Speaker
Description
The lowest-mass charmonium ground state, the η_c(1S), serves as a crucial laboratory for testing quantum chromodynamics (QCD) and understanding charmonium decay dynamics. Utilizing its world-leading data samples of J/ψ and ψ(3686) events, the BESIII experiment has recently achieved significant progresses in the study of η_c decays. This presentation will report three key results. First, we will present the first observation of the $η_c → Ξ^0 Ξ̅^0$ decay, a hadronic decay mode involving a baryon-antibaryon pair. Second, we will report the first model-independent measurement of the absolute branching fraction of the $η_c → γγ$ decay, in which a sample of 0.16 million $η_c$ events are tagged via the channel $ψ(3686) → π^0 h_c, h_c → γη_c$ to avoid interference effects. Third, we will discuss a high-precision study of the magnetic dipole transition $J/ψ → γ η_c$, where the $η_c$ is reconstructed via its decay to $p \bar{p}$. It has significantly improved our knowledge of this key transition between charmonium S-wave states.
| Collaboration | BESIII |
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