Observation of polarization in e+e- annihilation into a hyperon-antihyperon pair

by Dr Andrzej Kupsc (Uppsala University)

Thursday 10 May 2018, 10:00 → 11:00 Asia/Shanghai

B326 (IHEP)

Baryon-antibaryon pairs could be produced atelectron-positron colliders if sufficient center-of-mass energy is available. The process is strongly enhanced if the energy is tuned to match J/\psi or \psi' resonances. The spin orientations of the produced baryon and antibaryon are entangled and for the spin one-half baryons the system is described by just two complex parameters. If the relative phase is non-zero the produced particles are transversely polarized even if the beams are unpolarized. The polarization could be determined for hyperons from asymmetryof the decay distribution. A preliminary BESIII result shows that the phase for e^+ e^- \to J/\psi \to \Lambda \bar{\Lambda} is close to 45^{\circ}. The observed polarization and the spin correlations allow us to simultaneously measure decay parameters for \Lambda and \bar{\Lambda} hyperons. In particular we determine decay parameter \alpha_- for \Lambda \to p \pi^- for the first time since 1975. The value is more precise and (17 \pm 3)% larger than the world average. This has an important consequence for all experiments which rely on \Lambda \to p \pi^- for determination of the \Lambda polarization. Our result greatly enhances prospects for tests of CP violation and for determination of hyperon decay parameters at electron-positron colliders. About the speaker: Andrzej Kupsc, is a researcher working in the field experimental light hadron physics. He has obtained PhD at Soltan Institute for Nuclear Studies, Warsaw Poland in 1994 from an experiment at CELSIUS storage ring in Uppsala, Sweden. During postdoctoral fellowship at The Svedberg Laboratory, Uppsala he was responsible for WASA detector electromagnetic calorimeter assembly and tests at The Svedberg Laboratory in Uppsala. Since 1998 he has a permanent position at Uppsala University. Until recently his main research interests were production and decay studies of light neutral pseudoscalar mesons at WASA-at-COSY, KLOE-2 and BESIII experiments. More specifically most of his work has focused on meson transition form factors and dynamics of three body decays. This includes both analysis of the experimental data and the interpretation in collaboration with theory groups. He is physics coordinator for WASA-at-COSY and deputy physics coordinator for KLOE-2. During 2012-2014 he was spokesperson for MesonNet, a European Research Network, and now he is co-spokesperson of a proposal for EU research initiative “Precision Tests of the Standard Model” (PrecisionSM). The talk will be related to his recent research project concerning exclusive production of a hyperon-antihyperon pair in chamonia decays.

Slides Kupsc180510IHEP.pdf