HyperCP (E871) experiment at Fermilab: search for direct CP violation in hyperon decays

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The Fermilab HyperCP experiment has accumulated the world's largest sample of Ξ − and Ξ + hyperon decays within two running periods in 1997 and 1999. The primary goal of the experiment is to search for direct CP violation in the decay sequences Ξ − → Λ π − → p π − π − and Ξ + → Λ π + → p π + π +. A violation of CP would manifest itself as a difference between the angular distribution of the proton and the antiproton in the Λ and Λ helicity frame. The amount of data is enough to reach a statistical sensitivity of 1.4 × 10 −4 in the CP violating asymmetry A ΞΛ = (α Ξ α Λ − α Ξ α Λ )/(α Ξ α Λ + α Ξ α Λ ). We present an analysis method used to take into account the slight differences in the production of the Ξ − and Ξ + samples. A preliminary results on A ΞΛ at the level of a few 10 −3 and based on a few percent of the 1997 data will be presented.