Nuclear medium modifications of hadrons from generalized parton distributions

Abstract

We study the structure of generalized parton distributions (GPDs) in spin 0 nuclei within a microscopic approach for nuclear dynamics. GPDs can be used on one side as tools to unravel the deep inelastic transverse structure of nuclei in terms of both transverse spatial and transverse momentum degrees of freedom. On the other, one can obtain information on GPDs themselves by observing how they become modified in the nuclear environment. We derive the structure of the nuclear deeply virtual Compton scattering tensor and generalized parton distributions at leading order in Q in a field-theoretical framework. The nuclear generalized parton distributions are calculated using a two-step process-the convolution approach-where the scattering process happens from a quark inside a nucleon, itself inside a nucleus, disregarding final state interactions with both the nuclear and nucleon debris. We point out that details of the nuclear long-range interactions, such as two-body currents, can be disregarded compared to the deep inelastic induced modifications of the bound GPDs. We show how the pattern of nuclear modifications predicted, and in particular the deviations of off-shell effects from the longitudinal convolution provide clear signals to be sought in experimental measurements. Finally, we find interesting relationships by studying Mellin moments in nuclei: in particular we predict the A dependence for the D term of GPDs within a microscopic approach and the behavior with t of the total momentum carried by quarks in a nucleus. The latter provides an important element for the evaluation of nuclear hadronization phenomena that are vital for interpreting current and future data at RHIC, HERMES, and Jefferson Lab.

Angular momentum sum rule for spin-one hadronic systems

“…− E]/p, M being the nucleon mass and E the deuteron's binding energy, consistently with the formalism for describing deep inelastic processes from nuclear targets [19] in the approximation where the quarks' k ⊥ dependence is trivially integrated over, and no offshell effects are considered [15]. Our results are shown in Figures 1 and 2.…”

“…H 2 can be explicitly evaluated from Eq. (14) using the convolution formalism that was developed in [15], taking care of the angular structure for the deuteron [16]. For H 2 (x, 0, 0) = H 2 , only the {Λ , Λ} ≡ {1, 1}, {0, 1} deuteron helicity components contribute [13,16],…”

Extracting generalized neutron parton distributions from3He data

“…We note however that careful analyses of these effects for different targets, performed, e.g., in Ref. [14] for 4 He, show that they grow with ∆ 2 , being minimal close to the forward limit, where we are proposing the relevant measurement.…”

“…[11], and for spin zero nuclei in Ref. [12]; a possible link of nuclear GPDs measurements to color transparency phenomena has been presented in Ref. [13].…”

“…Off-shell effects have been studied in Ref. [14] and different medium modifications of nucleon GPDs have been illustrated in Ref. [15].…”