Seminarium Fizyki Wielkich Energii

Hyperon-antihyperon pairs from decays of vector charmonia are spin entangled. Furthermore, if the charmonia are produced in electron-positron collisions the hyperons can be polarized. Millions of the hyperon--antihyperon pairs events are available in the world's largest data of 10^10 J/psi and 2.7x10^9 psi(2S) collected at the BESIII experiment . The entangled pairs are used for precision determination of hyperon and antihyperon decay amplitudes and to test CP symmetry in the decays. The hyperon CP-symmetry tests are complementary to the direct CP-violation studies in kaon decays. I will present multi-dimensional analysis methods, developed by the Uppsala and Warsaw groups, that make use of the polarization and entanglement to achieve best sensitivity in the hyperon-decay measurements. Recent BESIII results obtained using these methods include studies of J/psi decays into Lambda-antiLambda and Xi- anti Xi+ published in Phys. Rev. Lett. and Nature, respectively. For the cascade decay chain, the exclusive measurement allows for three independent CP tests and determination of the strong and weak phase differences in the decay amplitudes.