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Register a new userConventional nuclear effects on generalized parton distributions of trinucleons
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S. Scopetta
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The measurement of nuclear Generalized Parton Distributions (GPDs) will represent a valuable tool to understand the structure of bound nucleons in the nuclear medium, as well as the role of non-nucleonic degrees of freedom in the phenomenology of hard scattering off nuclei. By using a realistic microscopic approach for the evaluation of GPDs of 3He, it will be shown that conventional nuclear effects, such as isospin and binding ones, or the uncertainty related to the use of a given nucleon-nucleon potential, are rather bigger than in the forward case. These findings suggest that, if great attention is not paid to infer the properties of nuclear GPDs from those of nuclear parton distributions, conventional nuclear effects can be easily mistaken for exotic ones. It is stressed therefore that 3He, for which the best realistic calculations are possible, represents a unique target to discriminate between conventional and exotic effects. The complementary information which could be obtained by using a 3H target is also addressed.
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The measurement of nuclear Generalized Parton Distributions (GPDs) represents a valuable tool to understand the structure of bound nucleons and the phenomenology of hard scattering off nuclei. By using a realistic, non-relativistic microscopic approach for the evaluation of GPDs of 3He, it will be shown that conventional nuclear effects, such as isospin and binding ones, or the uncertainty related to the use of a given nucleon-nucleon potential, are bigger than in the forward case so that, if great attention is not paid, conventional nuclear effects can be easily mistaken for exotic ones. It is stressed that 3He, for which the best realistic calculations are possible, represents a unique target to discriminate between conventional and exotic effects. The complementary information which could be obtained by using a 3H target, the possible extraction of the neutron information, as well as the relevance of a relativistic treatment, will be also addressed.
The generalized parton distribution H and E of the 3He nucleus, which could be measured in hard exclusive processes, such as coherent deeply virtual Compton scattering, are thoroughly analyzed in impulse approximation, within the Av18 interaction. It is found that their sum is dominated to a large extent by the neutron contribution: The peculiar spin structure of 3He makes this target unique for the extraction of the neutron information. This observation could allow to access for the first time, in dedicated experiments, the orbital angular momentum of the partons in the neutron.
An impulse approximation analysis is described of the generalized parton distributions (GPDs) H and E of the 3He 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 3He, at low momentum transfer, is largely dominated by the neutron contribution, thanks to the unique spin structure of 3He. 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 3He 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.
We derive one-loop matching relations for the Ioffe-time distributions related to the pion distribution amplitude (DA) and generalized parton distributions (GPDs). They are obtained from a universal expression for the one-loop correction in an operator form, and will be used in the ongoing lattice calculations of the pion DA and GPDs based on the parton pseudo-distributions approach.
We present a comprehensive study of the lowest moments of nucleon generalized parton distributions in N_f=2+1 lattice QCD using domain wall valence quarks and improved staggered sea quarks. Our investigation includes helicity dependent and independent generalized parton distributions for pion masses as low as 350 MeV and volumes as large as (3.5 fm)^3, for a lattice spacing of 0.124 fm. We use perturbative renormalization at one-loop level with an improvement based on the non-perturbative renormalization factor for the axial vector current, and only connected diagrams are included in the isosinglet channel.
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