Generalized Parton Distributions in the Deuteron

Abstract

Abstract. We introduce generalized quark and gluon distributions in the deuteron, which can be measured in exclusive processes like deeply virtual Compton scattering and meson electroproduction. We discuss the basic properties of these distributions, and point out how they probe the interplay of nucleon and parton degrees of freedom in the deuteron wave function.Introduction. The partonic structure of the deuteron has been explored in terms of the parton distributions accessible in deep inelastic scattering [1], and in terms of the form factors measured in elastic lepton-deuteron processes [2,3]. It is natural to ask what can be learned from generalized parton distributions (GPDs), introduced not long ago in [4,5]. For the nucleon case it has been shown that these quantities contain unique information about the dynamics of quarks and gluons in QCD bound states, beyond what can be unraveled from ordinary parton distributions and form factors. Here we extend these studies to the case of the deuteron, with the aim of providing the theoretical framework to analyze and interpret present and future measurements with deuteron targets. We restrict ourselves to parton distributions of twist two, and to the parton helicity conserving sector, which is relevant in most phenomenological applications. Quark and gluon helicity flip GPDs can be treated with the same methods.

Angular momentum sum rule for spin-one hadronic systems

“…H q 2 (x, ξ, t)'s first moment is equal to the deuteron magnetic form factor G 2 (t) ≡ G M (t) [9]. This expression can be compared to the nucleon sum rule [3],…”

“…For a spin one system one can write this in terms of five unpolarized GPDs (from the Lorentz symmetric part of the hadronic tensor) [9],…”

Generalized Parton Distributions – theoretical review –

“…The latter is induced by the renormalization prescription of the operators, which is part of the GPD definition. To deal with the polarization of the hadronic states, one might introduces a form factor decomposition [ 6,10]. For instance, for the nucleon GPD Dirac and Pauli-like form factors appear in the vector case [ 6]:…”

“…Another class of hard exclusive processes, in which GPDs are accessible, are those in which the struck parton is purely probed within the electromagnetic interaction via the absorbtion and emission of photons [ 1]: photo leptoproduction [ 47,26], see Fig. 3, lepton pair photoproduction [ 48] and lepton pair leptoproduction [ 49]. In the first two processes the photon virtuality is space-and time-like respectively, while in the third one both photons are virtual.…”

“…This opens a new window for the study of nucleus binding effects, especially, for the deuteron [ 10,52].…”