Abstract
Hyperons are a powerful diagnostic tool that can shed light on some of the most intriguing questions in contemporary physics. Electromagnetic form factors (EMFFs) are currently the best way to study hyperon structure. In the time-like region the EMFFs can be complex with a relative phase. A non-zero phase polarizes the final state even when the initial state is unpolarized. A dedicated data sample collected by the BESIII experiment allowed for a first complete reconstruction of Λ in the time-like region. The ratio, R and relative phase between the electric and magnetic form factor, ΔΦ are measured to be 0.96±0.14(stat)±0.002(syst) and 37°±12°(stat)±6°(syst), respectively. In addition, the BESIII experiment has collected the world’s largest J/ψ data sample. Due to symmetric excellent detector conditions and low hadronic background, the experiment offers a clean environment for CP-violation tests using . That hyperons can be polarized allows for a simultaneous measurement of angular distributions of hyperons and antihyperons and to test CP symmetry directly. This has been done for the process recently measured by the BESIII experiment. The experimental results showed that the asymmetry decay parameter α(Λ → ππ−) = +0.750±0.009±0.004, is nearly twenty percent larger compared to the old PDG tabulated value. The test on CP symmetry, is the most sensitive test for Λ CP-violation. Preliminary results are presented for the process . The asymmetry decay parameter and −0.015 ± 0.037 ± 0.008 are both measured for the first time.
Highlights
The fundamental objective of hadron physics is to understand the structure of matter at the femtometer scale
In the time-like region the Electromagnetic form factors (EMFFs) can be complex with a relative phase
The experimental results showed that the asymmetry decay parameter α(Λ → pπ−) = +0.750 ± 0.009 ± 0.004, is nearly twenty percent larger compared to the old PDG tabulated value
Summary
The fundamental objective of hadron physics is to understand the structure of matter at the femtometer scale. Hyperons consist of one or more strange quarks and there exist relatively few form factors measurements. One can study both the space- and time-like region of hyperon EMFFs. The two regions can be related to each other via dispersion relations [4]. To study hyperon EMFFs in the time-like region a dedicated data sample has been collected by the BESIII experiment [22]. The BESIII experiment has collected 1010 J/ψ This is the world’s largest data sample produced directly from electron-positron annihilation, and allows for several stringent precision tests on CP symmetry
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