Using $980{\mathrm{fb}}^{-1}$ of data collected with the Belle detector operating at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider, we report a study of the electromagnetic decays of excited charmed baryons ${\mathrm{\Xi }}_c(2790)$ and ${\mathrm{\Xi }}_c(2815)$. A clear signal (8.6 standard deviations) is observed for ${\mathrm{\Xi }}_c(2815{)}^0\to {\mathrm{\Xi }}_c^0\gamma$, and we measure: $\frac{\mathcal{B}[{\mathrm{\Xi }}_c(2815{)}^0\to {\mathrm{\Xi }}_c^0\gamma ]}{\mathcal{B}[{\mathrm{\Xi }}_c(2815{)}^0\to {\mathrm{\Xi }}_c(2645{)}^{+}{\pi }^{-}\to {\mathrm{\Xi }}_c^0{\pi }^{+}{\pi }^{-}]}=0.41\pm 0.05\pm 0.03$. We also present evidence (3.8 standard deviations) for the similar decay of the ${\mathrm{\Xi }}_c(2790{)}^0$ and measure: $\frac{\mathcal{B}[{\mathrm{\Xi }}_c(2790{)}^0\to {\mathrm{\Xi }}_c^0\gamma ]}{\mathcal{B}[{\mathrm{\Xi }}_c(2790{)}^0\to {\mathrm{\Xi }}_c^{\prime +}{\pi }^{-}\to {\mathrm{\Xi }}_c^{+}\gamma {\pi }^{-}]}=0.13\pm 0.03\pm 0.02$. The first quoted uncertainties are statistical and the second systematic. We find no hint of the analogous decays of the ${\mathrm{\Xi }}_c(2815{)}^{+}$ and ${\mathrm{\Xi }}_c(2790{)}^{+}$ baryons and set upper limits at the 90% confidence level of: $\frac{\mathcal{B}[{\mathrm{\Xi }}_c(2815{)}^{+}\to {\mathrm{\Xi }}_c^{+}\gamma ]}{\mathcal{B}[{\mathrm{\Xi }}_c(2815{)}^{+}\to {\mathrm{\Xi }}_c(2645{)}^0{\pi }^{+}\to {\mathrm{\Xi }}_c^{+}{\pi }^{-}{\pi }^{+}]}<0.09$, and $\frac{\mathcal{B}[{\mathrm{\Xi }}_c(2790{)}^{+}\to {\mathrm{\Xi }}_c^{+}\gamma ]}{\mathcal{B}[{\mathrm{\Xi }}_c(2790{)}^{+}\to {\mathrm{\Xi }}_c^{\prime 0}{\pi }^{+}\to {\mathrm{\Xi }}_c^0\gamma {\pi }^{+}]}<0.06$. 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.

• Received 8 September 2020
• Accepted 30 September 2020

DOI:https://doi.org/10.1103/PhysRevD.102.071103

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Published by the American Physical Society