Abstract
Electromagnetic form factors are fundamental quantities which parameterize the electric and magnetic structure of hadrons. This contribution reports on the measurements of baryon electromagnetic form factors at the BESIII experiment in Beijing. The Beijing e + e − collider BEPCII is a double-ring symmetric collider running at √s between 2.0 and 4.6 GeV. Baryon electromagnetic form factors can be measured at BESIII in direct e + e − -annihilation and in initial state radiation processes. Based on the data collected by the BESIII detector at 12 center of mass energies between 2.23 and 3.67 GeV, the e + e − → pp cross section and the time-like proton form factor is measured. Preliminary results from the analysis of the initial state radiation process e + e − → ppγ using a data set of 7.408 fb−1 collected at center-of-mass energies between 3.773 and 4.6 GeV, are also presented. The cross section for is measured based on 40.5 pb−1 data collected at 4 energy points from the threshold up to 3.08 GeV. Preliminary results on the total cross section and the Λ effective form factor are shown. Ongoing analysis based on the high luminosity energy scan from 2015 and from radiative return at different √s are also described.
Highlights
Electromagnetic form factors (FFs) describe the modifications of the point-like photon-hadron vertex due to the structure of the hadrons
Due to the fact that annihilation of e+e− is mostly accompanied by emission of one or several photons from the initial state, the high luminosity collected at the e+e− collider experiments, allows for a complementary approach to the energy scan technique in hadron cross section measurements: events with initial state radiation (ISR) photons lead to a reduction of the invariant mass (q2) allow for a measurement of the baryonic FFs over a wide of the range opfroqt2obne-alonwtip√rost.on system, and
A precise and complete measurement of the baryon FFs in this region is of great importance
Summary
Electromagnetic form factors (FFs) describe the modifications of the point-like photon-hadron vertex due to the structure of the hadrons They provide information on the intrinsic electric and magnetic distributions of hadrons. Due to the fact that annihilation of e+e− is mostly accompanied by emission of one or several photons from the initial state, the high luminosity collected at the e+e− collider experiments, allows for a complementary approach to the energy scan technique in hadron cross section measurements: events with ISR photons lead to a reduction of the invariant mass (q2) allow for a measurement of the baryonic FFs over a wide of the range opfroqt2obne-alonwtip√rost.on system, and. An electromagnetic calorimeter (EMC) consisting of 6240 CsI (Tl) in a cylindrical structure and two end caps is used to measure the energies of photons and electrons.
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