Scattering of spin waves by a rectilinear edge dislocation

The propagation of volume spin waves in an unbounded easy-axis magnet containing a rectilinear edge dislocation is studied theoretically. The spin-wave scattering amplitudes are calculated in the Born approximation. It is shown that the spin-wave scattering amplitude vanishes for certain values of the scattering angle. The dependence of the scattering angle on the angle of incidence of the spin waves is found for this case. The transport scattering cross section of spin waves is found. Fiz. Tverd. Tela (St. Petersburg) 40, 2056–2058 (November 1998)     

A complete measurement of spin-observables for intermediate-energy inclusive quasielastic polarized proton scattering from C

The complete set of Wolfenstein parameters, the polarization, the asymmetry of scattering and the unpolarized double-differential cross section are presented for inclusive quasielastic proton scattering from ¹²C at a central momentum transfer of q = 1.9 fm⁻¹ and incident energies of 290 and 420 MeV. The spin observables D₀, D_x, D_y and D_z as well as the longitudinal-to-transverse ratio of spin-flip probabilities are extracted from the data. Across the quasielastic continuum, the experimental data is compared to the variations expected from a single-scattering Fermi-gas approximation using the free NN amplitudes. Medium effects are evident in the pronounced quenching of the polarization parameter relative to the free value.     

A study of quasielastic neutrino interactions ν μ n → μ− p in the NOMAD experiment

In this note, we present preliminary results on the study of the quasielastic reaction ν _μ n → μ⁻ p using the full set of NOMAD neutrino data. We perform a measurement of the total cross section of this process, normalizing to deep-inelastic scattering events selected from the same data sample. The measured cross section is found to be about 20% smaller than the world average of previous bubble chamber experiments. The analysis is still in progress since it is important to estimate the systematic uncertainties. for the NOMAD Collaboration The text was submitted by the authors in English.     

Neutrino quasielastic scattering on nuclear targets Parametrizing transverse enhancement (meson exchange currents)

We present a parametrization of the observed enhancement in the transverse electron quasielastic (QE) response function for nucleons bound in carbon as a function of the square of the four momentum transfer (Q ²) in terms of a correction to the magnetic form factors of bound nucleons. The parametrization should also be applicable to the transverse cross section in neutrino scattering. If the transverse enhancement originates from meson exchange currents (MEC), then it is theoretically expected that any enhancement in the longitudinal or axial contributions is small. We present the predictions of the “Transverse Enhancement” model (which is based on electron scattering data only) for the ν _μ , [`(n)]_m\bar{\nu}_{\mu} differential and total QE cross sections for nucleons bound in carbon. The Q ² dependence of the transverse enhancement is observed to resolve much of the long standing discrepancy in the QE total cross sections and differential distributions between low energy and high energy neutrino experiments on nuclear targets.     

Effects of short-range correlation and distortion in the reaction 4He(e,e′p)3H

An attempt is made to give a coherent explanation of the elastic and quasielastic electron scattering from ⁴He. It is shown that the short-range correlations and distortion effects in the reaction ⁴He(e, e′p)³H modify qualitatively the cross section for large momentum.     

Effective spectral function for quasielastic scattering on nuclei

Spectral functions that are used in neutrino event, generators to model quasielastic (QE) scattering from nuclear targets include Fermi gas, Local Thomas Fermi gas (LTF), Bodek-Ritchie Fermi gas with high momentum tail, and the Benhar-Fantoni two dimensional spectral function. We find that the \(\nu \) dependence of predictions of these spectral functions for the QE differential cross sections ( \({d^2\sigma }/{dQ^2 d\nu }\) ) are in disagreement with the prediction of the \(\psi '\) superscaling function which is extracted from fits to quasielastic electron scattering data on nuclear targets. It is known that spectral functions do not fully describe quasielastic scattering because they only model the initial state. Final state interactions distort the shape of the differential cross section at the peak and increase the cross section at the tails of the distribution. We show that the kinematic distributions predicted by the \(\psi '\) superscaling formalism can be well described with a modified effective spectral function (ESF). By construction, models using ESF in combination with the transverse enhancement contribution correctly predict electron QE scattering data.     

Spin structure of the “Forward” nucleon charge-exchange reaction <Emphasis Type="Italic">n</Emphasis> + <Emphasis Type="Italic">p</Emphasis> → <Emphasis Type="Italic">p</Emphasis> + <Emphasis Type="Italic">n</Emphasis> and the deuteron charge-exchange breakup

The structure of the nucleon charge-exchange process n + p → p + n is investigated basing on the isotopic invariance of the nucleon-nucleon scattering. Using the operator of permutation of the spin projections of the neutron and proton, the connection between the spin matrices, describing the amplitude of the nucleon charge-exchange process at zero angle and the amplitude of the elastic scattering of the neutron on the proton in the “backward” direction, has been considered. Due to the optical theorem, the spin-independent part of the differential cross section of the process n + p → p + n at zero angle for unpolarized particles is expressed through the difference of total cross sections of unpolarized proton-proton and neutron-proton scattering. Meantime, the spin-dependent part of this cross section is proportional to the differential cross section of the deuteron charge-exchange breakup d + p → (pp) + n at zero angle at the deuteron momentum k _d = 2 k _n (k _n is the initial neutron momentum). Analysis shows that, assuming the real part of the spin-independent term of the “forward” amplitude of the process n + p → p + n to be smaller or of the same order as compared with the imaginary part, in the wide range of neutron laboratory momenta k _n > 700 MeV/c the main contribution into the differential cross section of the process n + p → p + n at zero angle is provided namely by the spin-dependent term.     

Quasielastic electron scattering in the giant-resonance energy region

A new method is proposed for extracting the quasielastic portion of the spectrum of scattered electrons. The method is based on the so-called “bin” technique within which a multipole analysis is followed by a determination of the resonance shape and magnitude. The method essentially consists in performing a simultaneous multipole analysis of the mixture of quasielastic and resonance cross sections. A subsequent identification of resonance peaks in the cross section and its quasielastic portion is performed in the energy dependence of the transition probability for each multipolarity, since, there, the difference between the resonance and quasielastic processes is more pronounced than in the spectra of scattered electrons. The method makes it possible to reconstruct the process and to find the energy dependence of the quasielastic cross section in the primary spectra of scattered electrons. The spectra of quasielastically scattered electrons are obtained by the method in question for the ⁶⁵Cu nucleus. The positions of the quasielastic-peak maxima and their shift with respect to the case of scattering on a free nucleon are determined in the momentum-transfer range q = 0.5–1.2 fm^?1.     

Excitation of states of medium-mass nuclei in the region of giant resonances in inelastic deuteron scattering

Results are presented that were obtained by measuring a continuum in the inelastic scattering of 37-MeV deuterons on ¹²C, ⁴⁸Ti, and ^58,64Ni nuclei in the angular range 16° ≤ θ ≤ 61°. Broad excitation maxima are found for deuteron scattering angles in the range θ ≤ 21°. The region of a broad maximum includes giant resonances of target nuclei, whose levels are excited quite readily at E _d = 37 MeV. Summation of the inelastic-scattering cross sections over all final states of the excited| nucleus and the use of completeness of the wave functions for these states make it possible to express the total cross section for inelastic (incoherent) deuteron scattering only in terms of the wave functions for the ground state of the target nucleus. The corresponding quasielastic-scattering amplitude is taken in the diffraction approximation. Nucleon correlations in the target nucleus are disregarded. Upon disregarding a small contribution of multiple quasielastic scattering at small scattering angles, the cross section for incoherent deuteron scattering is represented approximately as the product of known factors—the square of the absolute value of the amplitude for diffractive quasielastic scattering and the effective number of target nucleons scattering deuterons. The results of these calculations agree qualitatively with experimental data.     

Oscillatory screening and quantum interference effects on electron collisions in quantum plasmas

The oscillatory screening and collision-induced quantum interference effects on electron-electron collisions are investigated in dense quantum plasmas. The modified Debye-Hückel potential with the total spin states of the system is considered to obtain the differential electron-electron scattering cross section in quantum plasmas. It is shown that the electron-electron scattering cross section decreases with an increase of the quantum wave number. In addition, the minimum position of the cross section has been appeared with increasing the collision energy at the scattering angle θL=π/4. It is also found that the oscillatory screening effects strongly suppress the cross section near θL=π/4. In addition, it is found that the quantum interference effects suppress the cross section, especially, for the forward and backward scattering cases.     

Spin liquid in an almost ferromagnetic Kondo lattice

A theory of stabilization of a spin liquid in a Kondo lattice at temperatures close to the temperature of antiferromagnetic instability has been developed. Kondo exchange scattering of conduction electrons leads to emergence of a state of the spin liquid of the resonating valence bonds (RVB) type at T>T _K. Owing to this stabilization, low-energy processes of Kondo scattering with energies below T _K are frozen so that the “singlet” state of the Kondo lattice is not realized; instead a strongly correlated spin liquid with developed antiferromagnetic fluctuations occurs. A new version of the Feynman diagram technique has been developed to describe interaction between spin fluctuations and resonant valence bonds in a self-consistent manner. Emergence of a strongly anisotropic RVB spin liquid is discussed. Zh. éksp. Teor. Fiz. 112, 729–759 (August 1997)     

Monte Carlo simulation of elastic and quasielastic nucleus-nucleus scattering

The amplitude of elastic nucleus-nucleus scattering is calculated in framework of the multiple scattering theory. We consider the dependence of the amplitude on slope and cross section ofNN scattering, and on nuclear matter density. The results are compared to approximate calculations. The total inelastic nucleus-nucleus cross sections as well as the cross sections of quasielastic processes are calculated. Predictions are given for the case of superhigh energies.     

The Spin Interaction of a Dirac Particle in an Aharonov-Bohm Potential in First Order Scattering

For a Dirac particle in an Aharonov-Bohm (AB) potential, it is shown that the spin interaction (SI) operator which governs the transitions in the spin sector of the first order S-matrix is related to one of the generators of rotation in the spin space of the particle. This operator, which is given by the projection of the spin operator Σ along the direction of the total momentum of the system, and the two operators constructed from the projections of the Σ operator along the momentum transfer and the z-directions close the SU(2) algebra. It is suggested, then, that these two directions of the total momentum and the momentum transfer form some sort of natural intrinsic directions in terms of which the spin dynamics of the scattering process at first order can be formulated conveniently. A formulation and an interpretation of the conservation of helicity at first order using the spin projection operators along these directions is presented.     

Polarisationsmessungen an Elektronenstrahlen nach der Transmission durch magnetisierte Eisenschichten

Magnetized iron foils of a thickness of 500 Å were transmitted by 60 keV electrons. The spin polarization of the electron beam was investigated by Mott scattering after transmission. No polarization effect was found. Since the lowest detectable polarization degree wasP=0·003 the atomic polarization cross section must be assumed to be smaller than 0·8·10^?20cm². This cross section is the sum of the spin exchange cross section and the spin dependent part of the total scattering cross section. If the electron binding energy is neglected, the spin depentend part of the total scattering cross section can be calculated from the theory of Møller scattering. In the case of our conditions-60 keV and an aperture of 10^?3 radian-the calculated cross section is smaller than the experimental upper limit. In further experiments the electron beam was split into the energy spectrum by an electrostatic analyzer placed between the iron foil and the Mott scattering foil. In these measurements only small parts of the energy spectrum were investigated, however, even here no detectable polarization occured.     

Magnetic field dependence of spin-flip cross section for polarized neutron scattering of CeCu2Si2

The magnetic field dependence of the spin-flip cross section for quasielastic polarized neutron scattering is investigated for the Ce Kondo system at zero temperature. An exact calculation is done for the differential cross section with a small energy transfer and also for the total cross section. In particular the latter case is discussed in detail in order to investigate the recent experiment done for the polycrystalline CeCu₂Si₂. With the use of the obtained results, two possibilities are discussed about the wavefunction for the crystal-field ground doublet of the f-electron in CeCu₂Si₂.     

Identification of biphonons from prominent features of the angular and energy dependences of the inelastic-scattering cross section of biphonon-splitting neutrons

The dispersion relations and wave functions of biphonon and dissociated two-phonon states of anharmonic crystals are used to determine the cross section of inelastic scattering of neutrons that split biphonons into unbound phonons, which scatter each other as a result of their anharmonicity. Prominent features are found of the angular and energy dependences of the cross section, useful for analyzing experimental data to identify biphonons; it is possible that these features can also be used for subsequent, potentially major modification of the system of existing criteria, based solely on energy-balance considerations for the classification of series of spectral resonances, supposedly corresponding to bound multiphonon states of various multiplicities. For a fixed, large loss of neutron energy, the cross section is a maximum in a “nonhead-on” neutron-biphonon collision with a lobe-shaped angular scattering diagram; for intermediate energy losses the cross section has the largest of all possible values at all collision angles; and, for small energy losses, the cross section is a maximum for “head-on” collision in a narrow range of angles. For a fixed angle the energy dependence of the cross section has a resonance peak, which exists at the low-energy edge of a finite energy band for large angles and, as the angle decreases, gradually increases as it shifts toward the high-energy edge of the band, which becomes narrower and shifts into the low-energy region. However, when the angle decreases below a critical value, the still-increasing resonance maximum changes direction and shifts back toward the low-energy edge. It is shown that, despite strong oscillations of the biphonon wave function in the presence of negative phonon dispersion, the cross section does not depend on the sign of the dispersion, i.e., the universal law of independence from this sign, established previously for the dispersion relation and the biphonon damping constant, appears to carry over to the cross section. Fiz. Tverd. Tela (St. Petersburg) 40, 728–734 (April 1998)     

Knockout of charged <Emphasis Type="Italic">ρ</Emphasis> mesons from a nucleon by high-energy electrons in the quasielastic-kinematics region with the participation of transverse virtual photons

The electroproduction of charged ρ mesons on a nucleon under conditions of quasielastic kinematics (Q ² = 2−3 (GeV/c)², W = 2 GeV) is considered. Dominant diagrams are taken into account. It is shown that the transverse cross section for ρ-meson knockout, in just the same was as the respective longitudinal cross section, is dominated by the t-pole diagram involving a virtual ρ meson. This means that the leading contribution to the process comes from direct ρ-meson knockout.     

Elastic and charge exchange scattering of pions on3He in the (3,3)-resonance region

The elastic scattering of pions from³He and the single charge exchange reaction³He(π ^?,π ⁰)³H are calculated in the energy domain of the (3,3)-resonance within the framework of Glauber's theory, including spin and isospin degrees of freedom in all orders. It is pointed out that, from the first minimum on, the differential cross section strongly depends on the parametrization of theπN amplitude, especially on its continuation into the unphysical region of momentum transfer. Single and double spin flip contributions prove to be very important in the charge exchange reaction. Within a modified version of Glauber's formalism, directly usingπN phase shifts rather than amplitudes, the³He charge exchange scattering is reexamined. Whereas the shape of the angle-integrated cross section as a function of pion energy is confirmed, the magnitude is still uncertain within a factor of 2.     

Thermal neutron scattering from a hydrogen-metal system in terms of a general multi-sublattice jump diffusion model—I: Theory

A Multi-Sublattice Jump Diffusion Model (MSJD) for hydrogen diffusion through interstitial-site lattices is presented. The MSJD approach may, in principle, be considered as an extension of the Rowe et al.[1] model. Jump diffusion to any neighbours with different jump times which may be asymmetric in space is discussed. On the basis of the model a new method of calculating the diffusion tensor is advanced. The quasielastic, double differential cross section for thermal neutron scattering is obtained in terms of the MSJD model. The model can be used for systems in which interstitial jump diffusion of impurity particles occurs. In Part II the theoretical results are compared with those for quasielastic neutron scattering from the αNbH_x system.     

A semirelativistic calculation of the deuteron electrodisintegration at the quasielastic peak

The cross section for inelastic electron deuteron scattering at the quasielastic peak is calculated in the laboratory system, using complete relativistic kinematics. The difference between the exact cross section formula andDurand's simple sum rule expression is found to be approximately 1.2% for 4-momentum transfers of 2.5 to 4f^?1 and the influence of the deuteron wave function on the final results to be smaller than 1% for reasonable deuteron models. Final state corrections are introduced through a simple correction term in the cross section formula.