Search for Direct CP Violation in $Ξ$ Hyperon Decay

Abstract

Using data collected with the CLEO II detector we have performed a search for direct CP violation in the $Ξ$ hyperon system. CP violation gives rise to an asymmetry, A, between the parity-violating angular distributions of the decay chains $Ξ^- \To Λpi^-$, $Λ\To p π^-$ and $\barΞ^+ \To \barΛ π^+$, $\barΛ \To \bar{p} π^+$. In the Standard Model, A is expected to be in the range $10^{-4}$ to $10^{-5}$. If CP violation were found at a higher level it could indicate the presence of new physics. We find no evidence for CP violation: A = -0.057 +- 0.064 +- 0.039. We also obtain $A_Ξ = -0.070 +- 0.064 +- 0.045$ and $α_{\barΞ}= 0.49^{+0.06}_{-0.05} +- 0.10$.