Flavor Asymmetries in the Proton and Semi-Inclusive Processes

Semi-inclusive electron scattering provides a powerful tool with which to study the spin and flavor distributions in the proton. Greater kinematic coverage at the proposed Electron-Polarized Ion Collider facility will enable the valence d/u ratio to be determined at large x through pion production. At small x, pion production can be used to extract the d-bar/u-bar ratio, complementing existing semi-inclusive measurements by HERMES, and Drell-Yan data from Fermilab. Asymmetries in heavier quark flavors can also be probed by tagging strange and charm hadrons in the final state.Comment: 15 pages, 6 figures, presented at the Electron-Polarized Ion Collider Workshop, IUCF, April 199

Quark-Hadron Duality in Electron Scattering

Quark-hadron duality addresses some of the most fundamental issues in strong interaction physics, in particular the nature of the transition from the perturbative to non-perturbative regions of QCD. I summarize recent developments in quark-hadron duality in lepton-hadron scattering, and outline how duality can be studied at future high-luminosity facilities such as Jefferson Lab at 12 GeV, or an electron-hadron collider such as EPIC.Comment: 5 pages, 2 figures, talk presented at the Second Workshop on Physics with an Electron Polarized Light-Ion Collider (EPIC), MIT, Sep.14-16, 200

Quark-hadron duality in electron-pion scattering

We explore the relationship between exclusive and inclusive electromagnetic scattering from the pion, focusing on the transition region at intermediate Q^2. Combining Drell-Yan data on the leading twist quark distribution in the pion with a model for the resonance region at large x, we calculate QCD moments of the pion structure function over a range of Q^2, and quantify the role of higher twist corrections. Using a parameterization of the pion elastic form factor and phenomenological models for the pi -> rho transition form factor, we further test the extent to which local duality may be valid for the pion.Comment: 23 pages, 7 figures, to appear in Eur. J. Phys.

Nucleon structure at large x: nuclear effects in deuterium

I review quark momentum distributions in the nucleon at large momentum fractions x. Particular attention is paid to the impact of nuclear effects in deuterium on the d/u quark distribution ratio as x -> 1. A new global study of parton distributions, using less restrictive kinematic cuts in Q^2 and W^2, finds strong suppression of the d quark distribution once nuclear corrections are accounted for.Comment: to appear in Achievements and New Directions in Subatomic Physics: Festschrift in Honour of Tony Thomas' 60th Birthday, Adelaide, Australia, 15-19 Feb. 2010, ed. W. Melnitchou

QCD and the Structure of the Nucleon in Electron Scattering

The internal structure of the nucleon is discussed within the context of QCD. Recent progress in understanding the distribution of flavor and spin in the nucleon is reviewed, and prospects for extending our knowledge of nucleon structure in electron scattering experiments at modern facilities such as Jefferson Lab are outlined.Comment: 52 pages, 11 figures, lectures presented at the 1999 Hampton University Graduate Studies (HUGS) summer school, Jefferson La

Flavor Decomposition of the Nucleon

I review some recent developments in the study of quark flavor distributions in the nucleon, including (i) valence quark distributions and the quark-hadron duality prediction for the x -> 1 d/u ratio (ii) sea quark asymmetries and electromagnetic form factors (iii) strange quarks in the nucleon.Comment: 12 pages, 6 figures, extended version of talk presented at the Workshop on Exclusive & Semi-Exclusive Processes at High Momentum Transfer, Jefferson Lab, June 1999; minor typos correcte

Asymmetric Quarks in the Proton

Asymmetries in the quark momentum distributions in the proton reveal fundamental aspects of strong interaction physics. Differences between u-bar and d-bar quarks in the proton sea provide insight into the dynamics of the pion cloud around the nucleon and the nature of chiral symmetry breaking. Polarized flavor asymmetries allow the effects of pion clouds to be disentangled from those of antisymmetrization. Asymmetries between s and s-bar quark distributions in the nucleon are also predicted from the chiral properties of QCD.Comment: 7 pages, 2 figures, talk presented at the 3rd International Symposium on Symmetries in Subatomic Physics, Adelaide, Australia, March 200

Neutron Structure Functions From Nuclear Data

The spin-averaged structure function of the neutron, F_2^n, is extracted from recent deuteron data, taking into account the small but significant corrections due to nuclear effects in the deuteron. At small x, the F_2D/F_2p ratio measured by the New Muon and Fermilab E665 Collaborations is interpreted to suggest a small amount of shadowing in deuterium, which acts to enhance F_2^n for x < 0.1. A careful treatment of Fermi motion, binding and nucleon off-shell effects in the deuteron also indicates that the neutron/proton structure function ratio as x -> 1 is consistent with the perturbative QCD expectation of 3/7, but larger than the traditional value of 1/4.Comment: 16 pages RevTeX, 5 postscript figures, presented at 2nd. Cracow Epiphany Conference on Proton Structure, Jan. 199