Neutron orbital structure from generalized parton distributions of 3 He

2014

EPJ Web of Conferences

Abstract. It has been recently proposed to study coherent deeply virtual Compton scattering (DVCS) off 3 He nuclei to access neutron generalized parton distributions (GPDs). In particular, it has been shown that, in Impulse Approximation (IA) and at low momentum transfer, the sum of the quark helicity conserving GPDs of 3 He, H and E, is dominated by the neutron contribution. This peculiar result makes the 3 He target very promising to access the neutron information. We present here the IA calculation of the spin dependent GPDH of 3 He. Also for this quantity the neutron contribution is found to be the dominant one, at low momentum transfer. The known forward limit of the IA calculation ofH , yielding the polarized parton distributions of 3 He, is correctly recovered. The extraction of the neutron information could be anyway non trivial, so that a procedure, able to take into account the nuclear effects encoded in the IA analysis, is proposed. These calculations, essential for the evaluation of the coherent DVCS cross section asymmetries, which depend on the GPDs H , E andH , represent a crucial step for planning possible experiments at Jefferson Lab.Generalized parton distributions (GPDs), introduced in Ref.[1], describe the hadron non perturbative structure in hard exclusive processes. The study of these quantities is very important to understand several open issues of hadrons, such as, e.g., their spin structure. GPDs are related to the total angular momentum of partons inside the hadron; their knowledge, once the helicity quark contribution were subtracted, would make possible to access their orbital angular momentum (OAM) content.The most promising process for these studies is likely deeply virtual compton scattering (DVCS), i.e., the reaction eH −→ e H when Q 2 M 2 (Q 2 = −q · q is the momentum transfer between the leptons e and e , 2 the one between hadrons H and H with momenta P and P , and M the nucleon mass). Another relevant kinematical variable is the so called skewedness, = − + /(P + + P + ) 1 .

Section: Epj Web Of Conferencesmentioning

confidence: 92%

“…The treatment has been later extended toG 3,q M (see Ref. [8] for details), and toH 3 q , giving the following result:…”

Section: Epj Web Of Conferencesmentioning

confidence: 99%

See 1 more Smart Citation

Coherent deeply virtual Compton scattering off³He and neutron generalized parton distributions

2014

EPJ Web of Conferences

“…In Ref. [19] it has been found that the sum of the GPDs H 3 q and E 3 q , at low momentum transfer, is indeed dominated to a large extent by the neutron contribution, making 3 He targets very promising for the extraction of the neutron information. However, this is not the end of the story.…”

Section: Introductionmentioning

confidence: 99%

“…In the next section, part of the formalism used in the IA analysis, only sketched in the previous Rapid Communication, Ref. [19], is developed and motivated. In the third one, the ingredients used in the calculation are described.…”

Section: Introductionmentioning

confidence: 99%

Extracting generalized neutron parton distributions from3He data

2013

Phys. Rev. C

Self Cite

An impulse approximation (IA) analysis is described of the generalized parton distributions (GPDs) H and E of the 3 He nucleus, quantities which are accessible in hard exclusive processes, such as coherent deeply virtual Compton scattering (DVCS). The calculation is based on the Av18 interaction. The electromagnetic form factors are correctly recovered in the proper limits. The sum of the GPDs H and E of 3 He, at low momentum transfer, is largely dominated by the neutron contribution, thanks to the unique spin structure of 3 He. This nucleus is therefore very promising for the extraction of the neutron information. By increasing the momentum transfer, however, this conclusion is somehow hindered by the the fast growing proton contribution. Besides, even when the neutron contribution to the GPDs of 3 He is largely dominating, the procedure of extracting the neutron GPDs from it could be, in principle, nontrivial. A technique is therefore proposed, independent on both the nuclear potential and the nucleon model used in the calculation, able to take into account the nuclear effects included in the IA analysis and to safely extract the neutron information at values of the momentum transfer large enough to allow the measurements. Thanks to this observation, coherent DVCS should be considered a key experiment to access the neutron GPDs and, in turn, the orbital angular momentum of the partons in the neutron.

Generalized Parton Distributions of 3He and the Neutron Orbital Structure

2013

Few-Body Syst

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The two leading twist, quark helicity conserving generalized parton distributions (GPDs) of 3 He, accessible, for example, in coherent deeply virtual Compton scattering (DVCS), are calculated in impulse approximation (IA). Their sum, at low momentum transfer, is found to be largely dominated by the neutron contribution, so that 3 He is very promising for the extraction of the neutron information. Anyway, such an extraction could be not trivial. A technique, able to take into account the nuclear effects included in the IA analysis in the extraction procedure, even at moderate values of the momentum transfer, is proposed. Coherent DVCS arises therefore as a crucial experiment to access, for the first time, the neutron GPDs and the orbital angular momentum of the partons in the neutron. Keywords Three body systems · Generalized parton distributionsGeneralized Parton Distributions (GPDs) [1] parameterize the non-perturbative hadron structure in hard exclusive processes, allowing to access unique information such as, for example, the parton total angular momentum [2]. By subtracting from the latter the helicity quark contribution, measured in other hard processes, the parton orbital angular momentum (OAM), contributing to the nucleon spin, could be then estimated, a crucial step towards the solution of the so called "Spin Crisis".The cleanest process to access GPDs is Deeply Virtual Compton Scattering (DVCS), i.e. eH −→ e ′ H ′ γ when Q 2 ≫ M 2 (Q 2 = −q · q is the momentum transfer between the leptons e and e ′ , ∆ 2 the one between hadrons H and H ′ with momenta P and P ′ , and M is the nucleon mass. Another relevant kinematical variable is the so called skewedness, ξ = −∆ + /(P + + P ′ + ) 1 ). Despite severe difficulties to extract GPDs from experiments, data for proton and nuclear targets are being analyzed, see, i.e., Refs. [3,4]. The measurement of GPDs for nuclei could be crucial to distinguish between different models of nuclear medium 1 In this paper, a ± = (a 0 ± a 3 )/ √ 2