Investigation of the Δi=1/2 Rule and Test of CP Symmetry through the Measurement of Decay Asymmetry Parameters in Ξ- Decays

Usingo1008744 thorn x106J=psi events collected with the BESIII detector, numerous Xi-and Lambda decay asymmetry parameters are simultaneously determined from the processJ=psi ->Xi- Xi thorn ->Lambda op pi- thorn pi- Lambda o n pi 0 thorn pi thorn and its charge-conjugate channel. The precisions of alpha Lambda 0for Lambda -> n pi 0and alpha Lambda 0for Lambda -> n pi 0compared to world averages are improved by factors of 4 and 1.7, respectively. The ratio of decayasymmetry parameters of Lambda -> n pi 0to that of Lambda -> p pi-,h alpha Lambda 0i=h alpha Lambda-i, is determined to be0.8730.012 thorn 0.011-0.010, where the first and the second uncertainties are statistical and systematic, respectively.The ratio is smaller than unity more than5 sigma, which signifies the existence of the Delta I1/43=2transitionin Lambda for the first time. Besides, we test forCPsymmetry in Xi-->Lambda pi-and in Lambda -> n pi 0with the bestprecision to date