Search for direct CP violation in Λ and Ξ hyperon decays

Abstract A sensitive search for direct CP violation in Ξ − ( Ξ + ) and Λ ( Λ ) decays is underway at FNAL. Experiment E871 (HyperCP) intends to perform a precision measurement of the angular distribution of protons (anti-protons) with respect to the helicity axis in the rest frame of the Λ ( Λ ). The slopes of these distributions give the decay parameters α Ξ α Λ and α Ξ α Λ . An asymmetry parameter A in terms of these decay parameters has been defined for which a non-zero value would be unambiguous evidence for direct CP violation. Theoretical predictions for A range from no asymmetry up to ∼ 10 −3 . HyperCP expects to measure A with an uncertainty of ∼ 2 × 10 −4 .