Relativistic one-boson-exchange model and elastic electron-deuteron scattering at high momentum transfer

Abstract

A relativistic covariant analysis of the elastic electromagnetic form factors of the deuteron is carried out using the one-boson-exchange model, including the pny and coey mesonic-exchange-current contributions. The theoretical predictions are compared with the recent experimental data at high momentum transfer.PACS numbers: 25.30.Bf, 24.10.-i, 25.10,+s, 27.10.+h Experimental data 1 " 3 have recently become available on the elastic electromagnetic (em) form factors of the deuteron at high momentum transfer, which may help in discriminating between the predictions of various dynamical theories of the nuclear interaction. In particular, they can serve as a testing ground for the limits of validity of the conventional meson description in this region. In this picture, mesonic exchange currents (MEC's) are shown to play an important role in elastic electron scattering on nuclei. 4 The so-called pair term, being of relativistic origin, and true MEC graphs like the pny and coey graphs yield important contributions at intermediate momentum transfer. 5 " 7 However, for the pair term it has been argued in the case of the deuteron using a relativistic one-boson-exchange (OBE) model 8 that a consistent relativistic treatment of both the nucleon-nucleon dynamics and the em interaction is needed. 9 In particular, the pair term contribution to the magnetic deuteron form factor is grossly canceled by a correction from the nucleon-nucleon dynamics, 9 resulting in a disparity with the experimental data at moderately large momentum transfer. 2 Usually the MEC graphs are calculated in a nonrela-| tivistic framework. Moreover, only leading orders in the kinetic motion of the nucleons and momentum transfer are kept in the calculation of the effective two-body em operators. 6 At high momentum transfer these approximations are certainly not expected to be reliable anymore. In this Letter we present results of a fully relativistic analysis of the MEC contributions to the em form factors using the OBE model. The model was studied previously 10 in the relativistic impulse approximation (IA). The calculation we report on has clearly the virtue that both the nucleonic and mesonic contributions to the em current are carried out within the same dynamical model. As noted previously, at the level of the IA, the pair term is already automatically included in this formalism, since it is done in a fully relativistic covariant way. Relativistic calculations of the MEC contributions are done starting from the deuteron current matrix elements in the Breit frame. From these the em form factors can immediately be deduced. For a detailed description of this formalism we refer to Ref. 10. Denoting the relative momenta of the final and initial states as p' and />, we have {P\M^J^\PM)---\z^(1) 2M d (2n)where <E>^A f) represents the deuteron vertex function with total four-momentum P and polarization M. Furthermore, S2(p,P) is the free two-nucleon Green's function and T^ describes the em vertex. The deuteron vertex function oi M) is calculated in the two-nu...

Elastice−dscattering data and the deuteron wave function

“…This fact was first demonstrated by Hummel and Tjon [15] in the context of relativistic boson-exchange-model calculations of the deuteron form factors, based on the Blankenbecler-Sugar reduction of the Bethe-Salpeter equation. It was later confirmed, in a calculation of the deuteron B(q) structure function [2], that next-to-leading-order terms in the expansion for j ρπγ , proportional (1 + κ ρN N )/m 2 , very substantially reduce the contribution of the leading term.…”

Sensitivity of pp-bremsstrahlung to meson-exchange currents

“…We add to this the perturbative ρπγ, ωπγ, ρηγ, ωηγ and N∆γ(π, ρ) exchange currents currents shown in Fig 1(d-e), all of which are easily calculated in the usual way [20][21][22][23] with,…”

Electron Scattering from Tensor-Polarized Deuterons in the VEPP-3 Electron Storage Ring

“…The number of events in each bin was normalized by the collected charge, and the resulting scattering yields were reduced to an experimental asymmetry defined as: Gem = s 2+ sl. (6) in which S l k is the sum of the counting rates in the detector systems facing the directions ±ni, with the magnetic guide field pointing in direction TLJ, and the sign of p zz given by k. The values of a exp so obtained are listed in table 1.…”