Measurement of the decay asymmetry parameters in Ξc0→Ξ−π+

Using the CLEO II detector at the Cornell Electron Storage Ring we have measured the ${\ensuremath{\Xi}}_{c}^{0}$ decay asymmetry parameter in the decay ${\ensuremath{\Xi}}_{c}^{0}\ensuremath{\rightarrow}{\ensuremath{\Xi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}.$ We find ${\ensuremath{\alpha}}_{{\ensuremath{\Xi}}_{c}^{0}}{\ensuremath{\alpha}}_{\ensuremath{\Xi}}=0.26\ifmmode\pm\else\textpm\fi{}0.18{(\mathrm{stat})}_{\ensuremath{-}0.04}^{+0.05}(\mathrm{syst});$ using the world average value of ${\ensuremath{\alpha}}_{\ensuremath{\Xi}}=\ensuremath{-}0.456\ifmmode\pm\else\textpm\fi{}0.014$ we obtain ${\ensuremath{\alpha}}_{{\ensuremath{\Xi}}_{c}^{0}}=\ensuremath{-}0.56\ifmmode\pm\else\textpm\fi{}0.39{(\mathrm{stat})}_{\ensuremath{-}0.09}^{+0.10}(\mathrm{syst}).$ The physically allowed range of a decay asymmetry parameter is $\ensuremath{-}1<\ensuremath{\alpha}<+1.$ Our result prefers a negative value: ${\ensuremath{\alpha}}_{{\ensuremath{\Xi}}_{c}^{0}}$ is $<0.1$ at the 90% C.L. The central value occupies the middle of the theoretically expected range but is not yet precise enough to choose between models.