CP-violation studies of hyperon-antihyperon pairs with BESIII

Abstract

Two-body weak decays of polarized and entangled hyperon - antihyperon pairs, can be used for precision tests of the charge-parity (CP) symmetry. The BESIII experiment can produce these pairs via the two charmonium resonances, $J/\psi$ and $\psi(2S)$. Since two-body weak decays of hyperons are self-analyzing, both the spin polarization and the CP-odd decay parameters can be extracted from their decay distributions. The decay parameter values for the $\Lambda \to p \pi^-$, $\Sigma^+ \to p \pi^0$ and $\Xi \to \Lambda \pi^-$ and their corresponding charge conjugate decay modes have recently been determined by the BESIII collaboration. The decay parameter value for $\Lambda \to p \pi^-$ shows a significant difference from the consensus value. For the double weak decay, $\Xi\to\Lambda\pi^-\to p \pi^- \pi^-$, decay parameters can be obtained which are difficult to extract in single weak decays. By comparing the simultaneously obtained hyperon and antihyperon decay parameters tests of direct CP-violation can be performed which are complementary to the direct CP-violating measurements from $K\to \pi\pi$. In these proceedings, a short summary of the method and results are provided as well as an outlook of what can be expected from the BESIII collaboration in the near future.