Tübingen 2003 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 13: Poster-Sitzung: Theorie

HK 13.2: Poster

Dienstag, 18. März 2003, 13:30–15:30, Foyer

Size and Shape of Baryons — •Alfons Buchmann — Universitaet Tuebingen, Institut fuer Theoretische Physik

Charge radii and quadrupole moments characterize the spatial extension and shape of baryons. Both aspects of baryon structure are shown to be closely related.

Baryon charge radii and quadrupole moments are calculated in a quark model generalized to an arbitrary number of colors. Several relations among baryon charge radii and quadrupole moments are found. Some of these are shown to be general consequences of the underlying symmetries of QCD.

Furthermore, we find an interesting relation between the neutron charge radius and the N → Δ quadrupole moment that is in good agreement with experiment. We show that this relation holds independent of the number of colors.

The geometric shape of the nucleon is determined by its intrinsic quadrupole moment. We calculate this quantity in various models of nucleon structure. All our models lead to the same conclusion, namely a prolate (cigar-shaped) nucleon and an oblate (pancake-shaped) Δ(1232).

We also discuss several methods for measuring baryon quadrupole moments and the prospects for such measurements.