Study of Electromagnetic Decays of Orbitally Excited ${\Xi }_c$ Baryons

Abstract

Using 980 $f{b}^{-}1$ 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} ${\Xi }_c(2790)$ and ${\Xi }_c(2815)$. A clear signal (8.6 standard deviations) is observed for ${\Xi }_c(2815{)}^0\to {\Xi }_c^0\gamma$, and we measure: $B[{\Xi }_c(2815{)}^0\to {\Xi }_c^0\gamma ]/B[{\Xi }_c(2815{)}^0\to {\Xi }_c(2645{)}^{+}{\pi }^{-}\to {\Xi }_c^0{\pi }^{+}{\pi }^{-}]=0.41\pm 0.05\pm 0.03$. We also present evidence (3.8 standard deviations) for the similar decay of the ${\Xi }_c(2790{)}^0$ and measure: $B[{\Xi }_c(2790{)}^0\to {\Xi }_c^0\gamma ]/B[{\Xi }_c(2790{)}^0\to {\Xi }_c^{\prime +}{\pi }^{-}\to {\Xi }_c^{+}\gamma {\pi }^{-}]=0.13\pm 0.03\pm 0.02$. The first quoted uncertainties are statistical and the second systematic. We find no hint of the analogous decays of the ${\Xi }_c(2815{)}^{+}$ and ${\Xi }_c(2790{)}^{+}$ baryons and set upper limits at the 90% confidence level of: $B[{\Xi }_c(2815{)}^{+}\to {\Xi }_c^{+}\gamma ]/B[{\Xi }_c(2815{)}^{+}\to {\Xi }_c(2645{)}^0{\pi }^{+}\to {\Xi }_c^{+}{\pi }^{-}{\pi }^{+}]<0.09,$ and $B[{\Xi }_c(2790{)}^{+}\to {\Xi }_c^{+}\gamma ]/B[{\Xi }_c(2790{)}^{+}\to {\Xi }_c^{\prime 0}{\pi }^{+}\to {\Xi }_c^0\gamma {\pi }^{+}]<\mathrm{0.06.}$ 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.

Submitted to Phys. Rev. D (Rapid Communications)

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