Study of the B−→Λc+Λ¯c−K− decay

Résumé fourni par la source

The decay ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{\overline{\mathrm{\ensuremath{\Lambda}}}}_{c}^{\ensuremath{-}}{K}^{\ensuremath{-}}$ is studied in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13\text{ }\text{ }\mathrm{TeV}$ using data corresponding to an integrated luminosity of $5\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ collected by the LHCb experiment. In the ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{K}^{\ensuremath{-}}$ system, the ${\mathrm{\ensuremath{\Xi}}}_{c}(2930{)}^{0}$ state observed at the BABAR and Belle experiments is resolved into two narrower states, ${\mathrm{\ensuremath{\Xi}}}_{c}(2923{)}^{0}$ and ${\mathrm{\ensuremath{\Xi}}}_{c}(2939{)}^{0}$, whose masses and widths are measured to be $m({\mathrm{\ensuremath{\Xi}}}_{c}(2923{)}^{0})=2924.5\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\pm\else\textpm\fi{}1.1\text{ }\text{ }\mathrm{MeV}$, $m({\mathrm{\ensuremath{\Xi}}}_{c}(2939{)}^{0})=2938.5\ifmmode\pm\else\textpm\fi{}0.9\ifmmode\pm\else\textpm\fi{}2.3\text{ }\text{ }\mathrm{MeV}$, $\mathrm{\ensuremath{\Gamma}}({\mathrm{\ensuremath{\Xi}}}_{c}(2923{)}^{0})=\phantom{\rule{0ex}{0ex}}4.8\ifmmode\pm\else\textpm\fi{}0.9\ifmmode\pm\else\textpm\fi{}1.5\text{ }\text{ }\mathrm{MeV}$, $\mathrm{\ensuremath{\Gamma}}({\mathrm{\ensuremath{\Xi}}}_{c}(2939{)}^{0})=11.0\ifmmode\pm\else\textpm\fi{}1.9\ifmmode\pm\else\textpm\fi{}7.5\text{ }\text{ }\mathrm{MeV}$, where the first uncertainties are statistical and the second systematic. The results are consistent with a previous LHCb measurement using a prompt ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{K}^{\ensuremath{-}}$ sample. Evidence of a new ${\mathrm{\ensuremath{\Xi}}}_{c}(2880{)}^{0}$ state is found with a local significance of $3.8\ensuremath{\sigma}$, whose mass and width are measured to be $2881.8\ifmmode\pm\else\textpm\fi{}3.1\ifmmode\pm\else\textpm\fi{}8.5\text{ }\text{ }\mathrm{MeV}$ and $12.4\ifmmode\pm\else\textpm\fi{}5.3\ifmmode\pm\else\textpm\fi{}5.8\text{ }\text{ }\mathrm{MeV}$, respectively. In addition, evidence of a new decay mode ${\mathrm{\ensuremath{\Xi}}}_{c}(2790{)}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{K}^{\ensuremath{-}}$ is found with a significance of $3.7\ensuremath{\sigma}$. The relative branching fraction of ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{\overline{\mathrm{\ensuremath{\Lambda}}}}_{c}^{\ensuremath{-}}{K}^{\ensuremath{-}}$ with respect to the ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{D}^{+}{D}^{\ensuremath{-}}{K}^{\ensuremath{-}}$ decay is measured to be $2.36\ifmmode\pm\else\textpm\fi{}0.11\ifmmode\pm\else\textpm\fi{}0.22\ifmmode\pm\else\textpm\fi{}0.25$, where the first uncertainty is statistical, the second systematic and the third originates from the branching fractions of charm hadron decays.

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