Structure of the nucleon from electromagnetic space-like and time-like form factors

Abstract

Recent experimental data on space-like and time-like form factors of the nucleon are reviewed in light of a model of the nucleon with an intrinsic (quark-like) structure and a meson cloud. The analysis points to the astonishing result that the proton electric space-like form factor vanishes at Q^2~8 (GeV/c)^2 and becomes negative beyond that point. The intrinsic structure is estimated to have a r.m.s. radius of ~0.34 fm, much smaller than the proton r.m.s. radius ~0.82 fm. The calculations are in perfect agreement with space-like proton data, but deviate drastically from space-like neutron data at Q^2>1 (GeV/c)^2. Analysis of the time-like data appears to indicate excellent agreement with both proton and neutron data in the entire range of measured q^2=-Q^2 values.

Invited talk at the Workshop on e+e- in the 1-2 GeV range, Alghero, Italy, September 2003 (eConf C0309101); misprints corrected in Eqs. (14) and (15)

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• Measurements of GEn/GMn from the ^2H(vec{e},e'vec{n})^1H Reaction to Q^2=1.45 (GeV/c)^2

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