Measurement of the spin of the Ξ(1530) resonance

Le résumé fourni par la source

The properties of the $\ensuremath{\Xi}(1530)$ resonance are investigated in the ${\ensuremath{\Lambda}}_{c}^{+}\ensuremath{\rightarrow}{\ensuremath{\Xi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{K}^{+}$ decay process. The data sample was collected with the BABAR detector at the SLAC PEP-II asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider operating at center-of-mass energies 10.58 and 10.54 GeV. The corresponding integrated luminosity is approximately $230\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. The spin of the $\ensuremath{\Xi}(1530)$ is established to be $3/2$. The existence of an $S$-wave amplitude in the ${\ensuremath{\Xi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ system is inferred, and its interference with the $\ensuremath{\Xi}(1530{)}^{0}$ amplitude provides the first clear demonstration of the Breit-Wigner phase motion expected for the $\ensuremath{\Xi}(1530)$. The ${P}_{1}(\mathrm{cos}{\ensuremath{\theta}}_{{\ensuremath{\Xi}}^{\ensuremath{-}}})$ Legendre polynomial moment indicates the presence of a significant $S$-wave amplitude for ${\ensuremath{\Xi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ mass values above $1.6\text{ }\text{ }\mathrm{GeV}/{c}^{2}$, and a dip in the mass distribution at approximately $1.7\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ is interpreted as due to the coherent addition of a $\ensuremath{\Xi}(1690{)}^{0}$ contribution to this amplitude. This would imply ${J}^{P}=1/{2}^{\ensuremath{-}}$ for the $\ensuremath{\Xi}(1690)$. Attempts at fitting the $\ensuremath{\Xi}(1530{)}^{0}$ line shape yield unsatisfactory results, and this failure is attributed to interference effects associated with the amplitudes describing the ${K}^{+}{\ensuremath{\pi}}^{+}$ and/or ${\ensuremath{\Xi}}^{\ensuremath{-}}{K}^{+}$ systems.

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