 Cartoon illustration of a lattice QCD calculation, from the 2007 Nuclear Science Long Range Plan, by NSAC. Drawn by Joshua G. Rubin. |
 Cartoon of lepton scattering from a quark in the proton, showing also a q-qbar pair and the gluon vacuum. From a calculation by D. Leinweber (Adelaide). |
 Calculated proton spin dependent densities, from Gerry Miller (Washington) |
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One ought to be concerned about
our lack of detailed
understanding of the structure of the nucleon.
While almost all of our mass comes from the nucleons,
the proton and neutron, bound in atomic nuclei,
the nucleons are complex objects whose structure
largely cannot presently be predicted from the underlying
theory of Quantum Chromodynamics (QCD). The
naive quark model picture of the nucleon, as consisting
of 3 non-relativistic constituent quarks in s states,
is often misleading. I will discuss several aspects of
the nucleon's structure, and our modern understanding of
it, focusing on a simple property, the distribution of
charge and magnetization in the nucleon. Examples of
recently discovered counterintuitive aspects of the
nucleon structure include: the proton charge and
magnetization distributions are very different, the neutron
charge density is negative in the interior, and the nucleon shape
is in a sense deformed, even though it is a spherical object.
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