The near-threshold e^(+)e^(-)→ΛΛ reaction is studied with the assumption that the production mechanism is due to a near-ΛΛ-threshold bound state. The cross section of the e^(+)e^(-)→ΛΛ reaction is parameterize...The near-threshold e^(+)e^(-)→ΛΛ reaction is studied with the assumption that the production mechanism is due to a near-ΛΛ-threshold bound state. The cross section of the e^(+)e^(-)→ΛΛ 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^(-)→ΛΛ reaction from a new narrow state with quantum numbersJ~(PC)= 1--is dominant for energies very close to threshold. The mass of this new state is around 2231 Me V,which is very close to the mass threshold of ΛΛ, while its width is just a few Me V. This gives a possible solution to the problem that all previous calculations seriously underestimated the near-threshold total cross section of the e^(+)e^(-)→ΛΛ 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 ΛΛ channel.展开更多
Based on the recent precise measurements by the BESIII collaboration for electron–positron annihilation into a neutron and antineutron pair,the effective form factors of the neutron were determined in the time-like r...Based on the recent precise measurements by the BESIII collaboration for electron–positron annihilation into a neutron and antineutron pair,the effective form factors of the neutron were determined in the time-like region,and it was found that the effective form factors of the neutron are smaller than those of the proton.The effective form factors of the neutron show a periodic behaviour,similar to those of the proton.Here,a comparative analysis forΛ,∑^(0)and■hyperons is performed.Fits of the available data on the effective form factors ofΛ,∑^(0)and■with zero charge show an interesting phenomenon in the oscillating behavior of their effective form factors.However,this will need 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 processes.展开更多
基金partly supported by the National Natural Science Foundation of China (Grant Nos. 12075288, 11735003, and 11961141012)supported by the Youth Innovation Promotion Association CAS。
文摘The near-threshold e^(+)e^(-)→ΛΛ reaction is studied with the assumption that the production mechanism is due to a near-ΛΛ-threshold bound state. The cross section of the e^(+)e^(-)→ΛΛ 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^(-)→ΛΛ reaction from a new narrow state with quantum numbersJ~(PC)= 1--is dominant for energies very close to threshold. The mass of this new state is around 2231 Me V,which is very close to the mass threshold of ΛΛ, while its width is just a few Me V. This gives a possible solution to the problem that all previous calculations seriously underestimated the near-threshold total cross section of the e^(+)e^(-)→ΛΛ 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 ΛΛ channel.
基金partly supported by the National Natural Science Foundation of China (12075288, 12135007, 11735003, 11961141012)partly supported by the Youth Innovation Promotion Association CAS
文摘Based on the recent precise measurements by the BESIII collaboration for electron–positron annihilation into a neutron and antineutron pair,the effective form factors of the neutron were determined in the time-like region,and it was found that the effective form factors of the neutron are smaller than those of the proton.The effective form factors of the neutron show a periodic behaviour,similar to those of the proton.Here,a comparative analysis forΛ,∑^(0)and■hyperons is performed.Fits of the available data on the effective form factors ofΛ,∑^(0)and■with zero charge show an interesting phenomenon in the oscillating behavior of their effective form factors.However,this will need 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 processes.
