【摘 要】
：
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
【机 构】
：
Institute of Modern Physics,Chinese Academy of Sciences,Lanzhou 730000,China;School of Nuclear Scien
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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 w(1420),w(1650),φ(1680),or φ(2170) with a Flatté form for their total decay width,and a strong coupling to the Λ(Λ) channel.
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