Measurement of the Proton Form Factor by Studying e⁺e⁻ → pp̅


Using data samples collected with the BESIII detector at the BEPCII collider, we measure the Born cross section of e⁺e⁻ → pp̅ at 12 center-of-mass energies from 2232.4 to 3671.0 MeV. The corresponding effective electromagnetic form factor of the proton is deduced under the assumption that the electric and magnetic form factors are equal |G(E)| = |G(M)|. In addition, the ratio of electric to magnetic form factors, |G(E)/G(M)|, and |G(M)| are extracted by fitting the polar angle distribution of the proton for the data samples with larger statistics, namely at √s̅ = 2232.4 and 2400.0 MeV and a combined sample at √s̅ = 3050.0, 3060.0 and 3080.0 MeV, respectively. The measured cross sections are in agreement with recent results from BABAR, improving the overall uncertainty by about 30%. |G(E)/G(M)| ratios are close to unity and consistent with BABAR results in the same q^2 region, which indicates the data are consistent with the assumption that |G(E)| = |G(M)| within uncertainties.



Particles (Nuclear physics, Astronomy, Astrophysics, Protons, Uncertainty, Brightness temperature

This work is supported in part by National Key Basic Research Program of China under Contract No. 2015CB856700; National Natural Science Foundation of China (NSFC) under Contracts Nos. 10935007, 11121092, 11125525, 11235011, 11322544, 11335008, 11375170, 11275189, 11078030, 11475164, 11005109, 11475169, 11425524; Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under Contracts Nos. 11079008, 11179007, U1232201, U1332201; CAS under Contracts Nos. KJCX2-YW-N29, KJCX2-YW-N45; German Research Foundation DFG under Contract No. Collaborative Research Center CRC-1044; Ministry of Development of Turkey under Contract No. DPT2006K-120470; Russian Foundation for Basic Research under Contract No. 14-07-91152; U. S. Department of Energy under Contracts Nos. DE-FG02-04ER41291, DE-FG02-05ER41374, DE-FG02-94ER40823, DESC0010118; WCU Program of National Research Foundation of Korea under Contract No. R32-2008-000-10155-0.


©2015 American Physical Society