Reanalysis of Rosenbluth measurements of the proton form factors

We present a reanalysis of the data from Stanford Linear Accelerator Center (SLAC) experiments E140 [R. C. Walker et al., Phys. Rev. D 49, 5671 (1994)] and NE11 [L. Andivahis et al., Phys. Rev. D 50, 5491 (1994)] on elastic electron-proton scattering. This work is motivated by recent progress in calculating the corresponding radiative corrections and by the apparent discrepancy between the Rosenbluth and polarization transfer measurements of the proton electromagnetic form factors. New, corrected values for the scattering cross sections are presented, as well as a new form factor fit in the $Q^2$ range from 1 to 8.83 ${\text{GeV}}^2$. We also provide a complete set of revised formulas to account for radiative corrections in single-arm measurements of unpolarized elastic electron-proton scattering.

Figure 1

Three different predictions for the radiative tail in the case when $E_1=1$ GeV, $\theta ={70}^{\circ }$, and assuming dipole form factors. The elastic peak energy is $E_3^{\text{el}}=0.588$ GeV. The blue dashed line represents the cross section (21) based on the soft-photon approximation. The red solid line provides a better description of the radiative tail and is given by the sum of Eq. (22) with the terms from Eq. (21) proportional to $Z$ and $Z^2$. The points are simulated using the ESEPP (elastic scattering of electrons and positrons on protons) event generator [26] with the accurate QED model.

Figure 2

Results of the reanalysis in comparison with the original data for (a) $G_E/G_D$, (b) $G_M/\left(\mu G_D\right)$, and (c) $\mu G_E/G_M$ as functions of $Q^2$. The red solid lines represent the best fit to the cross-section data obtained using the parametrization (44, 45), while the shaded areas are the 68% confidence bands. The blue open and solid circles are the original data of Refs. [20] and [22], respectively. The black crosses (asterisks) illustrate how the individual data points reported in Ref. [20] (Ref. [22]) change after reanalysis. The gray dashed lines correspond to the Kelly parametrization [36]. Results of the polarization transfer measurements [11] (green squares), [13] (green triangles), and [14] (green inverted triangles) are also shown in panel (c).