Study of electromagnetic decays of orbitally excited Ξ c baryons

Le résumé fourni par la source

Using $980\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected with the Belle detector operating at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider, we report a study of the electromagnetic decays of excited charmed baryons ${\mathrm{\ensuremath{\Xi}}}_{c}(2790)$ and ${\mathrm{\ensuremath{\Xi}}}_{c}(2815)$. A clear signal (8.6 standard deviations) is observed for ${\mathrm{\ensuremath{\Xi}}}_{c}(2815{)}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}_{c}^{0}\ensuremath{\gamma}$, and we measure: $\frac{\mathcal{B}[{\mathrm{\ensuremath{\Xi}}}_{c}(2815{)}^{0}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}^{0}\ensuremath{\gamma}]}{\mathcal{B}[{\mathrm{\ensuremath{\Xi}}}_{c}(2815{)}^{0}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}(2645{)}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}^{0}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}]}=0.41\ifmmode\pm\else\textpm\fi{}0.05\ifmmode\pm\else\textpm\fi{}0.03$. We also present evidence (3.8 standard deviations) for the similar decay of the ${\mathrm{\ensuremath{\Xi}}}_{c}(2790{)}^{0}$ and measure: $\frac{\mathcal{B}[{\mathrm{\ensuremath{\Xi}}}_{c}(2790{)}^{0}\text{ }\ensuremath{\rightarrow}{\text{ }\mathrm{\ensuremath{\Xi}}}_{c}^{0}\ensuremath{\gamma}]}{\mathcal{B}[{\mathrm{\ensuremath{\Xi}}}_{c}(2790{)}^{0}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}^{\ensuremath{'}+}{\ensuremath{\pi}}^{\ensuremath{-}}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}^{+}\ensuremath{\gamma}{\ensuremath{\pi}}^{\ensuremath{-}}]}=0.13\ifmmode\pm\else\textpm\fi{}0.03\ifmmode\pm\else\textpm\fi{}0.02$. The first quoted uncertainties are statistical and the second systematic. We find no hint of the analogous decays of the ${\mathrm{\ensuremath{\Xi}}}_{c}(2815{)}^{+}$ and ${\mathrm{\ensuremath{\Xi}}}_{c}(2790{)}^{+}$ baryons and set upper limits at the 90% confidence level of: $\frac{\mathcal{B}[{\mathrm{\ensuremath{\Xi}}}_{c}(2815{)}^{+}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}^{+}\ensuremath{\gamma}]}{\mathcal{B}[{\mathrm{\ensuremath{\Xi}}}_{c}(2815{)}^{+}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}(2645{)}^{0}{\ensuremath{\pi}}^{+}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}]}<0.09$, and $\frac{\mathcal{B}[{\mathrm{\ensuremath{\Xi}}}_{c}(2790{)}^{+}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}^{+}\ensuremath{\gamma}]}{\mathcal{B}[{\mathrm{\ensuremath{\Xi}}}_{c}(2790{)}^{+}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}^{\ensuremath{'}0}{\ensuremath{\pi}}^{+}\text{ }\ensuremath{\rightarrow}\text{ }{\mathrm{\ensuremath{\Xi}}}_{c}^{0}\ensuremath{\gamma}{\ensuremath{\pi}}^{+}]}<0.06$. Approximate values of the partial widths of the decays are extracted, which can be used to discriminate between models of the underlying quark structure of these excited states.

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