2022/12/14 by BESIII Collaboration, Ablikim, M., Achasov, M. N. +589
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex)
paper · doi:10.48550/arxiv.2212.07071
We present the first measurements of the electric and magnetic form factors of the neutron in the time-like (positive q2) region as function of four-momentum transfer. We explored the differential cross sections of the reaction e+e- → nn with data collected with the BESIII detector at the BEPCII accelerator, corresponding to an integrated luminosity of 354.6 pb-1 in total at twelve center-of-mass energies between √(s) = 2.0 - 2.95 GeV. A relative uncertainty of 18% and 12% for the electric and magnetic form factors, respectively, is achieved at √(s) = 2.3935 GeV. Our results are comparable in accuracy to those from electron scattering in the comparable space-like (negative q2) region of four-momentum transfer. The electromagnetic form factor ratio R\rm em≡ |GE|/|GM| is within the uncertainties close to unity. We compare our result on |GE| and |GM| to recent model predictions, and the measurements in the space-like region to test the analyticity of electromagnetic form factors.