X-ray determination of the mean amplitudes of vibration and debye temperatures of some rare earth monochalcogenides

The x-ray diffraction intensities of Bragg reflections have been measured at room temperature for thulium selenide, samarium sulphide, samarium selenide and samarium telluride. On the basis of a common amplitude approximation, the Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. The values of the Debye temperatures and mean amplitudes of vibration are 176±16°K, 0·185 ± 0·017 Å (TmSe), 155 ± 7°K, 0·244 ± 0·012 Å (SmS), 153 ± 14°K, 0·221 ± 0·020 Å (SmSe) and 151 ± 20°K, 0·204 ± 0·027 Å (SmTe).     

Observation of ω → π0μ+μ− decay

The results of studying the mass spectrum of μ⁺μ^?γγ systems produced in π^?p collisions at 25 and 33 GeV/c presented. The wide-aperture magnetic spectrometer with a hodoscope γ-detector was used to identify muon pairs and photons. There is a clear peak in the mass spectrum which corresponds to the decay ω → π⁰μ⁺μ^? previously not observed. The branching ratio for the decay is estimated to be 9 × 10^?5 with a systematic error of 50%.     

Analysis of coefficient identification problems associated to the inverse Euler-Bernoulli beam theory

A rigorous investigation of the identification of a heterogeneousflexural rigidity coefficient in the Euler-Bernoulli steady-statebeam theory in the presence of a prescribed load is presented.Mathematically, this study is an extension to higher-order differentialequations of the coefficient identification problem analysedby Marcellini (1982) for the one-dimensional Poisson equation.In addition, various types of boundary conditions are discussed.Conditions for the well-posedness of these inverse problemsare established and, furthermore, numerical results obtainedusing a regularization algorithm are presented.     

A critical investigation of the effects of the radio frequency potential on the trapping of externally injected ions in ion trap mass spectrometry

The sensitivity of all ion trap mass spectrometry (ITMS) methods is dependent on the trapping efficiency of the instrument. For ITMS instruments utilizing external ion sources, such as laser desorption, trapping efficiency is known to depend on the phase and amplitude of the radio frequency (RF) potential applied to the ring electrode at the time of ion introduction. It is remarkable that, in a considerable body of literature, no consensus exists regarding the effects of these parameters on the efficacy of trapping externally generated ions. In this paper, a summary of the literature is presented in order to highlight significant discrepancies. New laser desorption ion trap mass spectrometry (LD-ITMS) data are also presented, from which conclusions are drawn in our effort to clarify some of the confusion. Copyright 1999 John Wiley & Sons, Ltd.     

Neutral decays of the η-meson

The partial widths of η-meson decays η→2γ, η→3π⁰ and η→π⁰γγ have been measured in a high accuracy experiment made at the IHEP accelerator with the hodoscope electromagnetic spectrometer GAMS-2000. An upper limit has been determined for the 3γ channel. The Dalitz plot of the η decay into 3π⁰ shows that the matrix element does not depend on the pion energy.     

Small |t|π− p charge exchange scattering at 40 GeV/c

π^? p→π⁰ n differential cross-sections have been measured in the region of small 4-momentum transfer at 40 GeV/c incident momentum. The experiment performed at the IHEP 70 GeV accelerator makes use of a hodoscope γ-spectrometer. Thet- dependence of the cross-section points to a dominance of the spin-flip amplitude.     

A study of π−p → f0n reaction at momenta up to 50 GeV/c

A mass spectrum of π^oπ^o system in the final state of π^?p → π^oπ^on reaction has been studied at the momenta 20 to 50 GeV/c. The experiments were performed at the 70 GeV IHEP accelerator. In the mass distribution there has been selected a peak corresponding to f^o meson production cross section decreases in the power form with the momentum. The differential cross section follows exponential dependence, exp (bt).The mass spectrum of unbounded π^oπ^o system is satisfactorily described with multireggeon diagram of the ? and π exchange.     

Neutral decays ofη′(958)

The partial widths of the η′(958) decays into 2γ, ωγ, 3π⁰ andηπ⁰π⁰ have been measured with the GAMS-2000 spectrometer at the 70 GeV IHEP accelerator. Upper limits for the η′ decays into 3γ, π⁰γγ, 2π⁰ and 4π⁰ have also been obtained. The slope of a linear matrix element for theG-parity violating decayη′→3π⁰ has been determined.