Elastic Electron-Proton Scattering Research Articles

Form Factors and Two-Photon Exchange in High-Energy Elastic Electron-Proton Scattering.

We present new precision measurements of the elastic electron-proton scattering cross section for momentum transfer (Q^{2}) up to 15.75 (GeV/c)^{2}. Combined with existing data, these provide an improved extraction of the proton magnetic form factor at high Q^{2} and double the range over which a longitudinal or transverse separation of the cross section can be performed. The difference between our results and polarization data agrees with that observed at lower Q^{2} and attributed to hard two-photon exchange (TPE) effects, extending to 8 (GeV/c)^{2} the range of Q^{2} for which a discrepancy is established at >95% confidence. We use the discrepancy to quantify the size of TPE contributions needed to explain the cross section at high Q^{2}.

Cancellation of Leading Contributions to Radiative Corrections to the Cross Section for Elastic Electron–Proton Scattering in Experiments Devoted to Measuring the Proton Charge Radius

A cancellation of leading contributions to radiative corrections to the cross section for elastic electron–proton scattering for experiments devoted to measuring the proton charge radius is studied. The cancellations occur in the contribution of electron interaction with the electromagnetic field. It is shown that, under experimental conditions where the recoil proton is detected, there occurs cancellation in the one-loop approximation not only for the terms containing large logarithms but also for the constants at these logarithms and that a nonzero electron contribution to radiative corrections appears starting from terms that are proportional to $$Q/E$$ , where $$Q$$ is the momentum transfer and $$E$$ is the electron energy in the rest frame of the primary proton.

Two-Photon Exchange in Elastic Electron-Proton Scattering: A QCD Factorization Approach

We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer Q(2). It is shown that the leading two-photon exchange amplitude behaves as 1/Q(4), and can be expressed in a model independent way in terms of the leading twist nucleon distribution amplitudes. Using several models for the nucleon distribution amplitudes, we provide estimates for existing data and for ongoing experiments.

Two-Photon-Exchange Correction to Parity-Violating Elastic Electron-Proton Scattering

Higher-order QED effects play an important role in precision measurements of nucleon elastic form factors in electron scattering. Here we introduce a two-photon-exchange QED correction to the parity-violating polarization asymmetry of elastic electron-proton scattering. We calculate this correction in the parton model using the formalism of generalized parton distributions, and demonstrate that it can reach several percent in certain kinematics, becoming comparable in size with existing experimental measurements of strange-quark effects in the proton neutral weak current.

Normal Spin Asymmetries in Elastic Electron-Proton Scattering

We discuss the two-photon exchange contribution to observables which involve lepton helicity flip in elastic lepton-nucleon scattering. This contribution is accessed through the single spin asymmetry for a lepton beam polarized normal to the scattering plane. We estimate this beam normal spin asymmetry at large momentum transfer using a parton model and we express the corresponding amplitude in terms of generalized parton distributions. We further discuss this observable in the quasi-RCS kinematics which may be dominant at certain kinematical conditions and find it to be governed by the photon helicity-flip RCS amplitudes.

Measurement of the Transverse Beam Spin Asymmetry in Elastic Electron-Proton Scattering and the Inelastic Contribution to the Imaginary Part of the Two-Photon Exchange Amplitude

We report on a measurement of the asymmetry in the scattering of transversely polarized electrons off unpolarized protons, A( perpendicular), at two Q2 values of 0.106 and 0.230 (GeV/c)(2) and a scattering angle of 30 degrees <theta(e)<40 degrees . The measured transverse asymmetries are A( perpendicular)(Q(2)=0.106 (GeV/c)(2))=(-8.59+/-0.89(stat)+/-0.75(syst))x10(-6) and A( perpendicular)(Q(2)=0.230 (GeV/c)(2))=(-8.52+/-2.31(stat)+/-0.87(syst))x10(-6). The first errors denote the statistical error and the second the systematic uncertainties. From comparison with theoretical estimates of A( perpendicular) we conclude that piN-intermediate states give a substantial contribution to the imaginary part of the two-photon amplitude. There is no obvious reason why this should be different for the real part of the two-photon amplitude, which enters into the radiative corrections for the Rosenbluth separation measurements of the electric form factor of the proton.

Partonic calculation of the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer.

We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer through the scattering off a parton in the proton. We relate the two-photon exchange amplitude to the generalized parton distributions which appear in hard exclusive processes. We find that when taking the polarization transfer determinations of the form factors as input, adding in the 2-photon correction does reproduce the Rosenbluth cross sections.

Two-photon exchange and elastic electron-proton scattering.

Two-photon exchange contributions to elastic electron-proton scattering cross sections are evaluated in a simple hadronic model including the finite size of the proton. The corrections are found to be small in magnitude, but with a strong angular dependence at fixed Q2. This is significant for the Rosenbluth technique for determining the ratio of the electric and magnetic form factors of the proton at high Q2, and partly reconciles the apparent discrepancy with the results of the polarization transfer technique.

Parity violation in elastic electron-proton scattering and the Proton's strange magnetic form factor

We report a new measurement of the parity-violating asymmetry in elastic electron scattering from the proton at backward scattering angles. This asymmetry is sensitive to the strange magnetic form factor of the proton as well as electroweak axial radiative corrections. The new measurement of A = -4.92+/-0.61+/-0.73 ppm provides a significant constraint on these quantities. The implications for the strange magnetic form factor are discussed in the context of theoretical estimates for the axial corrections.

Elastic Electron-Proton Scattering at Large Four-Momentum Transfer

Electron-proton elastic-scattering cross sections have been measured at the Stanford Linear Accelerator Center for four-momentum transfers squared q^2 from 1.0 to 25.0 (GeV/c)^2. The electric (GEp) and magnetic (GMp) form factors of the proton were not separated, since angular distributions were not measured at each q^2. However, values for GMp were derived assuming various relations between GEp and GMp. Several theoretical models for the behavior of the proton magnetic form factor at high values of q^2 are compared with the data.

Contribution of Elastic Intermediate States to Polarization of the Recoil Proton in Elastic Electron-Proton Scattering

Contribution of Elastic Intermediate States to Polarization of the Recoil Proton in Elastic Electron-Proton Scattering

Proton Polarization in Elastic Electron-Proton Scattering

Proton Polarization in Elastic Electron-Proton Scattering

Elastic Electron-Proton Scattering Cross Sections Measured by a Coincidence Technique

We have measured elastic electron-proton scattering cross sections in the range of four-momentum transfers from 7 ${\mathrm{F}}^{\ensuremath{-}2}$[0.27 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$] to 150 ${\mathrm{F}}^{\ensuremath{-}2}$ [5.84 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$] and at scattered electron angles of between 20\ifmmode^\circ\else\textdegree\fi{} and 34\ifmmode^\circ\else\textdegree\fi{} in the laboratory. The estimated errors in the cross sections range from \ifmmode\pm\else\textpm\fi{}2.1% at the lowest momentum transfer to \ifmmode\pm\else\textpm\fi{}9.6% at the highest. Both the scattered electron and the recoil proton were detected, resulting in an overdetermination of the kinematics. When the constraint of a coincident proton is removed, there is no significant change in the estimated cross sections.

Measurement of the Polarization in Elastic Electron-Proton Scattering

We have measured the asymmetry in the elastic scattering of electrons from a polarized proton target. An interference between the imaginary part of the two-photon-exchange amplitude and the one-photon-exchange amplitude could produce a polarization effect. The results indicate no asymmetry within the experimental accuracy of 1 to 2% at four-momentum-transfer-squared values values of o.38, 0.59, and 0.98 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$.

Comparison of Elastic Electron-Proton Scattering Cross Sections with Some Theoretical Predictions

Comparison of Elastic Electron-Proton Scattering Cross Sections with Some Theoretical Predictions

Measurements of Elastic Electron-Proton Scattering at High Momentum Transfer by a Coincidence Technique

We present measurements of elastic electron-proton scattering cross sections in which both the scattered electron and recoil proton have been detected. Cross sections have been measured for a range of four-momentum transfers from 10 to 150 ${\mathrm{F}}^{\ensuremath{-}2}$ with an estimated accuracy of between $3\frac{1}{3}$ and 10%.

Proton Form Factors from Elastic Electron-Proton Scattering

Absolute measurements of the elastic electron-proton cross section have been made with a precision of about 4% for values of the square of the four-momentum transfer, ${q}^{2}$, in the range 6.0 to 30.0 ${\mathrm{F}}^{\ensuremath{-}2}$ and for electron scattering angles in the range 45\ifmmode^\circ\else\textdegree\fi{} to 145\ifmmode^\circ\else\textdegree\fi{}. To within the experimental errors, it is found that the charge and magnetic form factors of the proton have a common dependence on ${q}^{2}$ when normalized to unity at ${q}^{2}=0$, and that an accurate representation of the behavior of the form factor and that of the cross sections themselves can be given in terms of a three-pole approximation to the dispersion theory of nucleon form factors.

Notizen: The Influence of the f0 Meson in the Two-Photon Exchange on the Relative Ratio of σe - p to σe + p and the Polarization of the Recoil Protons in Elastic Electron-Proton Scattering

Article Notizen: The Influence of the f0 Meson in the Two-Photon Exchange on the Relative Ratio of σe-p to σe+p and the Polarization of the Recoil Protons in Elastic Electron-Proton Scattering was published on June 1, 1965 in the journal Zeitschrift für Naturforschung A (volume 20, issue 6).