Complete measurement of $Λ$ electromagnetic form factors
Creators: name: Ablikim, M.
name: Achasov, M. N.
name: Adlarson, P.
name: Ahmed, S.
name: Albrecht, M.
name: Alekseev, M.
name: Amoroso, A.
name: An, F. F.
name: An, Q.
name: Bai, Y.
name: Bakina, O.
name: Ferroli, R. Baldini
name: Ban, Y.
name: Begzsuren, K.
name: Bennett, J. V.
name: Berger, N.
name: Bertani, M.
name: Bettoni, D.
name: Bianchi, F.
name: Biernat, J.
name: Bloms, J.
name: Boyko, I.
name: Briere, R. A.
name: Cai, H.
name: Cai, X.
name: Calcaterra, A.
name: Cao, G. F.
name: Cao, N.
name: Cetin, S. A.
name: Chai, J.
name: Chang, J. F.
name: Chang, W. L.
name: Chelkov, G.
name: Chen, D. Y.
name: Chen, G.
name: Chen, H. S.
name: Chen, J. C.
name: Chen, M. L.
name: Chen, S. J.
name: Chen, Y. B.
name: Cheng, W.
name: Cibinetto, G.
name: Cossio, F.
name: Cui, X. F.
name: Dai, H. L.
name: Dai, J. P.
name: Dai, X. C.
name: Dbeyssi, A.
name: Dedovich, D.
name: Deng, Z. Y.
name: Denig, A.
name: Denysenko, I.
name: Destefanis, M.
name: De Mori, F.
name: Ding, Y.
name: Dong, C.
name: Dong, J.
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name: Dong, M. Y.
name: Dou, Z. L.
name: Du, S. X.
name: Fan, J. Z.
name: Fang, J.
name: Fang, S. S.
name: Fang, Y.
name: Farinelli, R.
name: Fava, L.
name: Feldbauer, F.
name: Felici, G.
name: Feng, C. Q.
name: Fritsch, M.
name: Fu, C. D.
name: Fu, Y.
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name: Gao, X. L.
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name: Gao, Y. G.
name: Gao, Z.
name: Garillon, B.
name: Garzia, I.
name: Gersabeck, E. M.
name: Gilman, A.
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name: Gong, L.
name: Gong, W. X.
name: Gradl, W.
name: Greco, M.
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name: Guo, L. B.
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name: Han, S.
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name: Heinsius, F. H.
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name: Huang, J. S.
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name: Liu, Huanhuan
name: Liu, Huihui
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name: Muramatsu, H.
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name: Nerling, F.
name: Nikolaev, I. B.
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name: Zhang, Y. T.
name: Zhang, Yang
name: Zhang, Yao
name: Zhang, Yi
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name: Zhou, Xiaoyu
name: Zhou, Xu
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name: Zhu, J.
name: Zhu, J.
name: Zhu, K.
name: Zhu, K. J.
name: Zhu, S. H.
name: Zhu, W. J.
name: Zhu, X. L.
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Publisher: name: arXiv
Year: 2019
Subjects: subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The exclusive process $e^+e^-\rightarrowΛ\barΛ$, with $Λ\to pπ^-$ and $\barΛ \to \bar{p}π^+$, has been studied at $\sqrt{s} =$ 2.396 GeV for measurement of the $Λ$ electric and magnetic form factors, $G_E$ and $G_M$. A data sample, corresponding to an integrated luminosity of 66.9 pb$^{-1}$, was collected with the BESIII detector for this purpose. A multi-dimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio $R=|G_E/G_M|$ and, for the first time for any baryon, the relative phase $ΔΦ=Φ_E-Φ_M$. The resulting values are obtained using the recent and most precise measured value of the asymmetry parameter $α_Λ$ = $0.750~\pm~0.010$ to be $R~=~0.96\pm0.14~(\rm stat.)\pm~0.02~(\rm sys.)$ and $ΔΦ=37^{\mathrm{o}}\pm~12^{\mathrm{o}}~(\rm stat.)\pm~6^{\mathrm{o}}~(\rm sys.)$, respectively. In addition, the cross section is measured with unprecedented precision to be $σ= 118.7~\pm~5.3~(\rm stat.)\pm~5.1~(\rm sys.)$ pb, which corresponds to an effective form factor of $|G|=0.123~\pm~0.003~(\rm stat.)\pm~0.003~(\rm sys.)$. The contribution from two-photon exchange is found to be negligible. Our result enables the first complete determination of baryon time-like electromagnetic form factors.
description: 7 pages, 3 figures, Submitted to Phys. Rev. Lett