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Complete Measurement of the Λ Electromagnetic Form Factors
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Nuclear Physics.ORCID iD: 0000-0001-6280-3851
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Nuclear Physics.
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Number of Authors: 4832019 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 12, article id 122003Article in journal (Refereed) Published
Abstract [en]

The exclusive process e(+)e(-) -> Lambda(Lambda) over bar, with Lambda -> p pi(-) and (Lambda) over bar -> (p) over bar pi(+), has been studied at root s = 2.396 GeV for measurement of the timelike Lambda 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 multidimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio R = vertical bar G(E)/G(M)vertical bar and, for the first time for any baryon, the relative phase Delta Phi = Phi(E) - Phi(M). The resulting values are R = 0.96 +/- 0.14(stat) +/- 0.02(syst) and Phi(F) = 37 degrees +/- 12 degrees (stat) +/- 6 degrees (syst), respectively. These are obtained using the recently established and most precise value of the asymmetry parameter alpha(Lambda) = 0.750 +/- 0.010 measured by BESIII. In addition, the cross section is measured with unprecedented precision to be sigma = 118.7 +/- 5.3(stat) +/- 5.1(syst) pb, which corresponds to an effective form factor of vertical bar G vertical bar = 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.

Place, publisher, year, edition, pages
2019. Vol. 123, no 12, article id 122003
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:uu:diva-395800DOI: 10.1103/PhysRevLett.123.122003ISI: 000487743500004OAI: oai:DiVA.org:uu-395800DiVA, id: diva2:1365556
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2016.0157
Note

For complete list of authors see http://dx.doi.org/10.1103/PhysRevLett.123.122003

Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-10-25Bibliographically approved

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Adlarson, PatrikBiernat, JacekIkegami Andersson, WalterJohansson, TordKupsc, AndrzejLi, CuiPapenbrock, MichaelPettersson, JoachimSchönning, KarinThorén, ViktorWolke, Magnus
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