $\hat{I}{\text{c◯}}_b^{-}$ mass of \mbox{$6044.3\pm 1.2\pm 1.1_{-0.22}^{+0.19}\mathrm{MeV}$} is obtained.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2021-012.html (LHCb public pages)