Ablikim, M.Achasov, M. N.Ahmed, S.Albrecht, M.Alekseev, M.Amoroso, A.Çetin, Serkant Ali2024-07-182024-07-1820191745-24731745-2481https://doi.org/10.1038/s41567-019-0494-8https://hdl.handle.net/11411/8925Particles directly produced at electron-positron colliders, such as the J/psi meson, decay with relatively high probability into a baryon-antibaryon pair(1). For spin-1/2 baryons, the pair can have the same or opposite helicites. A non-vanishing phase Delta Phi between the transition amplitudes to these helicity states results in a transverse polarization of the baryons(2-4). From the joint angular distribution of the decay products of the bary-ons, this phase as well as the parameters characterizing the baryon and the antibaryon decays can be determined. Here, we report the measurement of Delta Phi = 42.4 +/- 0.6 +/- 0.5 degrees using Lambda -> p pi(-) and (Lambda) over bar -> (p) over bar pi(+), (n ) over bar pi(0) decays at BESIII. We find a value for the Lambda -> p pi(-) decay parameter of alpha(-) = 0.750 +/- 0.009 +/- 0.004, 17 +/- 3% higher than the current world average, which has been used as input for all Lambda polarization measurements since 1978(5,6). For (Lambda) over bar -> (p) over bar pi(+) we find alpha(+) = -0.758 +/- 0.010 +/- 0.007, giving A(CP) = (alpha(-) + alpha(+))/(alpha(-) - alpha(+)) = -0.006 +/- 0.012 +/- 0.007, a precise direct test of charge-parity symmetry (CP) violation in Lambda decays.eninfo:eu-repo/semantics/openAccessAnalyzing PowerParameterJ/PsiDecayHyperonLambda(Lambda)Over-BarObservablesE(+)E(-)LambdaArticle2-s2.0-8506529577010.1038/s41567-019-0494-8+7Q163115Q1WOS:000473331000013