1,367 research outputs found
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
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