Bonn 2020 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 42: Hadron Structure and Spectroscopy VIII
HK 42.3: Talk
Thursday, April 2, 2020, 15:00–15:15, J-HS A
Surprising Features of the Neutron Electromagnetic Structure in Electron-Positron Annihilation — •Samer Ahmed1,2, Alaa Dbeyssi1, Paul Larin1,2, Frank Maas1,2,3, Christoph Rosner1,2, and Yadi Wang1 — 1Helmholtz-Institut Mainz, Mainz, Germany — 2Institute of Nuclear Physics, Mainz, Germany — 3PRISMA Cluster of Excellence, Mainz, Germany
The neutron is one of the building blocks of visible matter. Its complicated structure emerges from the binding of three quarks by strong interaction. It cannot be calculated from first principles due to the large color charge of quarks and due to the self-interaction of gluons. The electromagnetic form factors represent the simplest structure observables and serve as a test ground for our understanding of the strong interaction. The data situation for the neutron structure from annihilation processes is very scarce. In this contribution, we show new results for the cross section of the e+e− → nn process and the effective form factor of the neutron at 18 centre of mass energies in the range √s = (2.0 - 3.08) GeV using data sets being collected at the BESIII experiment with an integrated luminosity of 647.9 pb−1. The achieved accuracy of the results for the effective form factor of the neutron is of a similar level as those from the electron scattering data. The electric and the magnetic form factor of the neutron have been measured for the first time using data from the e+ e− annihilation. In this contribution, the results for the disentangled electric and magnetic form factor of the neutron will be shown as well.