Relativistic effects in proton-induced deuteron break-up at intermediate energies with forward emission of a fast proton pair

Recent data of the reaction with a fast forward pp pair with small excitation energy is analyzed within a covariant approach based on the Bethe-Salpeter formalism. Relativistic effects in cross-section are extracted and found to be large. It is demonstrated that the node of the non-relativistic amplitude is shifted and masked by relativistic effects from Lorentz boost and the negative-energy P components in the ¹S₀ Bethe-Salpeter amplitude of the pp pair.Received: 22 July 2003, Revised: 7 October 2003, Published online: 5 February 2004PACS: 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 25.10. + s Nuclear reactions involving few-nucleon systemsL.P. Kaptari: On leave of absence from Bogoliubov Laboratory of Theoretical Physics, JINR, Dubna, Russia; also at Department of Physics, Universitá di Perugia, and INFN Sezione di Perugia, via A. Pascoli, I-06100, Italy.Present address S.S. Semikh: Bogoliubov Laboratory of Theoretical Physics, JINR, Dubna, Russia.     

Longitudinal Structure Function FL at Small x Extracted from the Berger–Block–Tan Parametrization of F2

JETP Letters - The longitudinal structure function FL(x, Q2) is extracted at low values of the Bjorken variable x from the Berger-Block-Tan parametrization of F2(x, Q2). The obtained structure...     

Charge-exchange reaction pd → n(pp) within the Bethe-Salpeter approach

The charge-exchange reaction pd → n(pp) at low momentum transfers and low excitation energies of the pp pair is considered within the Bethe-Salpeter approach. The method is proposed for calculating observables in the case where the pp pair is in the ¹ S ₀ state. The results of methodological numerical calculations for the differential cross sections and the tensor analyzing power T ₂₀ are presented. The possibility of using the reaction in question as a basic reaction for creating a deuteron tensor polarimeter at high energies and for obtaining additional information about the elementary amplitude for nucleon-nucleon charge-exchange is predicted.     

Short Range Correlations and Wave Function Factorization in Light and Finite Nuclei

Recent BNL and Jlab data provided new evidence on two nucleon correlations (2NC) in nuclei. The data confirm the validity of the convolution model, describing the spectral function (SF) of a correlated pair moving in the mean field with high and low relative and center-of-mass (cm) momenta, respectively. The model is built assuming that the wave function (WF) of a nucleus A, describing a configuration where the cm momentum of a correlated pair is low and its relative momentum is high, factorizes into the product of the two-body WF and that of the A-2 system. Such a factorization has been shown to occur in nuclear matter (NM). Here it is shown that few-body systems exhibit factorization, which seems to be therefore a general property, to be reproduced also in studies of the WF of finite nuclei.     

Pion-Exchange Effects in Elastic Backward Proton-Deuteron Scattering

 The elastic backward proton-deuteron scattering is analyzed within a covariant approach based on the deuteron vertex function obtained by the Bethe-Salpeter equation with realistic meson-exchange interaction. Contributions of the one-nucleon and one-pion exchange mechanisms to the cross section and polarization observables are investigated in explicit form. Results of numerical calculations for the cross section, tensor analyzing power and spin transfers are presented. The one-pion exchange contribution is essential for describing the spin-averaged cross section, while in polarization observables it is found to have a small effect. Received December 22, 1998; revised November 8, 1999; accepted November 10, 1999     

Di-electrons from η -meson Dalitz decay in proton-proton collisions

The reaction is discussed within a covariant effective meson-nucleon theory. The model is adjusted to data of the subreaction . Our focus is on di-electrons from Dalitz decays of η -mesons, , and the role of the corresponding transition form factor . Numerical results are presented for the intermediate-energy kinematics of HADES experiments.     

Solving the Bethe–Salpeter Equation in Euclidean Space

Different approaches to solve the spinor–spinor Bethe–Salpeter (BS) equation in Euclidean space are considered. It is argued that the complete set of Dirac matrices is the most appropriate basis to define the partial amplitudes and to solve numerically the resulting system of equations with realistic interaction kernels. Other representations can be obtained by performing proper unitary transformations. A generalization of the iteration method for finding the energy spectrum of the BS equation is discussed and examples of concrete calculations are presented. Comparison of relativistic calculations with available experimental data and with corresponding non relativistic results together with an analysis of the role of Lorentz boost effects and relativistic corrections are presented. A novel method related to the use of hyperspherical harmonics is considered for a representation of the vertex functions suitable for numerical calculations.