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Achasov, M. N.; Ahmed, S.; Amoroso, A.; An, F. F.; Bennett, J. V.; Bertani, M.; Chai, J.; Chen, H. S.; Cibinetto, G.; Cui, X. F.; Dai, H. L.; Fava, L.; Gao, Q.; Gao, Z.; Greco, M.; Hu, J. F.; Huesken, N.; Imoehl, W.; Irshad, M.; Jiang, X. S.; Kalantar-Nayestanaki, N.; Kavatsyuk, M.; Kiuchi, R.; Kolcu, O. B.; Kuessner, M.; Kühn, W.; Li, C.; Li, H. B.; Li, P. L.; Li, W. D.; Li, X. H.; Liang, Y. T.; Liao, G. R.; Liu, Huanhuan; Liu, K. Y.; Liu, X.; Liu, Y. B.; Luo, M. X.; Luo, T.; Lyu, X. R.; Ma, F. C.; Ma, L. L.; Maas, F. E.; Maldaner, S.; Mao, Y. J.; Meng, Z. X.; Min, T. J.; Mitchell, R. E.; Mo, Y. J.; Muchnoi, N. Yu; Nikolaev, I. B.; Niu, S. L.; Olsen, S. L.; Pacetti, S.; Pan, Y.; Patteri, P.; Peters, K.; Pitka, A.; Qi, M.; Qi, T. Y.; Rodin, V.; Shao, M.; Shen, P. X.; Sun, G. X.; Sun, Y. J.; Sun, Z. J.; Uman, I.; Wang, C. W.; Wang, D. Y.; Wang, H. H.; Wang, L. S.; Wang, M.; Wang, X.; Wang, X. F.; Wu, L. J.; Xu, L.; Xu, Q. J.; Xu, W.; Yang, Y. H.; Yang, Y. X.; Yang, Yifan; Ye, M.; You, Z. Y.; Yu, C. X.; Yuncu, A.; Zhang, B. Y.; Zhang, H. Y.; Zhang, J. Q.; Zhang, J. W.; Zhang, X. Y.; Zhang, Z. H.; Zhao, G.; Zhao, J. W.; Zhao, S. J.; Zheng, J. P.; Zhou, L.; Zhu, X. L.; Zhu, Y. C.; Zhuang, J.; Zou, B. S.
Physical review letters, 09/2019, Letnik: 123, Številka: 12Journal Article
The exclusive process e+e−→ΛΛ¯, with Λ→pπ− and Λ¯→p¯π+, has been studied at s=2.396 GeV for measurement of the timelike Λ electric and magnetic form factors, GE and GM. A data sample, corresponding to an integrated luminosity of 66.9 pb−1, was collected with the BESIII detector for this purpose. A multidimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio R=|GE/GM| and, for the first time for any baryon, the relative phase ΔΦ=ΦE−ΦM. The resulting values are R=0.96±0.14(stat)±0.02(syst) and ΔΦ=37°±12°(stat)±6°(syst), respectively. These are obtained using the recently established and most precise value of the asymmetry parameter αΛ=0.750±0.010 measured by BESIII. In addition, the cross section is measured with unprecedented precision to be σ=118.7±5.3(stat)±5.1(syst) pb, which corresponds to an effective form factor of |G|=0.123±0.003(stat)±0.003(syst). The contribution from two-photon exchange is found to be negligible. Our result enables the first complete determination of baryon timelike electromagnetic form factors.
