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

TL;DR

This study determines the spin and parity of the $\\Xi_{c}(2970)^+$ baryon using angular distribution analysis, establishing it as a $J^P=1/2^+$ state, which is the first such determination for a charmed-strange baryon.

Contribution

The paper provides the first experimental determination of the spin and parity of a charmed-strange baryon, specifically $\\Xi_{c}(2970)^+$, using decay angular distributions.

Findings

The $\\Xi_{c}(2970)^+$ has spin $J=1/2$.

The decay ratio $R$ supports $J^P=1/2^+$.

Angular distributions favor $J=1/2$ over higher spins.

Abstract

We report results from a study of the spin and parity of $\Xi_{c}(2970)^+$ using a $980~\mathrm{fb^{-1}}$ 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 $R={\mathcal{B}[ \Xi_{c}(2970)^+ \to \Xi_c(2645)^{0}\pi^{+} ]} / { \mathcal{B}[ \Xi_{c}(2970)^+ \to \Xi_c^{\prime0}\pi^{+} ]} =1.67 \pm 0.29\mathrm{(stat.)}^{ +0.15}_{ -0.09}\mathrm{(syst.)} \pm 0.25\mathrm{(IS)}$, 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.