Probabilistic quark-model approach to proton fragmentation

A probabilistic approach is formulated to study the behaviour of the incident hadron quark flavours in the fragmentation process of high energy protons in lowp _T reactions. Analysis of available data onpp collisions, mainly on hyperon and antibaryon multiplicities, leads to estimates of the probabilities for the different ways in which the incident valence quarks recombine into final hadrons. We find that all three incident quarks emerge in one and the same outgoing nucleon (or nucleon resonance) with probabilityA ₃=0.35–0.4, that two of them emerge in one baryon and the third in another hadron (mostly a meson or meson resonance) with probabilityA ₂=0.6–0.5, and that they emerge in three distinct hadrons (mostly mesons or meson resonances) with probabilityA ₁=0.05–0.1. We find good support for a very simple probabilistic picture of the fragmentation process.     

Challenges of structure determination of compound surfaces

Attention is drawn to challenges facing the structure determination of compound surfaces of growing complexity. Besides the questions of large unit cells and disorder, and of many independent atoms in the unit cells, one must address the determination of composition, compositional disorder and simultaneously coexisting structures. Of special concern is the issue of stability of complex and compound surfaces, and the resulting concerns about experimental surface preparation and reproducibility.     

The impact of the natural sciences on archaeology

This article reviews some of the applications of physics to the solution of archaeological problems. The use of magnetic, resistivity and electromagnetic surveying techniques for the location of buried features is described. Various methods of age determination are outlined while the problems associated with radiocarbon dating of organic material and thermoluminescent dating of pottery are discussed in detail. The techniques, including petrological examination, chemical analysis and isotopic analysis, employed in the physical examination of archaeological artefacts are described. Examples of the application of these techniques in establishing the source of the raw materials used in pottery, metal and stone implements and in elucidating the techniques of manufacture of pottery and metal objects are also given.     

LEED intensity analysis of the (1 × 5) reconstruction of Ir(100)

A new LEED structural analysis is carried out for the (1 × 5) reconstruction of Ir(100). It is based on a recent set of experimental I–V curves obtained with a computer-controlled video camera. Special attention is paid to reproducibility and reliability, and an R?factor analysis is now included. The previously preferred structure (a buckled top layer that is quasi-hexagonally close-packed and involves bridge sites) is confirmed with minor positional adjustments comparable to the uncertainty of the method. The other structural models that have been examined can clearly be rejected.     

A study of charge distributions in inelastic proton-proton collisions

Charge distributions for the secondaries from inelastic proton-proton collisions are studied by means of new data from an experiment at 12 and 24 GeV/c (2 m HBC at CERN). By comparison with π^±p data at 16 GeV/c, the inclusive charge distributions for the fragments of an incident proton and pion, respectively, are analysed. In addition, the cross sections for charge exchange between cms hemispheres are presented for the various charged-particle multiplicities. For events with no more than one neutral particle, charge and baryon exchange between cms hemispheres are compared to those between clusters. For the inelastic two-prong reactions, the two-dimensional distributions in longitudinal phase space are presented.     

Hyperfine structure of 5d 2 D 3/2 135,137Ba ions by collinear fast beam laser-rf double resonance spectroscopy

The hyperfine structure of the metastable 5d ² D _3/2 state has been measured with high precision by collinear laser-rf double resonance spectroscopy on fast^135,137Ba ion beams. The present data are about 100 times more accurate than those obtained by classical fast beam laser spectroscopy.