M. Traini

Longitudinal and transverse responses in quasi-elastic electron scattering from 208Pb and 4He

Abstract Longitudinal and transverse response functions, R L and R T , have been obtained in inclusive quasi-elastic electron scattering from 4 He and 208 Pb, for momentum transfers between 300 and 650 MeV/ c and energy transfers up to 350 MeV. A quenching of R L , ∼ 14% in 4 He and ∼ 50% in 208 Pb has been observed. Interpretations in terms of correlations and modification of nucleon form factors in the nuclear medium are discussed.

Linking generalized parton distributions to constituent quark models

Abstract The link between the nucleon generalized parton distributions and the non-diagonal one-body density matrix in momentum space is studied. Attention is focused on the region where quark generalized parton distributions (GPDs) describe emission and reabsorption of a single active quark by the target nucleon. The correct covariant connection with wave functions used in any constituent quark model is established. Results obtained with different constituent quark models are presented for the unpolarized quark GPDs.

Constituent quarks and parton distributions

Abstract The high energy parton distribution when evolved to a low energy scale appears to indicate that a valence picture of hadron structure arises. We have developed a formalism based on a laboratory partonic description which connects the parton distributions with the momentum distributions of a quark model. The formalism uses Next to Leading Order evolution and has been defined to produce the right support for the parton distributions. In this scheme we have analyzed the polarized and unpolarized data and shown that well-known Quark Models lead to a qualitative description of the data. However, if one aims at a quantitative agreement, these conventional low energy models have to be changed to include higher momentum and angular momentum components. Moreover, if the present gluon distributions, despite their indirect extraction, are taken to be an accurate description of nature, the need of primordial gluons or constituent quark substructure is an outcome of our calculation.

Nucleon momentum distributions in doubly closed shell nuclei

The momentum distributions in nuclei like4He,16O and40Ca are explicitly calculated within a phenomenological model which includes dynamical short range and tensor correlation effects. The common behaviour of such distributions in the high momentum region, already established in light nuclei, is extended to the medium weight region. Comparison with existing calculations is discussed and, for completeness, also form factors are evaluated within the same framework.

Time-dependent Hartree-Fock polarizability and random phase approximation sum rules: (I). Theory

Abstract The linear response of a nucleus in an external oscillating field has been studied in the framework of TDHF theory. The dynamic polarizability evaluated in TDHF theory has been related to RPA energies and matrix elements and a method to obtain RPA sum rules from the TDHF polarizability has been explicitly developed. This method can be applied to isoscalar as well as to isovector and spin excitations. Finally, a prescription to identify mass and restorting force parameters of various collective models with RPA sum rules is given.

Towards a unified picture of constituent and current quarks

Using a simple picture of the constituent quark as a composite system of point-like partons, we construct the parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We evaluate the latter at a low hadronic scale with updated phenomenological information, and we build the momentum distributions using well-known quark models. The resulting parton distributions and structure functions are evolved to the experimental scale and good agreement with the available DIS data is achieved. When compared with a similar calculation using non-composite constituent quarks, the accord with experiment of the present calculation becomes impressive. We therefore conclude that DIS data are consistent with a low energy scenario dominated by composite, mainly non-relativistic constituents of the nucleon.Abstract Using a simple picture of the constituent quark as a composite system of point-like partons, we construct the parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We evaluate the latter at a low hadronic scale with updated phenomenological information, and we build the momentum distributions using well-known quark models. The resulting parton distributions and structure functions are evolved to the experimental scale and good agreement with the available DIS data is achieved. When compared with a similar calculation using non-composite constituent quarks, the accord with experiment of the present calculation becomes impressive. We therefore conclude that DIS data are consistent with a low energy scenario dominated by composite, mainly non-relativistic constituents of the nucleon.

Deep inelastic parton distributions and the constituent quark model

Abstract The parton distributions of the nucleon are evaluated dynamically under the assumption that at a low-resolution scale the nucleon consists entirely of valence constitutent quarks. Results from various constituent-quark models are presented and the one-gluon-exchange effects, as described by spin-isospin potential approximations, are discussed. The predictions are compared with the experimental observations from deep inelastic muon-nucleon scattering.

Dynamical correlations in finite nuclei: A simple method to study tensor effects

Abstract Dynamical correlations are introduced in finite nuclei by changing the two-body density through a phenomenological method. The role of tensor and short-range correlations in nuclear momentum distribution, electric form factor and two-body density of 4 He is investigated. The importance of induced tensor correlations in the total photonuclear cross section is reinvestigated providing a successful test of the method proposed here.

Double parton correlations and constituent quark models: a light front approach to the valence sector

A bstractAn explicit evaluation of the double parton distribution functions (dPDFs), within a relativistic Light-Front approach to constituent quark models, is presented. dPDFs encode information on the correlations between two partons inside a target and represent the non-perturbative QCD ingredient for the description of double parton scattering in proton-proton collisions, a crucial issue in the search of new Physics at the LHC. Valence dPDFs are evaluated at the low scale of the model and the perturbative scale of the experiments is reached by means of QCD evolution. The present results show that the strong correlation effects present at the scale of the model are still sizable, in the valence region, at the experimental scale. At the low values of x presently studied at the LHC the correlations become less relevant, although they are still important for the spin-dependent contributions to unpolarized proton scattering.

Helicity-dependent generalized parton distributions in constituent quark models

Abstract Helicity-dependent generalized parton distributions of the nucleon are derived from the overlap representation of generalized parton distributions using light-cone wave functions obtained in constituent quark models. Results from two different quark models are used also to study the angular momentum sum rule and the spin asymmetry in polarized electron scattering.