Backward-Angle Electron-Proton Elastic Scattering and Proton Electromagnetic Form Factors

Abstract

Elastic electron-proton scattering cross sections were measured at backward angles (80"-90") in the laboratory for four-momentum transfers between 7 F -~ and 45 F-'. Experimental errors range from 3.1% to 5.3%, including a systematic error estimated to be 1.9% added in quadrature. Electric and magnetic form factors are computed from all the recent data in this q2 range, with allowance made for possible normalization differences. The results show a deviation from the scaling law.

Nucleon electromagnetic form factors

“…Figure 4 shows Rosenbluth separation results performed in the 1970's as the ratio G Ep /G D , where G D is the dipole FF given below by Eq. 14; it is noteworthy that these results strongly suggest a decrease of G Ep with increasing Q 2 , a fact noted in all four references [Ber71,Pri71,Bar73,Han73]. As will be seen in section 3.4, the slope of this decrease is about half the one found in recent recoil polarization experiments.…”

“…All cross section measurements have been single arm experiments, (e, e ′ ), except three early experiments at Cambridge [Pri71,Han73] and DESY [Bar73] in which both proton and electron were detected, (e, e ′ p), and the most recent one of Qattan et al [Qat05], in which only the proton was detected, (e, p). In all cases, measured raw cross sections need to be corrected for QED processes to first order in α ∼ 1/137, before accessing the cross section corresponding to one-photon-exchange, or Born term.…”

Neural network parameterizations of electromagnetic nucleon form-factors

“…The fit to TPE corrected data is given by 1-3-1 network (violet line), the data (red points) is taken from [70]. The fit to "old Rosenbluth data" (green points) is given by 1-1-1 network (violet line), the data is taken from [71,[78][79][80][81][82][83][84][85][86]. The fit uncertainty is computed with eq.…”

“…[70]). However, to see the TPE effect we consider also the original, (called here old Rosenbluth data) G M p /µ p G D [71,[78][79][80][81][82][83][84][85][86] and G Ep /G D [71, 78-84, 87, 88] data sets. 4 The neutron form-factor data (G En and G M n ) are obtained from…”

Interpretation of the flavor dependence of nucleon form factors in a generalized parton distribution model

“…(4a,4b), which define the Dirac and Pauli form factors, respectively, and fitted the remaining parameters, α q and p q in the Regge term in Eq. (6), to the available proton and neutron form factors [31][32][33][34][35].…”