Electromagnetic Form Factors of $\varLambda$ Hyperon in the Vector Meson Dominance Model and a Possible Explanation of the Near-Threshold Enhancement of the $e^+e^- \to \varLambda\bar{\varLambda}$ Reaction
Zhong-Yi Li1,2†, An-Xin Dai1,2†, and Ju-Jun Xie1,2,3,4*
1Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China 2School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 101408, China 3School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, China 4Lanzhou Center for Theoretical Physics, Key Laboratory of Theoretical Physics of Gansu Province, Lanzhou University, Lanzhou 730000, China
Abstract：The near-threshold $e^+e^- \to \varLambda\bar{\varLambda}$ reaction is studied with the assumption that the production mechanism is due to a near-$\varLambda \bar{\varLambda}$-threshold bound state. The cross section of the $e^+e^- \to \varLambda\bar{\varLambda}$ reaction is parameterized in terms of the electromagnetic form factors of $\varLambda$ hyperon, which are obtained with the vector meson dominance model. It is shown that the contribution to the $e^+e^- \to \varLambda\bar{\varLambda}$ reaction from a new narrow state with quantum numbers $J^{PC}=1^{--}$ 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 $\varLambda \bar{\varLambda}$, 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 $e^+e^- \to \varLambda\bar{\varLambda}$ reaction. We also note that the near-threshold enhancement can also be reproduced by including these well established vector resonances $\omega(1420)$, $\omega(1650)$, $\phi(1680)$, or $\phi(2170)$ with a Flatté form for their total decay width, and a strong coupling to the $\varLambda\bar{\varLambda}$ channel.
. [J]. 中国物理快报, 2022, 39(1): 11201-.
Zhong-Yi Li, An-Xin Dai, and Ju-Jun Xie. Electromagnetic Form Factors of $\varLambda$ Hyperon in the Vector Meson Dominance Model and a Possible Explanation of the Near-Threshold Enhancement of the $e^+e^- \to \varLambda\bar{\varLambda}$ Reaction. Chin. Phys. Lett., 2022, 39(1): 11201-.
2022, Vol. 39 
