Near-threshold η production in the <Emphasis Type="Italic">pd</Emphasis>→<Emphasis Type="Italic">pd</Emphasis>η reaction

The total cross section of the pd→pdη reaction has been measured at two energies near threshold by detecting the final proton and deuteron in a magnetic spectrometer. The values are somewhat larger than expected on the basis of two simple theoretical estimates. Received: 23 March 2000     

Non-eikonal corrections for the scattering of spin-one particles

The Wallace Fourier-Bessel expansion of the scattering amplitude is generalised to the case of the scattering of a spin-one particle from a potential with a single tensor coupling as well as central and spin-orbit terms. A generating function for the eikonal-phase (quantum) corrections is evaluated in closed form. For medium-energy deuteron-nucleus scattering, the first-order correction is dominant and is shown to be significant in the interpretation of analysing power measurements. This conclusion is supported by a numerical comparison of the eikonal observables, evaluated with and without corrections, with those obtained from a numerical resolution of the Schrödinger equation for d-⁵⁸ Ni scattering at incident deuteron energies of 400 and 700 MeV.Received: 4 December 2003, Published online: 10 August 2004PACS: 03.65.Nk Scattering theory - 24.70. + s Polarization phenomena in reactions - 25.10. + s Nuclear reactions involving few-nucleon systems - 25.40.Hs Transfer reactionsM.W. Gaber: Present address: Department of Radiological Sciences, St. Jude Childrens Research Hospital, 332 N. Lauderdale St., Memphis, TN 38105-2794, USA     

Elastic pion-deuteron scattering near the 3-3 resonance

Elastic pion-deuteron scattering at medium energies is analyzed on the basis of the Brueckner model, particular attention being paid to the kinematic approximations that have to be made. In contrast to an earlier Glauber-type calculation, the energy dependence of the large angle cross section is reasonably well reproduced.     

An analysis of pion-nucleus scattering lengths within an α-cluster model

Pion-nucleus s-wave scattering lengths are calculated from a multiple scattering series in terms of the π-α scattering length. Agreement on the level of 10–20% with the values obtained from mesic-atom data is achieved for all nuclei with A ≦ 20. This lends weight to the speculation that pion absorption on light nuclei takes place primarily on α-particle substructures.     

Ocean forecasting in terrain-following coordinates: Formulation and skill assessment of the Regional Ocean Modeling System

Systematic improvements in algorithmic design of regional ocean circulation models have led to significant enhancement in simulation ability across a wide range of space/time scales and marine system types. As an example, we briefly review the Regional Ocean Modeling System, a member of a general class of three-dimensional, free-surface, terrain-following numerical models. Noteworthy characteristics of the ROMS computational kernel include: consistent temporal averaging of the barotropic mode to guarantee both exact conservation and constancy preservation properties for tracers; redefined barotropic pressure-gradient terms to account for local variations in the density field; vertical interpolation performed using conservative parabolic splines; and higher-order, quasi-monotone advection algorithms. Examples of quantitative skill assessment are shown for a tidally driven estuary, an ice-covered high-latitude sea, a wind- and buoyancy-forced continental shelf, and a mid-latitude ocean basin. The combination of moderate-order spatial approximations, enhanced conservation properties, and quasi-monotone advection produces both more robust and accurate, and less diffusive, solutions than those produced in earlier terrain-following ocean models. Together with advanced methods of data assimilation and novel observing system technologies, these capabilities constitute the necessary ingredients for multi-purpose regional ocean prediction systems.     

Exact vortex nucleation and cooperative vortex tunneling in dilute Bose-Einstein condensates

With the imminent advent of mesoscopic rotating Bose-Einstein condensates in the lowest Landau level regime, we explore lowest Landau level vortex nucleation. An exact many-body analysis is presented in a weakly elliptical trap for up to 400 particles. Striking non-mean-field features are exposed at filling factors >1. For example, near the critical rotation frequency pairs of energy levels approach each other with exponential accuracy. A physical interpretation is provided by requantizing a mean-field theory, where 1/N plays the role of Planck's constant, revealing two vortices cooperatively tunneling between classically degenerate energy minima. The tunnel splitting variation is described in terms of frequency, particle number, and ellipticity.