The BESIII collaboration recently reported “Measurements of the Electric and Magnetic Form Factors of the Neutron for Timelike Momentum Transfer”, which has been published in Physical Review Letters on 14 April. [Phys. Rev. Lett. 130, 151905 (2023)].
The neutron electromagnetic form factors (EMFFs) represent the simplest structure observables, shed light on the fundamental building block of matter, and serve as a test ground for our understanding of the strong interaction with which nucleons are bound with each other, involving in both nuclear physics and hadron physics. In addition, the neutron EMFFs also serve a fundamental input in many different kinds of fundamental experiments.
For viewpoint of experiments, measurements of the neutron-antineutron pair are very challenging due to not only detection techniques but also instrumental calibration. That is why rare data with large statistics from annihilation reactions were available in the past. Using data collected in the c.m. energies from 2.0 to 2.95 GeV corresponding to an integrated luminosity of 354.6 pb-1, the differential cross-sections is measured and the first high precision measurement of separated electric and magnetic form factors of the neutron is achieved with comprehensive analysis methods. A pioneer work that measures the integrated cross-sections for the process of e+e-->nnbar has been published as a cover letter in Nature Physics on Nov. 08, 2011[Nat. Phys. 17, 1200–1204 (2021)]. This study fully exhibited the potential of studying the electromagnetic structure of nucleons taking facilities of both BEPCII and BESIII.
PRL Publication: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.130.151905