Measurement of the decay asymmetry parameters in ${\Xi }_c^0\to {\Xi }^{-}{\pi }^{+}$

Using the CLEO II detector at the Cornell Electron Storage Ring we have measured the ${\Xi }_c^0$ decay asymmetry parameter in the decay ${\Xi }_c^0\to {\Xi }^{-}{\pi }^{+}.$ We find ${\alpha }_{{\Xi }_c^0}{\alpha }_{\Xi }=0.26\mathrm{}\pm 0.18{\mathrm{}\left(\mathrm{stat}\right)\mathrm{}}_{-0.04}^{+0.05\mathrm{}}\mathrm{}\left(\mathrm{syst}\right)\mathrm{};$ using the world average value of ${\alpha }_{\Xi }=-0.456\pm 0.014$ we obtain ${\alpha }_{{\Xi }_c^0}=-0.56\pm 0.39{\mathrm{}\left(\mathrm{stat}\right)\mathrm{}}_{-0.09}^{+0.10\mathrm{}}\mathrm{}\left(\mathrm{syst}\right)\mathrm{}.$ The physically allowed range of a decay asymmetry parameter is $-1<\mathrm{}\alpha <+1.\mathrm{}$ Our result prefers a negative value: ${\alpha }_{{\Xi }_c^0}$ is $<0.1\mathrm{}$ 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.