First Determination of the Spin and Parity of a Charmed-Strange Baryon, ${\Xi }_c(2970{)}^{+}$

Abstract

We report results from a study of the spin and parity of ${\Xi }_c(2970{)}^{+}$ using a $980\mathrm{f}{\mathrm{b}}^{-1}$ data sample collected by the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The decay angle distributions in the chain ${\Xi }_c(2970{)}^{+}\to {\Xi }_c(2645{)}^0{\pi }^{+}\to {\Xi }_c^{+}{\pi }^{-}{\pi }^{+}$ are analyzed to determine the spin of this charmed-strange baryon. The angular distributions strongly favor the ${\Xi }_c(2970{)}^{+}$ spin $J=1/2$ over $3/2$ or $5/2$, under an assumption that the lowest partial wave dominates in the decay. We also measure the ratio of ${\Xi }_c(2970{)}^{+}$ decay branching fractions $R=\mathcal{B}[{\Xi }_c(2970{)}^{+}\to {\Xi }_c(2645{)}^0{\pi }^{+}]/\mathcal{B}[{\Xi }_c(2970{)}^{+}\to {\Xi }_c^{\prime 0}{\pi }^{+}]=1.67\pm 0.29{(stat.)}_{-0.09}^{+0.15}(syst.)\pm 0.25(\mathrm{IS})$, where the last uncertainty is due to possible isospin-symmetry-breaking effects. This $R$ value favors the spin-parity $J^P=1/2^{+}$ with the spin of the light-quark degrees of freedom $s_l=0$. This is the first determination of the spin and parity of a charmed-strange baryon.

To be submitted to Physical Review Letters

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