Realizing vector meson dominance with transverse charge densities
May, 201114 pages
Published in:
- Phys.Rev.C 84 (2011) 045205
e-Print:
- 1105.6364 [hep-ph]
Report number:
- NT@UW-11-08,
- JLAB-THY-11-1377
Citations per year
Abstract: (arXiv)
The transverse charge density in a fast-moving nucleon is represented as a dispersion integral of the imaginary part of the Dirac form factor in the timelike region (spectral function). At a given transverse distance b the integration effectively extends over energies in a range sqrt{t} ~< 1/b, with exponential suppression of larger values. The transverse charge density at peripheral distances thus acts as a low-pass filter for the spectral function and allows one to select energy regions dominated by specific t-channel states, corresponding to definite exchange mechanisms in the spacelike form factor. We show that distances b ~ 0.5 - 1.5 fm in the isovector density are maximally sensitive to the rho meson region, with only a ~10% contribution from higher-mass states. Soft-pion exchange governed by chiral dynamics becomes relevant only at larger distances. In the isoscalar density higher-mass states beyond the omega are comparatively more important. The dispersion approach suggests that the positive transverse charge density in the neutron at b ~ 1 fm, found previously in a Fourier analysis of spacelike form factor data, could serve as a sensitive test of the the isoscalar strength in the ~1 GeV mass region. In terms of partonic structure, the transverse densities in the vector meson region b ~ 1 fm support an approximate mean-field picture of the motion of valence quarks in the nucleon.Note:
- 14 pages, 12 figures
- 13.60.Hb
- 12.40.Vv
- 11.55.Fv
- 13.40.Gp
- Vector meson dominance
- electromagnetic form factors
- dispersion relations
- generalized parton distributions
- charge: density
- density: transverse
References(40)
Figures(14)