Baryon Structure in QCD

R. Babich, J. Howard, C. Rebbi, Department of Physics and Center for Computational Science, Boston University, USA
F. Berruto, Department of Physics, Brookhaven National Laboratory, USA
C. Hoelbling, Department of Physics, Bergische Universität Wuppertal, Germany
N. Garron, DESY, Zeuthen, Germany
L. Lellouch, Centre de Physique Théorique, CNRS Luminy, Marseille, France
N. Shoresh, Bauer Center for Genomics Research, Harvard University

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Figure 1 – Geometry used for the visualization of the diquark wave-functions.

Quantum Chromodynamics (QCD) describes the structure of nuclear particles in terms of quarks and gluons. Baryons, such as protons and neutrons, are made of three quarks. Numerical simulations using Boston University’s IBM p690 and BlueGene supercomputers are used to study the quantum motion of quarks inside baryons. In particular, on theoretical grounds it has been argued that pairs of quarks would bind together in entities called diquarks, with a tighter binding if the spins of the two quarks are anti-aligned forming the so called good diquark, than if they are aligned (bad diquark). The calculations done at Boston University provide strong support for this conjecture. The figures show the quantum mechanical wave-function of a u-d diquark inside the baryon.

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Figure 2 – Wave-functions of the good u-d diquark (red) and bad u-d diquark (green), in the x-y plane of relative coordinates of the u and d quarks at fixed mean distance from the s quark.

The geometry is illustrated in Figure 1. The central point of the u, d quark pair is taken at a fixed distance from the s quark. The wave-functions of the good diquark (red) and of the bad diquark (green) are then shown, superimposed, in the lower figure, which clearly shows that the binding of the two quarks is tighter in the good diquark than in the bad diquark. Diquarks can be used to explain many experimental properties of baryons.

 

Visualization Movie

This movie was originally shown in stereo on our traveling high-resolution stereo display at the Supercomputing 2006 conference at a resolution of 2048 x 1536. For the web version here, it has been downsampled to 720 x 540 mono and is available in the Microsoft AVI and Apple Quicktime video formats.

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The movie illustrates the wave-functions of the u-d diquarks as the distance from the s quark progressively increases. (3MB AVI, 12MB QuickTime)