New short-range electromagnetic current in the deuteron
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NUCLEI Theory
New Short-Range Electromagnetic Current in the Deuteron* V. I. Kukulin1), I. T. Obukhovsky1), V. N. Pomerantsev1) , P. Grabmayr2) , and A. Faessler3) Received March 3, 2006; in final form, August 1, 2006
Abstract—A new model for short-range isoscalar current in the deuteron and N N system is developed and tested on a variety of isoscalar magnetic observables such as the deuteron magnetic moment, magnetic form factor, and the circular polarization of photons at np radiative capture at thermal neutron energies. The model for electromagnetic two-nucleon current proposed in the paper is based on generation of an intermediate dibaryon in the short-range N N interaction. This intermediate dibaryon, in turn, is treated within the new model for intermediate and short-range N N interaction recently proposed by the present authors. The transition current model developed here satisfies the current conservation relation by the construction. Our calculations have demonstrated that the new current model, using only one parameter (with a clear physical meaning), is able to describe, in very good agreement with the experimental data, three basic deuteron observables of magnetic type, viz., the magnetic moment, the photon circular polarization in the p(n, γ )d process, and the structure function B(Q2 ) up to Q2 60 fm−2 . PACS numbers : 12.39.Jh, 25.10.+s, 25.20.Lj DOI: 10.1134/S1063778807020020
1. MOTIVATION OF THE WORK Despite the very long and rich prehistory and huge literature of works done to date, the problem of electromagnetic currents in the deuteron can by no means be considered as fully resolved or even well understood. This conclusion remains valid even if one is restricted to very moderate energies or momentum transfer. As good examples, let us point out three typical problems—all related to the low-energy region— where one still cannot reach a quantitative agreement with experimental data even for the best available theoretical approaches, and in spite of the inclusion in the theoretical framework of many tiny effects. These problems are the following: (i) The photon circular polarization Pγ in the radiative capture process n + p → d + γ at thermal energies [1–6]. (ii) Theoretical prediction of the accurate value for the deuteron magnetic moment (which is known experimentally with a very high accuracy). (iii) γ-Induced spin polarization of outgoing neutrons in the photoreaction d(γ, n)p at Eγ = 5−10 MeV [7]. ∗
The text was submitted by the authors in English. Institute of Nuclear Physics, Moscow State University, Moscow, Russia. 2) ¨ Institute of Physics, Tubingen, Germany. 3) ¨ Institute for Theoretical Physics, Tubingen, Germany. 1)
Even the quantitative explanation for the unpolarized n + p → d + γ cross section at very low energies has been reached only in recent years [8, 9]. Many important processes related to the above problems have many common features with these problems, e.g., the bremsstrahlung pp → ppγ process [10], the 3 He(e, e pp) [7, 11, 12] and 3 He(γ, pp) [10] reactions, the neu
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