Hypernuclear production with a strong spin-flip

A kinematically correct treatment of the full transition amplitude for many-body hypernuclear production is presented. By an example of (⁺, K⁺) reaction, effects of the spin-flip amplitude and its interference with the spin-non-flip amplitude are demonstrated and specified for ¹² C.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.The discussions with many colleagues are appreciated, in particular those with R. Mach, L. Majling and T. Motoba were of much use.     

Model-independent result for the imaginary part of forward πHe4 scattering amplitude in unphysical region

Evaluation of contributions from dispersion integrals to the real part of forwardHe⁴ scattering amplitude is reconsidered. By application of a generalized mean-value theorem to the dispersion integral from the lowest branch point to the elastic threshold, a model-independent conclusion on the imaginary part of forwardHe⁴ scattering amplitude in unphysical region is drawn.     

The running of the electromagnetic coupling $\alpha$ in small angle Bhabha scattering

A method to determine the running of from a measurement of small angle Bhabha scattering is proposed and worked out. The method is suited to high statistics experiments at e ⁺ e^--colliders which are equipped with luminometers in the appropriate angular region. A new simulation code predicting small angle Bhabha scattering is also presented.Received: 22 January 2004, Published online: 16 March 2004L. Trentadue: Permanent address: Dipartimento di Fisica, Universitá di Parma and INFN, Gruppo Collegato di Parma, 43100 Parma, Italy     

Phase-modulus correlations for forward-scattering amplitudes without the Froissart bound

The role of the Froissart-Martin bound in obtaining rigorous phase-modulus asymptotic correlations for forward scattering is examined. A general form of the asymptotic upper bound on the total cross section covering the majority of cases occuring in weak interactions as well as in model field theories is assumed and its consequences for the asymptotic- correlations are drawn, being the ratio ReF/ImF for the crossing-even forward scattering amplitudeF. It is shown that the form of the correlations depends in an essential way on the absolute bound on assumed. Generalizations to the crossing-odd amplitude as well as to non-forward scattering are pointed out.On leave of absence from theAll Union Polytechnical Institute, Moscow, Pavel Korchagin Street, 22, USSR.Discussions with V.Alda, P.Kolá and R.ály are gratefully acknowledged.     

Analysis of proton elastic scattering from16O and40Ca at 800 MeV within the α-particle model

Elastic scattering of proton from¹⁶O and⁴⁰Ca are analyzed within the -particle model. The results are in good agreement with the experimental data. The role displayed by the phase factor ofp- scattering amplitude is investigated.     

The electron paramagnetic resonance in reduced BaTiO3 crystals

The electrcn-spin resonance of reduced BaTiO₃ crystals, which was studied by Z. roubek and K. d'ánský [Czech. J. Phys.B 13 (1963), 309], is interpreted as the resonance of the Ti³⁺ ion. The facts which favour this interpretation are discussed. The distortion of the oxygen ions surrounding the Ti³⁺ ion has been taken into account in order to explain the measured electron paramagnetic resonance spectrum. Considering the crystal-field model of C_4v point-group symmetry, the Stark energy-level separations of the Ti³⁺ ion and the values of theg factors are calculated.The authors would like to thank Dr. E. imánek for many very helpful discussions and Dr. H. Arend for helpful comments.     

Über die Amputierung der Vertexfunktionen instabiler Teilchen

The normalized form of the amputated vertex functions of an unstable particle is derived from the requirement that the general Ansatz (1) for the scattering amplitude of two stable particles with a resonance in the energy-variable is unitary in the energy interval below the threshold for three particle production. A Klein-Gordon equation for the unstable particle associated with the resonance is derived. The results a re applied to the creation of ⁺ and ⁰ mesons in inelastic scattering processes.     

Investigation of7Be(n,p)7Li reaction

The⁷Be(n, p)⁷Li nuclear reaction with thermal and 2 keV neutrons was studied. For thermal neutrons the total cross section of (46 800± 4 000) b was obtained and the proton branching ratio to the first excited and ground states of⁷Li was determined to be ₁/₀ = (2±1) %. For 2 keV neutrons the upper limit of the cross section of 540 b was estimated.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.The autors thank Mr. A. Dvoák and Mrs. B. Michalcová for their manufacturing the⁶Li standards, Dr. J. Frána for his help in determining the number of⁷Be atoms and Ing. J. Hoffmann, Mr. J. Novotný and Mr. J. Badura for their careful preparation of electronics.     

Asymptotics of the binary amplitude for a model Faddeev equation

A model equation obtained from the s-wave Faddeev equation in configuration space for three identical bosons by replacing the inhomogeneous integral term with a known function is studied. This function simulates the asymptotic decrease of the inhomogeneous term in the original Faddeev equation when y → ∞ as ～y^–3/2. The asymptotes of the amplitude functions that approach the scattering amplitudes when y → ∞ are obtained analytically for the model equation using the Green function. It is shown that the asymptotics of the binary channel amplitude function oscillates. The similar oscillating behavior of the binary amplitude function is numerically demonstrated for the original s-wave Faddeev equation describing the neutron–deuteron scattering process.     

The real part of the amplitude of proton-deuteron scattering at an energy 3 GeV

Measurement of the differential cross-sections of the proton-deuteron scattering at 3 GeV is described. Measurement was performed in the region of angles 2.5° to 11.5°. Analysis of the experimental data shows that besides the imaginary scattering amplitude a real part of the scattering amplitude is also required to describe proton-deuteron scattering at 3 GeV energy; the magnitude of the real part is 28% of the imaginary part.Behová 7, Praha 1, Czechoslovakia.We gratefully acknowledge the assistance of the JINR staff and their valuable services.     

Far infrared properties of SbSI-SbSeI mixed crystals

Far infrared reflectivity of eight SbS_1–x Se _x I mixed single crystals was measured in 50–400 cm^–1 region in polarized light at 25 and –170 C. While the low-frequency ferroelectric mode shows clear one-mode behaviour the second B_1u mode in 126–180 cm^–1 region shows two-mode behaviour. The existence of local and gap modes in this case is discussed.The author thanks ing. K.Nejezchleb from College of Chemical Technology in Pardubice for the crystals, L.Novák for helpful discussions, Z.Híová for computations and N.Dvoáková for help and figure drawing.     

On the elastic scattering of proton on deuteron at an energy of 8·2 GeV

The elastic scattering of a proton on a deuteron at an energy of 8·2 GeV was studied by the method of nuclear photoemulsions. A stack, composed of 20 emulsions of the type NIKFI-R diluted with heavy water, was irradiated with an internal beam of protons on the synchrophasotron in the Joint Institute of Nuclear Research in Dubna. The beam was perpendicular to the plane of the emulsion and had an intensity of (3·36±0·10)×10⁵ protons/cm².Altogether 114 events of elastic scattering (p-d) and 62 events of elastic scattering (p-p) were found. The differential cross-section of elastic scattering (p-d) was determined in a range of scattering angles of 1–3° to 10° in CMS. The total cross-section of elastic scattering (p-d) in this range of angles was found to be _el =(9·74±1·10) mb.The effective radius of interaction between the proton and deuteron during elastic scattering was found to beR=(2·25±0–10)×10^–13 cm.Last but not least, he thanks the management of the Joint Institute of Nuclear Research in Dubna for irradiating the emulsions and M. G. afranová for valuable advice and unstinting help in irradiating the emulsions.     

Scattering of positive kaons by lightest nuclei on the basis of dispersion methods

Elastic scattering of low-energy positive kaons by²H,³He, and⁴He is considered in terms of theN/D equations, the inverse amplitude method, and the dispersionK-matrix approach. The influence of the Coulomb effects and of the multiple scattering terms on the partial-wave amplitudes has been studied. The calculated values ofK ⁺ d andK ^{+ 4}He scattering lengths are 0·45 fm and 0·48 fm respectively. The Coulomb effects contribute about 20% to the Coulombnuclear part of the amplitude for the kaon energy of 5–20 MeV.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

Luminescent properties of A1N activated by europium

The concentration and temperature dependence of emission and excitation spectra was measured on powder A1NEu phosphors. It was shown that A1N: Eu has two luminescent modifications which depend on the activator concentration. At low activator concentration the wide emission band is found in the blue-green region, while at high concentration it is in green region. The excitation spectra of A1NEu consist of wide bands extended from 40×10³ cm^–1 to 22 × × 10³ cm^–1. The emission and excitation spectra are interpreted as transitions between energy levels of Eu²⁺ ions (4f⁷4f⁶ 5d transitions). The structure of the Eu²⁺ luminescent centres and the temperature dependence of luminescence are discussed.The authors thank Dr. M.Polcarová for the RTG measurements and Mrs. I.Míková for the spectral analysis of the A1N: Eu samples. The authors are also grateful to Prof. M.Trlifaj, Dr. J.Pastrák and Dr. J.Kubátová for valuable discussions.     

Padé-approximant techniques for processing scattering data II. Energy-dependent phase-shift analysis of low-energy4He +2H scattering

The general method for Padé-parametrization of experimental scattering data proposed by the authors recently has been applied to analytic parametrizations of theS-matrix and of partialwave amplitudes with the aim of carrying out an energy-dependent phase-shift analysis. It has been shown that the high universality and flexibility of the Padé-approximants make it possible to describe the partial-wave amplitudes by a very small number of parameters (say 2–3 in each partial wave) and to create a universal scheme for parametrization of the full reaction amplitude based on the following hybrid approach: the energy dependence of the inner partial amplitudes is represented by Padé approximants whereas the peripheral part of the full amplitude is taken from the low-order iterations of the exact many-particle Faddeev —Yakubovsky equations. As an example of the technique an energy-dependent phase-shift analysis of low-energy²H +⁴He scattering has been carried out and the parameters of the 3⁺ 0,2⁺ 0 and 1⁺ 0 resonant states of⁶Li have been obtained together with the value of the vertex constant of the virtual decay⁶Li_g.s. ⁴He +²H. The values of the energy and width obtained from experimental data of the 2⁺ 0 and particularly of the 1⁺ 0 level differ significantly from the values published in the literature.Dedicated to Professor J. Kvasnica on the occasion of his sixtieth birthday.     

Nuclear forward scattering of synchrotron radiation from unmagnetized α-57Fe

Nuclear foward scattering of synchrotron radiation from magnetically polycrystalline and partly magnetized -⁵⁷Fe foils has been observed. The forward scattering amplitude in both cases is calculated. The results allow the interpretation of the time spectra from samples which are magnetically polycrystalline or exhibit an unidirectional magnetic texture.     

The effect of inelastic processes on theP 11 phase shift inπN scattering

Assuming that the nucleon is a bound state in the N system we derive the approximate formula for a phase shift in theP ₁₁ wave. The left-hand cut is approximated by two poles and the effect of inelastic processes on the scattering amplitude of the partial waveP ₁₁ is discussed in terms of Froissart's method. The values of the inelastic parameter are taken from the experimental data. In this way the agreement with the experimental values of the phase shift in theP ₁₁ wave for low energies can be obtained.The author thanks Dr. M. Petrá for a valuable discussion and Mr. M. Noga for a discussion of the calculations.     

Forward hadron-hadron scattering at high energy

The high energy elastic scattering of pp, , pπ⁺, pπ⁻, pk⁺ andpk ⁻ processes is studied at forward directions. The expressions for total scattering cross-sections and the ratios of real-to-imaginary parts of the forward amplitude are derived inP+f model. For the Regge part of the scattering amplitude, the standard form is taken. For the pomeron part, the Harari-Freund conjecture is assumed. The background is assumed to get dominant contributions from the multiparticle exchanges in that channel. These contributions are obtained by parametrising the branch cuts by conformal mapping and polynomial expansion methods. The agreement with the experiment is good. The fits suggest strong exchange degeneracy forpp andkp which in turn is consistent with the Harari-Freund duality.     

Electrical conductivity and thermoelectric power of heavily doped P-type CdSb

The electrical conductivity, the Hall effect and the thermoelectric power were studied in thec andb crystallographic directions as a function of the temperature on CdSb single crystals strongly doped with silver. The anisotropy of the electrical conductivity and the mobility of the holes and their mechanism of scattering on lattice vibrations and ionized acceptors are discussed and the density of states effective mass of holes is determined as a function of the temperature. The origin of the anisotropy of the hole mobility and the model of the CdSb valency band are considered.The authors thank Prof. J. Tauc and V. Frei for advice and stimulating discussions, V. Míková, J. Beránková and J. Kapar for preparing the CdSb single crystals and M. Neuvirtová and J. Mrávková for helping in the experimental work.     

The CNDO-MO study of oxygen impurity states in AlN crystal

Deep levels due to oxygen impurity have been theoretically studied by the quasimolecular approach. The calculation of the orbital spectra was performed using the CNDO/2 method. Some important quantities (transition energies, width of valence band, effective charges etc.) were estimated. The results obtained agree qualitatively well with experimental data but quantitatively are still about 20% in error. Some reasons for the above discrepancy are briefly discussed.The authors are very grateful to Dr. J.Kubátová and Dr. S.Paesová for helpful discussions of the experimental investigations of aluminum nitride and to Dr. J.Pastrák for his interest in this work and discussion of results.