Investigation of the ΔI=1/2 Rule and Test of CP Symmetry through the Measurement of Decay Asymmetry Parameters in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" …

Using (10087±44)×106 J/ψ events collected with the BESIII detector, numerous Ξ− and Λ decay asymmetry parameters are simultaneously determined from the process J/ψ→Ξ−Ξ¯+→Λ(pπ−)π−Λ¯(n¯π0)π+ and its charge-conjugate channel. The precisions of αΛ0 for Λ→nπ0 and α¯Λ0 for Λ¯→n¯π0 compared to world averages are improved by factors of 4 and 1.7, respectively. The ratio of decay asymmetry parameters of Λ→nπ0 to that of Λ→pπ−, ⟨αΛ0⟩/⟨αΛ−⟩, is determined to be 0.873±0.012−0.010+0.011, where the first and the second uncertainties are statistical and systematic, respectively. The ratio is smaller than unity more than 5σ, which signifies the existence of the ΔI=3/2 transition in Λ for the first time. Besides, we test for CP symmetry in Ξ−→Λπ− and in Λ→nπ0 with the best precision to date. Published by the American Physical Society 2024