Study of Decay Mechanisms in B−→Λc+p¯π− Decays and Observation of Low-Mass Structure in the Λc+p¯ System

Le résumé fourni par la source

Using a sample of $152\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ pairs accumulated with the Belle detector at the KEKB ${e}^{+}{e}^{\ensuremath{-}}$ collider, we study the decay mechanism of three-body charmed decay ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\Lambda}}_{c}^{+}\overline{p}{\ensuremath{\pi}}^{\ensuremath{-}}$. The intermediate two-body decay ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}_{c}(2455{)}^{0}\overline{p}$ is observed for the first time with a branching fraction of $(3.7\ifmmode\pm\else\textpm\fi{}0.7\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and a statistical significance of $8.4\ensuremath{\sigma}$. We also observe a low-mass enhancement in the $({\ensuremath{\Lambda}}_{c}^{+}\overline{p})$ system, which can be parametrized as a Breit-Wigner function with a mass of $({3.35}_{\ensuremath{-}0.02}^{+0.01}\ifmmode\pm\else\textpm\fi{}0.02)\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ and a width of $({0.07}_{\ensuremath{-}0.03}^{+0.04}\ifmmode\pm\else\textpm\fi{}0.04)\text{ }\text{ }\mathrm{GeV}/{c}^{2}$. We measure its branching fraction to be $({3.9}_{\ensuremath{-}0.7}^{+0.8}\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ with a statistical significance of $6.2\ensuremath{\sigma}$. The errors are statistical, systematic, and that of the ${\ensuremath{\Lambda}}_{c}^{+}\ensuremath{\rightarrow}p{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ decay branching fraction.

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