Flexible Parametrization of Generalized Parton Distributions: The Chiral-Odd Sector

We present a physically motivated parameterization of the chiral-odd generalized parton distributions. The parametrization is an extension of our previous one in the chiral-even sector which was based on the reggeized diquark model. While for chiral even generalized distributions a quantitative fit with uncertainty estimation can be performed using deep inelastic scattering data, nucleon electromagnetic, axial and pseudoscalar form factors measurements, and all available deeply virtual Compton scattering data, the chiral-odd sector is far less constrained. While awaiting the analysis of measurements on pseudoscalar mesons exclusive electroproduction which are key for the extraction of chiral odd GPDs, we worked out a connection between the chiral-even and chiral-odd reduced helicity amplitudes using Parity transformations. The connection works for a class of models including two-components models. This relation allows us to estimate the size of the various chiral odd contributions and it opens the way for future quantitative fits.Comment: 35 pages, 18 figures, text changes, corrected typos, added fig.

Methane-Rare Gas Interaction Potentials from Scattering Experiments

By using total differential cross sections with resolved diffraction oscillations and absolute integral cross sections with glory oscillations, a new improved spherically averaged potential surface for Ne-CH4 is determined with a potential well depth of ε = 5.50 meV and a minimum distance of Rm = 3.78 Å. A slightly improved parameter set is also given for the isotropic Ar-CH4 interaction. By assuming the same realistic reduced potential form as was found for Ne-CH4 and Ar-CH4, the isotropic parts of the potential for Kr-CH4 and Xe-CH4 are obtained from absolute integral cross sections

Generalized parton distributions, the hunt for quark orbital momenta

The Generalized Parton Distributions (GPDs) are the appropriate framework for a universal description of the partonic structure of the nucleon. They characterize the dynamics of quarks and gluons inside the nucleon and consequently contain information about the spin of the nucleon. The current experimental knowledge about GPDs is reviewed with the emphasis on the determination of E^q(Q^2,x,xi,t), the least known and constrained GPD, of particular importance in the nucleon spin puzzle. The perspectives of this experimental program are also addressed.Comment: 6 pages, 2 figures Proceedings of the XVIIIth Symposium on Spin Physics, Charlottesville (Virginia, USA), October 6-11,200

Transverse spin in exclusive experiments

We analyze a number of open questions in the application of the concept of generalized parton distribution to various high-energy exclusive processes. In particular we discuss the feasibility of global fits of the exclusive data, and provide a recursive procedure based on a physically motivated parametrization. By fixing the parameters to the Deeply Virtual Compton Scattering data we make predictions for chiral odd quantities, including transversity. All of our predictions include theoretical error

Generalized parton distributions: Status and perspectives

We summarize recent developments in understanding the concept of generalized parton distributions (GPDs), its relation to nucleon structure, and its application to high-Q2 electroproduction processes. Following a brief review of QCD factorization and transverse nucleon structure, we discuss (a) new theoretical methods for the analysis of deeply-virtual Compton scattering (t-channel-based GPD parametrizations, dispersion relations); (b) the phenomenology of hard exclusive meson production (experimental tests of dominance of small-size configurations, model-independent comparative studies); (c) the role of GPDs in small-x physics and pp scattering (QCD dipole model, central exclusive diffraction). We emphasize the usefulness of the transverse spatial (or impact parameter) representation for both understanding the reaction mechanism in hard exclusive processes and visualizing the physical content of the GPDs.Comment: 10 pages, 6 figures. Proceedings of SPIN2008, University of Virginia, October 6-11, 200

The strong coupling constant at large distances

In this paper we discuss effective strong coupling constants. Those are well behaved in the low-Q^2 domain, contrarily to alpha_s from pQCD. We present an extraction of an effective strong coupling constant from Jefferson Lab polarized data at intermediate and low Q^2. We also show how these data, together with spin sum rules, allow us to obtain the effective coupling constant over the entire Q^2 range. We then discuss the relation between the experimentally extracted coupling constant and theoretical calculations at low Q^2. We conclude on the importance of such study for the application of the AdS/CFT correspondence to QCD.Comment: Proceedings for Spin2008 symposium. v2: added 2 referecences re. infrared fixed poin

Future Investigations of the Flavor Dependence of Sea Quark Helicities at STAR

The flavor dependence of polarized and unpolarized quark distributions in the nucleon can lead to insights into the formation of the sea. Drell-Yan measurements have pointed to flavor asymmetries in the unpolarized distributions. Collisions at sqrt{s}=500 GeV with polarized protons at RHIC will soon allow investigations of the flavor separated polarized quark distributions via W production to complement measurements from semi-inclusive DIS. We report on STAR's current plans, tracking upgrade, and expected sensitivities.Comment: 4 pages, to appear in the proceedings of the 18th International Spin Physics Symposium (Spin08), Charlottesville, Virginia, USA, October 6 - 11, 200

Parton Distributions in the Impact Parameter Space

Parton distributions in impact parameter space, which are obtained by Fourier transforming GPDs, exhibit a significant deviation from axial symmetry when the target and/or quark is transversely polarized. In combination with the final state interactions, this transverse deformation provides a natural mechanism for naive-T odd transverse single-spin asymmetries in semi-inclusive DIS. The deformation can also be related to the transverse force acting on the active quark in polarized DIS at higher twist.Comment: 9 pages, Proceedings Spin 200

Deep inelastic scattering from A=3 nuclei and the neutron structure function

We present a comprehensive analysis of deep inelastic scattering from He-3 and H-3, focusing in particular on the extraction of the free neutron structure function, F_2^n. Nuclear corrections are shown to cancel to within 1-2% for the isospin-weighted ratio of He-3 to H-3 structure functions, which leads to more than an order of magnitude improvement in the current uncertainty on the neutron to proton ratio F_2^n/F_2^p at large x. Theoretical uncertainties originating from the nuclear wave function, including possible non-nucleonic components, are evaluated. Measurement of the He-3 and H-3 structure functions will, in addition, determine the magnitude of the EMC effect in all A < 4 nuclei.Comment: 40 pages, 12 figures, to appear in Phys. Rev.

GPDs, their relationships with TMDs and related topics

Generalized Parton Distributions in the chiral odd sector are evaluated by examining their contribution to the quark proton helicity amplitudes, and by using Parity transformations to establish relations with the chiral even sector. The relations we find are valid in a spectator model where the recoiling system has total spin S=0,1. These relations allow us to fix the parameters for the chiral odd generalized parton distributions using results from a global analysis of unpolarized and longitudinally polarized experimental data in the kinematical region of intermediate Bjorken x and for Q2 in the multi-GeV region. Quantitative relations between chiral odd generalized parton distributions and transverse momentum dependent distributions are given, and their extension beyond spectator models is discussed. Contributions to the Generalized Transverse Momentum Distributions are obtained and considered in relation to observables. The related question about recoiling baryon polarizations is discussed