3He structure from coherent hard exclusive processes

Hard exclusive processes, such as deep electroproduction of photons and mesons off nuclear targets, could give access, in the coherent channel, to nuclear generalized parton distributions (GPDs). Here, a realistic microscopic calculation of the unpolarized quark GPD H_q of the 3He nucleus is reviewed. In Impulse Approximation, H_q is obtained as a convolution between the GPD of the internal nucleon and the non-diagonal spectral function, describing properly Fermi motion and binding effects. The obtained formula has the correct limits. Nuclear effects, evaluated by a modern realistic potential, are found to be larger than in the forward case. In particular, they increase with increasing the momentum transfer and the asymmetry of the process. Another feature of the obtained results is that the nuclear GPD cannot be factorized into a Delta^2-dependent and a Delta^2-independent term, as suggested in prescriptions proposed for finite nuclei. The dependence of the obtained GPDs on different realistic potentials used in the calculation shows that these quantities are sensitive to the details of nuclear structure at short distances.Comment: 8 pages, talk given at the "X Convegno su problemi di fisica nucleare teorica", October 6-9, 2004, Cortona, Italy. To appear in the Proceeding

The effects of nuclear structure on generalized parton distributions of 3He

The effect of the nuclear medium on generalized parton distributions (GPDs) is studied for the 3He nucleus, through a realistic microscopic analysis. In Impulse Approximation, Fermi motion and binding effects, evaluated by modern potentials, are found to be larger than in the forward case and very sensitive to the details of nuclear structure at short distances.Comment: 4 pages, talk given at the Conference "Baryons 2004", October 25-29 2004, Pailaseau (France), to be published by Nuc. Phys.

Parton distributions in a constituent quark scenario

A simple picture of the constituent quark as a composite system of point-like partons is used to construct the unpolarized and polarized parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We achieve good agreement with experiments in the unpolarized, as well as, in the polarized case. When our results are compared with similar calculations using non-composite constituent quarks, the accord with the experiments of the present scheme is impressive. We conclude that DIS data are consistent with a low energy scenario dominated by composite constituents of the nucleon.Comment: 4 pages; latex using espcrc1.sty; 4 postscript figures; Invited talk at the Workshop ``Nucleon '99'', Frascati; Italy 7-9 June 1999. Submitted to Nuc. Phys.

Parton correlations in double parton scattering

Double parton scattering events are directly sensitive to the correlations between two partons inside a proton and can answer fundamental questions on the connections between the proton constituents. In this chapter, the different types of possible correlations, our present knowledge of them, and the processes where they are likely to be important, are introduced and explained. The increasing integrated luminosity at the LHC and the refinements of the theory of double parton scattering, lead to interesting prospects for measuring, or severely constraining, two-parton correlations in the near future.Comment: Prepared for: Multiple Parton Interactions at the LHC, Eds. P. Bartalini and J. R. Gaunt, World Scientific, Singapore; v2: references adde