Complete Measurement of the Λ Electromagnetic Form Factors

(BESIII Collaboration)

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

The exclusive process e+e-→ΛΛ̄, with Λ→pπ- and Λ̄→p̄π+, 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.

Original languageEnglish (US)
Article number122003
JournalPhysical Review Letters
Volume123
Issue number12
DOIs
StatePublished - Sep 20 2019

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form factors
electromagnetism
baryons
luminosity
asymmetry
decomposition
detectors
cross sections
photons

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Complete Measurement of the Λ Electromagnetic Form Factors. / (BESIII Collaboration).

In: Physical Review Letters, Vol. 123, No. 12, 122003, 20.09.2019.

Research output: Contribution to journalArticle

(BESIII Collaboration). / Complete Measurement of the Λ Electromagnetic Form Factors. In: Physical Review Letters. 2019 ; Vol. 123, No. 12.
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abstract = "The exclusive process e+e-→ΛΛ̄, with Λ→pπ- and Λ̄→p̄π+, 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.",
author = "{(BESIII Collaboration)} and M. Ablikim and Achasov, {M. N.} and P. Adlarson and S. Ahmed and M. Albrecht and M. Alekseev and A. Amoroso and An, {F. F.} and Q. An and Y. Bai and O. Bakina and {Baldini Ferroli}, R. and Y. Ban and K. Begzsuren and Bennett, {J. V.} and N. Berger and M. Bertani and D. Bettoni and F. Bianchi and J. Biernat and J. Bloms and I. Boyko and Briere, {R. A.} and H. Cai and X. Cai and A. Calcaterra and Cao, {G. F.} and N. Cao and Cetin, {S. A.} and J. Chai and Chang, {J. F.} and Chang, {W. L.} and G. Chelkov and Chen, {D. Y.} and G. Chen and Chen, {H. S.} and Chen, {J. C.} and Chen, {M. L.} and Chen, {S. J.} and Chen, {Y. B.} and W. Cheng and G. Cibinetto and F. Cossio and Cui, {X. F.} and Dai, {H. L.} and Dai, {J. P.} and Dai, {X. C.} and A. Dbeyssi and D. Dedovich and Deng, {Z. Y.}",
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AU - Bertani, M.

AU - Bettoni, D.

AU - Bianchi, F.

AU - Biernat, J.

AU - Bloms, J.

AU - Boyko, I.

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AU - Chen, S. J.

AU - Chen, Y. B.

AU - Cheng, W.

AU - Cibinetto, G.

AU - Cossio, F.

AU - Cui, X. F.

AU - Dai, H. L.

AU - Dai, J. P.

AU - Dai, X. C.

AU - Dbeyssi, A.

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