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<font color="#000099"><b><font color="#3333ff">Physics Seminar<br>
Friday, Oct. 21, 2011<br>
11:00AM<br>
CC Auditorium<br>
Cookies & Coffee 10:45AM<br>
<big><br>
</big></font></b></font><b><font color="#cc0000"><big>Christian Weiss
<br>
Jefferson Lab</big>
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<font color="#cc0000"><b>"Quantifying the Nucleon's Meson Cloud with
Transverse Charge Densities"</b></font></big><br>
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The transverse charge and current densities provide an objective
spatial representation of the nucleon's elastic form factors and
contain essential information on its partonic structure in QCD. They
are usually obtained as the two-dimensional Fourier transforms of the
form factors measured in electron scattering at spacelike momentum
transfer. We present a novel approach in which the transverse densities
are represented as dispersion integrals of the form factors in the
timelike region. This formulation relates the transverse distribution
of quarks in the nucleon's periphery to the well-known hadronic
exchange mechanisms and permits a fully quantitative assessment of
traditional notions such as the "pion cloud" and "vector meson
dominance." We summarize the present knowledge and outline how future
form factor measurements at JLab and other facilities could further
explore the role of mesons in the nucleon's periphery. We also show
that the transverse charge density in the pion can be reconstructed
with unprecedented accuracy from the timelike form factor measured in
e+e- annihilation experiments and reveals the presence of pointlike
quark-antiquark configurations at the center. [PRC82 (2010) 042201;
PRC84, 045205 (2011); PRD83 (2011) 013006]
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