N. P. Yudin

Two-body forces and the giant resonance in photo-nuclear reactions

Abstract Partial cross sections as well as energy and angular distributions of photodisintegration products of the Ca40 nucleus are calculated using the shell model. It is shown that the use of empirical data on the levels of the adjacent nuclei and the account of nucleon-nucleon interactions make it possible to describe satisfactorily the photodisintegration of the giant resonance region.

Measurement of the tensor analyzing power Ayy in inclusive breakup of 9 GeV/c deuterons on carbon at large transverse momenta of protons

Abstract The tensor analyzing power A yy in inclusive breakup of 9 GeV/c deuterons on carbon has been measured at the detected proton angle of 85 mr. The analyzing power remains positive at the highest measured momentum of the proton in definite contradiction with the predictions of the existing models. The vector analyzing power A y has been obtained simultaneously with A yy .

On the structure of giant dipole resonance in 32S

Abstract The photodisintegration of the 32 S nucleus is calculated in the framework of the microscopical model. The spread of the Fermi surface as well as particle and hole coupling with low-lying states are taken into account. The general features of the calculated absorption spectrum and different photonuclear reactions are discussed. An attempt is made to determine the origin of the peaks in the absorption spectrum on the basis of some reactions and calculated Coulomb form factors. Satisfactory agreement with experimental data is obtained.

Fragmentation of 9 GeV/c deuterons in the region of proton transverse-momenta of 0.5-1 GeV/c and the deuteron wave-function at small distances

Abstract Momentum spectra of protons emitted at angles of 0.103, 0.139 and 0.157 rad in fragmentation of 9 GeV/ c deuterons on 1 H, 2 H and 12 C nuclei have been measured at the JINR synchrophasotron by using a magnetic spectrometer. It is found that the shape of the high-momentum parts of the spectra is defined only by the deuteron structure and the mechanism of deuteron-nucleon interaction and does not depend on a target. The contributions to the differential cross section of the 1 H(d, p)X reaction have been determined, which are conditioned by elastic and inelastic scatterings of deuteron nucleons on a proton, stripping, their interference, and also the excitation of the pion degrees of freedom. In the framework of the light front dynamics, calculations of the proton spectra with the deuteron structure functions for the Paris, Reid soft core, and Bonn potentials have been performed; a better agreement with the experiment is achieved with the deuteron wave function for the Paris potential. A conclusion is made that the nucleons in a deuteron keep their individuality up to relative motion momenta of ∼ 1 GeV/ c .

Possible interpretation of the „anomalous“ behaviour of the proton spectrum at 0° from the deuteron fragmentation at 9 GeV/c

The momentum spectra of protons, produced at 0° as a result of fragmentation of relativistic deuterons on nuclei, are analyzed. Possible causes of the existing discrepancy of the data on the 0° proton spectrum from the1H(d,p)X reaction at 9.1 GeV/c with results of the impulse approximation calculations are considered. It is shown that taking into account the finite angular resolution of the experimental setup and the corresponding renormalization of the experimental data, on the one hand, and also the inclusion of the additional (to stripping) contribution of protons from the scattering of deuteron nucleons by target protons, on the other, make it possible to match these data with the results of calculations within the framework of the relativistic impulse approximation using the deuteron wave function for the Paris potential.

Measurement of the tensor Ayy and vector Ay analyzing powers of the deuteron inelastic scattering of beryllium at 5.0 GeV/c and 178 mrad

Tensor Ayy and vector Ay analyzing powers in the inelastic scattering of deuterons with a momentum of 5.0 GeV/c on beryllium at an angle of 178 mrad in the vicinity of the excitation of baryonic resonances with masses up to ∼ 1.8 GeV/c2 have been measured. The Ayy data are in good agreement with the previous data obtained at 4.5 and 5.5 GeV/c. The results of the experiment are compared with the predictions of the plane-wave impulse approximation and ω meson-exchange models.Tensor Ayy and vector Ay analyzing powers in the inelastic scattering of deuterons with the momentum of 5.0 GeV/c on beryllium at an angle of 178 mr in the vicinity of the excitation of baryonic resonances with masses up to 1.8 GeV/c^2 have been measured. The Ayy data are in a good agreement with the previous data obtained at 4.5 and 5.5 GeV/c. The results of the experiment are compared with the predictions of the plane wave impulse approximation and \omega-meson exchange models.

The electroexcitation of 32S in the region of the dipole resonance

Abstract The C1 + E1 and M2 form factors for inelastic scattering of high-energy electrons by 32 S in the region of the dipole giant resonance have been calculated. The used wave functions of excited states were obtained in terms of a microscopic “particle-hole” approach of the shell model taking into account the configurational splitting and coupling of the particle-hole excitations to one- and two-phonon states. A reasonable fit with the experimental data of Afanasyev and coworkers for the 32 S excitation curve at different momentum transfers q ≦ 1 fm ≈1 was obtained though the agreement of theγ-quanta absorption cross sections and the (γ, n) reaction with the experiment is not satisfactory. It is emphasized that the cross sections (γ, γ), (γ, Po) and (p, γo), the photonucleon spectra and the transverse electron scattering form factors are particularly sensitive to the configurational composition of wave functions in different regions of the 32 S excitation curve.

Quark Microscopic Picture for Vector and Pseudoscalar Mesons in the Nucleon and Their Quasielastic Knockout by High-Energy Electrons

A technique for projecting a multiquark wave function in the microscopic model of a 3P0 scalar fluctuation onto the virtual-decay channels N → N + ρ and N → N + π is formulated (at a more general level for the latter than previously). The amplitude for the electromagnetic transition ρ + γT* → π in electron-induced quasielastic rho-meson knockout followed by rho-meson conversion to a pion is considered. Theoretical results obtained in this way are contrasted against available experimental data, and reasonable agreement is found for cross-section values. This confirms a universal character of the 3P0 model. The precision of relevant experiments is as yet insufficient for comparing the momentum distribution of the rho meson from the channel N → N + ρ with its theoretical counterpart.

Angular distributions of electrons in the (γ, 2e) reaction andee-correlations in the atom

The cross sectionsd3σ/dE1dn1dn2 for the Ar (γ, 2e) Ar++ process are calculated on the basis of the diagram approach within the energy intervalω=400–650 eV as functions of the angleθ12 between final electrons with equal energiesE1=E2 for several levels of the final Ar++ ion. It has been elucidated that the interference of amplitudes corresponding to the interaction in the final and initial states is of prime importance. The angular distributions over the angleθ12 are very sensitive to the term of the final ion. There are numerous data for the experimental verification of the theory, in particular, for the selection of leading diagrams. The (e, 3e) experiment is also desirable.

Quasielastic rho-meson knockout from nucleons by high-energy electrons

The electroproduction of charged rho mesons on a nucleon under conditions of quasielastic kinematics [Q2 > 2 (GeV/c)2, W > 3 GeV, and ωρ ≃ q0 in the laboratory frame] is considered. The main diagrams involved in this process are taken into account, and it is shown that the case of rho-meson knockout by a longitudinal photon is dominated by the t-channel pole diagram featuring a rho meson, so that direct rho-meson electroknockout makes a leading contribution to the process being considered. Questions concerning the gauge invariance of the electroproduction process are considered in detail, along with contact terms that inevitably arise in employing form factors in ρNN vertices and which are necessary for restoring gauge invariance. It is shown that the structure of these contact terms is not determined exclusively by the requirement that the electroproduction amplitude be gauge-invariant and may be such that the corresponding correction to the dominant diagram due to these terms proves to be suppressed in the quasielastic region (with increasing Q2), with the result that the t-pole process featuring a rho meson remains dominant; at the same time, the contribution of this correction is significant at low Q2 or in the case of photoproduction, modifying substantially the electroproduction cross section.