The near-threshold e + e − → Λ Λ ¯ reaction is studied with the assumption that the production mechanism is due to a near- Λ Λ ¯ -threshold bound state. The cross section of the e + e − → Λ Λ ¯ reaction is parameterized in terms of the electromagnetic form factors of λ hyperon, which are obtained with the vector meson dominance model. It is shown that the contribution to the e + e − → Λ Λ ¯ reaction from a new narrow state with quantum numbers JPC = 1− is dominant for energies very close to threshold. The mass of this new state is around 2231 MeV, which is very close to the mass threshold of Λ Λ ¯ , while its width is just a few MeV. This gives a possible solution to the problem that all previous calculations seriously underestimated the near-threshold total cross section of the e + e − → Λ Λ ¯ reaction. We also note that the near-threshold enhancement can also be reproduced by including these well established vector resonances ω(1420), ω(1650), ϕ(1680), or ϕ(2170) with a Flatté form for their total decay width, and a strong coupling to the Λ Λ ¯ channel.

Based on the recently precise measurements of the electron-positron annihilation reactions into a neutron and anti-neutron pair by BESIII collaboration, the effective form factor of neutron was determined in the time like region, and it was found that the effective form factor of neutron is smaller than the ones of proton. The effective form factors of neutron shows a periodic behaviour, similar to the case of proton. Here, a compared analysis for $\Lambda$, $\Sigma^0$ and $\Xi^0$ is performed. Fits of the available data on the effective form factors of $\Lambda$, $\Sigma^0$ and $\Xi^0$ with charge zero, allow to show an interesting phenomenon of the oscillation behavior in their effective form factors. However, this needs to be confirmed by future precise experiments. Both theoretical and experimental investigations of this phenomenon can shed light on the reaction mechanisms of the electron-positron annihilation process. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.