Physicists Spot New Clues in the Universe's Biggest Symmetry Mystery
Scientists have made the first direct measurements of how certain particles decay in ways that could reveal why matter dominates over antimatter. Using data from the world's largest particle detector, researchers found no evidence of CP symmetry violations in these decays—a result that narrows where physicists should look next to solve one of physics' deepest unsolved problems.
Originaltitel: Strong and Weak <em>CP</em> Tests in Sequential Decays of Polarized Σ<sup>0</sup> Hyperons
<p>The J/psi,psi(3686) -> Sigma(0)(Sigma) over bar (0) processes and subsequent decays are studied using the world's largest J/psi and psi(3686) data samples collected with the BESIII detector. The parity-violating decay parameters of the decays Sigma(0) -> Lambda gamma and (Sigma) over bar (0) ->(Lambda) over bar gamma, alpha(Sigma 0) = -0.0017 +/- 0.0021 +/- 0.0018 and (alpha) over bar (Sigma 0) = 0.0021 +/- 0.0020 +/- 0.0022, are measured for the first time. The strong CP symmetry is tested in the decays of the S0 hyperons for the first time by measuring the asymmetry A(CP)(Sigma) = alpha(Sigma 0) + (alpha) over bar (Sigma 0) =(0.4 +/- 2.9 +/- 1.3) x 10(-3). The weak CP test is performed in the subsequent decays of their daughter particles Lambda and (Lambda) over bar. Also for the first time, the transverse polarizations of the Sigma(0) hyperons in J/psi and psi(3686) -> decays are observed with opposite directions, and the ratios between the S-wave and D-wave contributions of the J/psi, psi(3686) -> Sigma(0)(Sigma) over bar (0) decays are obtained. These results are crucial to understand the decay dynamics of the charmonium states and the production mechanism of the Sigma(0) - (Sigma) over bar (0) pairs.</p>