Study of the rare hyperon decay

We report a new measurement of the decay Ω − → Ξ − π + π − with 76 events and a first observation of the decay Ω ¯ + → Ξ ¯ + π + π − with 24 events, yielding a combined branching ratio ( 3.74 − 0.56 + 0.67 ) × 10 − 4 . This represents a factor 25 increase in statistics over the best previous measurement. No evidence is seen for CP violation, with B ( Ω − → Ξ − π + π − ) = 4.04 − 0.71 + 0.83 × 10 − 4 and B ( Ω ¯ + → Ξ ¯ + π + π − ) = 3.15 − 0.89 + 1.12 × 10 − 4 . Contrary to theoretical expectation, we see little evidence for the decays Ω − → Ξ 1530 ∗ 0 π − and Ω ¯ + → Ξ ¯ 1530 ∗ 0 π + and place a 90% C.L. upper limit on the combined branching ratio B ( Ω − ( Ω ¯ + ) → Ξ 1530 ∗ 0 ( Ξ ¯ 1530 ∗ 0 ) π ∓ ) 7.0 × 10 − 5 .