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

Abstract

We report results from a study of the spin and parity of $\hat{I}{ž}_c(2970{)}^{+}$ 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 $\hat{I}{ž}_c(2970{)}^{+}\to \hat{I}{ž}_c(2645{)}^0\ddot{I}{€}^{+}\to \hat{I}{ž}_c^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}$ are analyzed to determine the spin of this charmed-strange baryon. The angular distributions strongly favor the $\hat{I}{ž}_c(2970{)}^{+}$ 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 $\hat{I}{ž}_c(2970{)}^{+}$ decay branching fractions $R=\mathcal{B}[\hat{I}{ž}_c(2970{)}^{+}\to \hat{I}{ž}_c(2645{)}^0\ddot{I}{€}^{+}]/\mathcal{B}[\hat{I}{ž}_c(2970{)}^{+}\to \hat{I}{ž}_c^{\prime 0}\ddot{I}{€}^{+}]=1.67\pm 0.29{(stat.)}_{-0.09}^{+0.15}(syst.)\pm 0.25(\mathrm{IS})$, 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