Measurements of the Proton Elastic-Form-Factor Ratio<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>μ</mml:mi><mml:mi>p</mml:mi></mml:msub><mml:msubsup><mml:mi>G</mml:mi><mml:mi>E</mml:mi><mml:mi>p</mml:mi></mml:msubsup><mml:mo>/</mml:mo><mml:msubsup><mml:mi>G</mml:mi><mml:mi>M</mml:mi><mml:mi>p</mml:mi></mml:msubsup></mml:math>at Low Momentum Transfer

The roles played by mesons in the electromagnetic form factors of the nucleon are explored using as a basis a model containing vector mesons with coupling to the continuum together with the asymptotic Q 2 behavior of perturbative QCD. Specifically, the vector dominance model (GKex) developed by E. L. Lomon is employed, as it is known to be very successful in representing the existing high-quality data published to date. An analysis is made of the experimental uncertainties present when the differences between the GKex model and the data are expanded in orthonormal basis functions. A main motivation for the present study is to provide insight into how the various ingredients in this model yield the measured behavior, including discussions of when dipole form factors are to be expected or not, of which mesons are the major contributors, for instance, at low Q 2 or large distances, and of what effects are predicted from coupling to the continuum. Such insights are first discussed in momentum space, followed by an analysis of how different and potentially useful information emerges when both the experimental and theoretical electric form factors are Fourier transformed to coordinate space. While these Fourier transforms should not be interpreted as "charge distributions," nevertheless the roles played by the various mesons, especially those which are dominant at large or small distance scales, can be explored via such experiment-theory comparisons.

show abstract

“…II) together with the polarization data [38][39][40][41]. The R p data used in the fit were the polarization measurements of Refs.…”

Section: Results In Momentum Space Andmentioning

confidence: 99%

Role of mesons in the electromagnetic form factors of the nucleon

Crawford

Akdoğan

Alarcón³

et al. 2010

Phys. Rev. C

Self Cite

View full text Add to dashboard Cite

show abstract

“…The measurement of the two polarization components provides a very valuable additional observable, which helps to separate G e and G m . For the polarization transfer data [68][69][70][71][72][73][74][75][76][77][78][79], the overall normalization is less of an issue, as the observable of interest is a ratio of two polarizations.…”

Section: Datamentioning

confidence: 99%

Proton Charge Radius from Electron Scattering

Sick

2017

Atoms

View full text Add to dashboard Cite

Abstract:The rms-radius R of the proton charge distribution is a fundamental quantity needed for precision physics. This radius, traditionally determined from elastic electron-proton scattering via the slope of the Sachs form factor G e (q 2 ) extrapolated to momentum transfer q 2 = 0, shows a large scatter. We discuss the approaches used to analyze the e-p data, partly redo these analyses in order to identify the sources of the discrepancies and explore alternative parameterizations. The problem lies in the model dependence of the parameterized G(q) needed for the extrapolation. This shape of G(q < q min ) is closely related to the shape of the charge density ρ(r) at large radii r, a quantity that is ignored in most analyses. When using our physics knowledge about this large-r density together with the information contained in the high-q data, the model dependence of the extrapolation is reduced, and different parameterizations of the pre-2010 data yield a consistent value for R = 0.887 ± 0.012 fm. This value disagrees with the more precise value 0.8409 ± 0.0004 fm determined from the Lamb shift in muonic hydrogen.

show abstract

“…A number of recent experiments at Jefferson Lab and MIT-Bates [12,13,14,15,27,28] have measured the proton form factor ratio R up to Q 2 = 8. …”

Section: Polarization Transfer (Pt) Methodsmentioning

confidence: 99%