Search

The π 0 momentum dependence of the decay η → π + π − π 0 has been measured with the Crystal Barrel detector. The analysis is based on 3230 events. The results of this independent measurement are compared to new chiral perturbation theory calculations and previous measurements.

We study phenomenologically the density dependence of the K − optical potential V opt ( r ) at zero kinetic energy by fitting it to a comprehensive set of atomic data across the periodic table. Two families of solutions offer improved fits over that for the standard t eff ϱ ( r ) paraameterization of V opt . One family contains solutions for V opt with RMS radii larger than those of the matter density ϱ , as expected from finite-range folding corrections. The other family offers substantially improved fits to the data and gives rise to Re V opt of a size smaller than that of ϱ . The new family contains solutions for which V opt is attractive inside the nucleus and on its surface, becoming repulsive at large distances. The repulsion can be made to approximately agree with the low-density limit V opt → tϱ where t is the free-space K N t matrix. It is argued that this sign flip might be expected from the underlying nuclear propagation of the Λ(1405).

The results of a measurement of pp annihilation at rest into ηηπ 0 are presented. Assuming a resonance dominated model for the annihilation process an isoscalar J PC =0 ++ resonance decaying into ηη is observed with a mass of 1560±25 MeV/ c 2 and a width of 245±50 MeV/ c 2 .

The crystal Barrel spectrometer used at LEAR, CERN to study the products of pd annihilations is described. A 1380 element array of Csl crystals measures photons from the decay of π0, η, η′ and ω mesons. A segmented drift chamber in a 1.5T magnetic field is used to identify and measure charged particles. A fast on-line trigger on charged and neutral multiplicities and on the invariant mass of secondary particles is available. The performance of the detector is discussed.

Experimental studies of antiprotonic-hydrogen atoms have recently made great progress following the commissioning of the low-energy antiproton facility LEAR at CERN in 1983. At the same time the understanding of the atomic cascade has increased considerably through measurements of the X-ray spectra. The life history of the p-p atom is considered in some detail, from the initial capture of the antiproton when stopping in hydrogen, through the atomic cascade with the emission of X-rays, to the final antiproton annihilation and production of mesons. The experiments carried out at LEAR are described and the results compared with atomic cascade calculations and predictions of strong interaction effects.

A systematic experimental study of strong interaction shifts, widths, and yields from high-Z kaonic atoms is reported. Strong interaction effects for the K-(8→7) transition were measured in U, Pb, and W, and the K-(7→6) transition in W was also observed. This is the first observation of two measurably broadened and shifted kaonic transitions in a single target and thus permitted the width of the upper state to be determined directly, rather than being inferred from yield data. The results are compared with optical-model calculations.

The multi-disciplinary role of intermediate energy proton accelerators in pure and applied nuclear physics is discussed with particular reference to the experimental programmes at LAMPF (Los Alamos Meson Physics Facility) and SIN (Swiss Institute for Nuclear Research, Zurich).

A method for determining the efficiency of a Si(Li) X-ray detector at low energies using a fluorescence X-ray source is described. The thickness of the Be X-ray window and of the Si dead layer can also be measured. Results obtained using the method are described and the effects of the gold contact and of a possible ice layer on the surface of the detector considered.

A reanalysis of the recent precision data for the scattering of 104 MeV $\ensuremath{\alpha}$ particles by $^{204,206,208}\mathrm{Pb}$ reveals a lower minimum in the ${\ensuremath{\chi}}^{2}$ fits than that originally obtained by Gils and Rebel. This lower minimum is associated with a more acceptable value for the diffuseness parameter of the imaginary potential. It leads to smaller rms radii for the neutron distributions, which are now found to be equal to the corresponding radii for protons to within \ifmmode\pm\else\textpm\fi{}0.1 fm.

The differential cross section for the scattering of 970 MeV protons by carbon through laboratory angles of 1½° to 5° has been measured using nuclear emulsions to detect the scattered particles. The results show a sharp rise at small angles due to the onset of Coulomb scattering and have been fitted at the larger angles (greater than 2°) in terms of a simple model in which the nucleus is represented by a purely imaginary central potential. Values for the diffraction and total cross sections are then derived. Preliminary results of a more detailed analysis, which includes a spin-orbit potential, shows that a fit can be obtained at all angles if a small negative real part to the central potential is included. Further evidence is found for polarization effects at these energies.

Nuclear emulsions have been used as detectors to measure the asymmetries produced in a double scattering experiment using 970 MeV protons. Targets of beryllium and carbon have been used and angles between 3° and 8° investigated. Small but significant asymmetries have been found and the experiments are compared with others in this energy region.

The optical model parameters for the scattering of 310 MeV protons by carbon are obtained in an analysis using the semi-classical approximation. The results are compared with those obtained by other analyses in this energy region. The modification of the Coulomb scattering by the absorption of protons in the nucleus is also considered in some detail.

The observation of neutron-antineutron transitions would be direct evidence for baryon number violation. For the first time an experiment has been carried out to search for this phenomenon with neutrons in free flight. The experiment using the research reactor at the Institut Laue-Langevin in Grenoble has set a lower limit to the oscillation time τ n n of 106 s.

The difverential cross section for the scattering at small angles of 970- Mev protons from carbon was measured in order to examine the interterence between the Coulomb and nuclear pasts of the scattering at this energy. The measurements were made at laboratory angles tom 1 to 3.75 . The proton beam of the Birmingham syachrotron was scattered from a carbon target Placed inside a vacuum box. (W..D.M.)

Fits to data on strong interaction level shifts and widths in pionic atoms, over the whole of the periodic table, are made with the Kemmer-Duffin-Petiau equation. Comparisons are made with the conventional Klein-Gordon equation and emphasis is placed on the problem of anomalously small shifts and widths. The Kemmer-Duffin-Petiau equation yields fits which are marginally better than those obtained with the Klein-Gordon equation.

An exotic atom is formed when an electron in an “ordinary” atom is replaced by a heavier particle such as a muon, π or K-meson, antiproton or a ∑-hyperon. Studies of these exotic atoms cover a whole range of disciplines from atomic and solid-state physics to nuclear and elementary particle physics. From the nuclear point of view, the strongly interacting pions, kaons, antiprotons and sigma-hyperons give information about the very low energy hadron-nucleus interaction and can in principle give further information about the nucleus such as the matter distribution. Information about the properties of the hadron, such as its mass or magnetic moment, and about the hadron-nucleon interaction can also be obtained.

From the earliest days of nuclear physics (Rut 11, Rut 14), the spatial extent of atomic nuclei and the radial distribution of nuclear charge and matter have received considerable attention. One obvious reason for this interest is the role of spatial perception in the macroscopic world and the natural desire to order and characterize things by their sizes and shapes. Beyond this mere description, however, these are fundamental properties of any physical system. It is a primary and appealing gross property of atomic nuclei that, unlike many other quantum systems, they possess a central region of generally uniform density and a reasonably sharp nuclear surface. The central uniform density, or “saturation” property, has its origin in the Pauli principle and the short-range repulsion of nucleons. The sharpness of the nuclear surface is a direct consequence of the short range of the strong interaction.

High Energy Nuclear Reactions By A. B. Clegg. (Oxford Library of the Physical Sciences.) Pp. vi+130. (Oxford: Clarendon Press; London: Oxford University Press, 1965.) 18s. net.