We have studied the three quark system in a relativized version of the quark potential model with chromodynamics. With parameters consistent with those of an analogous study of meson spectroscopy we obtain a successful description of the spectrum of baryons. The model naturally explains the apparent absence of spin‐orbit interactions in baryons.

Baryons in a relativized quark model with chromodynamics

Annalen der Physik

Since Millikan's famous oil-drop experiments1, it has been well known that electrical charge is quantized in units of the charge of an electron, e. For this reason, the theoretical prediction2,3 by Laughlin of the existence of fractionally charged ‘quasiparticles’—proposed as an explanation for the fractional quantum Hall (FQH) effect—is very counterintuitive. The FQH effect is a phenomenon observed in the conduction properties of a two-dimensional electron gas subjected to a strong perpendicular magnetic field. This effect results from the strong interaction between electrons, brought about by the magnetic field, giving rise to the aforementioned fractionally charged quasiparticles which carry the current. Here we report the direct observation of these counterintuitive entities by using measurements of quantum shot noise. Quantum shot noise results from the discreteness of the current-carrying charges and so is proportional to both the charge of the quasiparticles and the average current. Our measurements of quantum shot noise show unambiguously that current in a two-dimensional electron gas in the FQH regime is carried by fractional charges—e/3 in the present case—in agreement with Laughlin's prediction.

Direct observation of a fractional charge

Classical nuclear theory deals with a many-body system of neutrons and protons interacting nonrelativistically through two-body potentials. It has, of course, long been realized that there must be corrections to this simple picture—for example, the meson exchange effects which preclude a simple interpretation of the magnetic moment of the deuteron in terms of d-state probability. Nevertheless, the availability of beams of pions, and the consequent ability to study the excitation of real isobars in nuclei, has been critical in the realization that for many problems one must develop a theoretical model which explicitly includes pion and isobar degrees of freedom (see, for example, the proceedings of recent topical conferences Cat+ 82, MT 80).

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Chiral Symmetry and the Bag Model: A New Starting Point for Nuclear Physics

The Z-pinch, perhaps the oldest subject in plasma physics, has achieved a remarkable renaissance in recent years, following a few decades of neglect due to its basically unstable MHD character. Using wire arrays, a significant transition at high wire number led to a great improvement in both compression and uniformity of the Z-pinch. Resulting from this the Z-accelerator at Sandia at 20 MA in 100 ns has produced a powerful, short pulse, soft x-ray source >230 TW for 4.5 ns) at a high efficiency of ~15%. This has applications to inertial confinement fusion. Several hohlraum designs have been tested. The vacuum hohlraum has demonstrated the control of symmetry of irradiation on a capsule, while the dynamic hohlraum at a higher radiation temperature of 230 eV has compressed a capsule from 2 mm to 0.8 mm diameter with a neutron yield >3 × 1011 thermal DD neutrons, a record for any capsule implosion. World record ion temperatures of >200 keV have recently been measured in a stainless-steel plasma designed for Kα emission at stagnation, due, it was predicted, to ion-viscous heating associated with the dissipation of fast-growing short wavelength nonlinear MHD instabilities. Direct fusion experiments using deuterium gas-puffs have yielded 3.9 × 1013 neutrons with only 5% asymmetry, suggesting for the first time a mainly thermal source. The physics of wire-array implosions is a dominant theme. It is concerned with the transformation of wires to liquid-vapour expanding cores; then the generation of a surrounding plasma corona which carries most of the current, with inward flowing low magnetic Reynolds number jets correlated with axial instabilities on each wire; later an almost constant velocity, snowplough-like implosion occurs during which gaps appear in the cores, leading to stagnation on the axis, and the production of the main soft-x-ray pulse. These studies have been pursued also with smaller facilities in other laboratories around the world. At Imperial College, conical and radial wire arrays have led to highly collimated tungsten plasma jets with a Mach number of >20, allowing laboratory astrophysics experiments to be undertaken. These highlights will be underpinned in this review with the basic physics of Z-pinches including stability, kinetic effects, and finally its applications.

A review of the dense Z-pinch

A Model of Baryons Made of Quarks with Hidden Spin

The meaning of Lorentz contraction in special relativity and its connection with Bell's spaceships parable is discussed. The motion of Bell's spaceships is then compared with the accelerated motion of a rigid body. We have tried to write this in a simple form that could be used to correct students' misconceptions due to conflicting earlier treatments.

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Lorentz contraction, Bell’s spaceships and rigid body motion in special relativity

There are two baryons at the center of an octet weight diagram of S${\mathrm{U}(3)}_{\mathrm{flavor}}$ both of which contain the same quarks. We call these baryons "flavor degenerate." We discuss the symmetry of the wave functions of these baryons in terms of a quark-ordering principle and a mixing angle. We explore the consequences of the mixing on predictions of the masses and magnetic moments of flavor-degenerate baryons, including baryons containing heavy quarks. We obtain a simple approximate expression for the mixing angles in terms of the quark masses. The mixing angles turn out to be rather small, but still change some of the calculated magnetic moments substantially. The effect of mixing on the baryon masses is much smaller.

Wave Function Mixing of Flavor Degenerate Baryons

The mixing angle between the {Xi}{sub c} and {Xi}{sub c}{sup {prime}} baryons is shown to be small in quark model calculations, with a negligible shift in the {Xi}{sub c} masses. {copyright} {ital 1997} {ital The American Physical Society}

Mixing of Xi(c) - Xi(c)-prime baryons

Baryon magnetic moments and beta decay ratios ${(G}_{A}{/G}_{V})$ are calculated in a phenomenological quark model. Nonstatic effects of pion exchange and orbital excitation are included. Good agreement with experiment is found for a combined fit to all measured baryon magnetic moments and beta decay ratios. The model predicts an antiquark content for the proton that is consistent with the Gottfried sum rule.

Jerrold Franklin

Papers

A Model of Baryons Made of Quarks with Hidden Spin

Lorentz contraction, Bell’s spaceships and rigid body motion in special relativity

Wave Function Mixing of Flavor Degenerate Baryons

Mixing of Xi(c) - Xi(c)-prime baryons

Phenomenological quark model for baryon magnetic moments and beta decay ratios (GA/GV)