München 2019 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 10: Hadron Structure and Spectroscopy II
HK 10.5: Talk
Monday, March 18, 2019, 17:45–18:00, HS 13
Proton Time-Like Electromagnetic Form Factor Measurement with the Scan Method at BESIII — •Christoph Rosner1, Yadi Wang1, Samer Ali Nasher Ahmed1, Alaa Dbeyssi1, Paul Larin1, Dexu Lin1, Frank Maas1,2,3, and Cristina Morales1 for the BESIII collaboration — 1Helmholtz-Institut Mainz, 55128 Mainz, Germany — 2Institute of Nuclear Physics, Mainz, Germany — 3PRISMA Cluster of Excellence, Mainz, Germany
Electromagnetic form factors (FF) provide valuable insight to the internal structure and dynamics of the proton. While they are well known in the space-like region through electron scattering experiments, the time-like region, typically accessed by annihilation experiments, is known with much less precision. Specifically the separation of the electric and magnetic FF has only been possible with low accuracy due to the low luminosity of previous data.
This contribution reports on the analysis based on 688.5 pb−1 of data taken at 22 energy points between 2.0 and 3.08 GeV with the Beijing Spectrometer III (BESIII) at the Beijing Electron Positron Collider II (BEPCII). The born cross section of e+e−→ pp is measured with the energy scan technique for the first time. Additionally, the absolute value of the proton electric and magnetic FF as well as their ratio are measured with high accuracy by analysing the helicity angular distribution of the outgoing protons.