89 research outputs found
Generalized parton distributions and the structure of the nucleon
Generalized parton distributions have been introduced in recent years as a
suitable theoretical tool to study the structure of the nucleon. Unifying the
concepts of parton distributions and hadronic form factors, they provide a
comprehensive framework for describing the quark and gluon structure of the
nucleon. In this review their formal properties and modeling are discussed,
summarizing the most recent developments in the phenomenological description of
these functions. The status of available data is also presented.Comment: 62 pages; 24 figures; version to appear in "La Rivista del Nuovo
Cimento
Electromagnetic Productions of KLambda and KSigma on the Nucleons
We briefly review the progress and problems in the electromagnetic production
of KLambda on the nucleon. The problem of the data discrepancy in this channel
as well as the corresponding physics consequence are highlighted. We also
discuss the effect of the new beam-recoil polarization data Cx and Cz on our
analysis. For this purpose we use the isobar model Kaon-Maid and a recent
multipoles model that can describe recent experimental data. We also present a
new multipoles model for the KSigma channels to complete our analysis.Comment: 8 pages, 6 figures, invited talk at 6th International Conference on
Perspectives in Hadronic Physics, Trieste, Italy, 12-16 May 200
Hard Break-Up of Two-Nucleons and QCD Dynamics of NN Interaction
We discus recent developments in theory of high energy two-body break-up of
few-nucleon systems. The characteristics of these reactions are such that the
hard two-body quasielastic subprocess can be clearly separated from the
accompanying soft subprocesses. We discuss in details the hard rescattering
model(HRM) in which hard photodisintegration develops in two stages. At first,
photon knocks-out an energetic quark which rescatters subsequently with a quark
of the other nucleon. The latter provides a mechanism of sharing the initial
high momentum of the photon between two outgoing nucleons. This final state
hard rescattering can be expressed through the hard NN scattering amplitude.
Within HRM we discuss hard break-up reactions involving D and 3He targets and
demonstrate how these reactions are sensitive to the dynamics of hard pn and pp
interaction. Another development of HRM is the prediction of new helicity
selection mechanism for hard two-body reactions, which was apparently confirmed
in the recent JLab experiment.Comment: Invited talk at 6th International Conference on Perspective in
Hadronic Physics, Trieste, Italy, 12-18 May 2008. Submitted to AIP Conf.Pro
Exploring the transverse spin structure of the nucleon
We discuss our present understanding of the transverse spin structure of the
nucleon and of related properties originating from parton transverse motion.
Starting from the transversity distribution and the ways to access it, we then
address the role played by spin and transverse momentum dependent (TMD)
distributions in azimuthal and transverse single spin asymmetries. The latest
extractions of the Sivers, Collins and transversity functions are also
presented.Comment: 8 pages, 6 ps figures, uses aipproc.cls. Invited talk at "6th
International Conference on Perspectives in Hadronic Physics (Hadron 08)",
Trieste, Italy, 12-18 May 2008. Submitted to AIP Conf.Pro
Electromagnetic Transition Form Factors of Nucleon Resonances
Recent measurements of nucleon resonance transition form factors with CLAS at
Jefferson Lab are discussed. The new data resolve a long-standing puzzle of the
nature of the Roper resonance, and confirm the assertion of the symmetric
constituent quark model of the Roper as the first radial excitation of the
nucleon. The data on production at high confirm the slow fall
off of the transition form factor with , and better
constrain the branching ratios and .
Also, new results on the transition amplitudes for the resonance
are presented showing a rapid change from helicity 3/2 dominance seen at the
real photon point to helicty 1/2 dominance at higher .Comment: 5 pages, 7 figure
Electromagnetic Form Factors of Hadrons in Quantum Field Theories
In this talk, recent results are presented of calculations of electromagnetic
form factors of hadrons in the framework of two quantum field theories (QFT),
(a) Dual-Large QCD (Dual-) for the pion, proton, and
, and (b) the Kroll-Lee-Zumino (KLZ) fully renormalizable Abelian
QFT for the pion form factor. Both theories provide a QFT platform to improve
on naive (tree-level) Vector Meson Dominance (VMD). Dual- provides
a tree-level improvement by incorporating an infinite number of zero-width
resonances, which can be subsequently shifted from the real axis to account for
the time-like behaviour of the form factors. The renormalizable KLZ model
provides a QFT improvement of VMD in the framework of perturbation theory. Due
to the relative mildness of the coupling, and the size of loop
suppression factors, the perturbative expansion is well defined in spite of
this being a strong coupling theory. Both approaches lead to considerable
improvements of VMD predictions for electromagnetic form factors, in excellent
agreement with data.Comment: Invited talk at the Sixth International Conference on Perspectives in
Hadronic Physics, ICTP, Trieste, Italy, May 200
Short-range nucleon correlations and neutrino emission by neutron stars
We argue that significant probability of protons with momenta above their
Fermi surface leads for proton concentrations p/n > 1/8 to the enhancement of
termally excited direct and modified URCA processes within a cold neutron star,
and to a nonzero probability of direct URCA processes for small proton
concentrations (p/n < 1/8). We evaluate high momentum tails of neutron, proton
and electrons distributions within a neutron star. We expect also significantly
faster neutrino cooling of hyperon stars.Comment: 7 pages, updated version to be published in Proceedings of Sixth
International Conference on Perspectives in Hadronic Physics, Trieste, May
200
Studies of Parton Propagation and Hadron Formation in the Space-Time Domain
Over the past decade, new data from HERMES, Jefferson Lab, Fermilab, and RHIC
that connect to parton propagation and hadron formation have become available.
Semi-inclusive DIS on nuclei, the Drell-Yan reaction, and heavy-ion collisions
all bring different kinds of information on parton propagation within a medium,
while the most direct information on hadron formation comes from the DIS data.
Over the next decade one can hope to begin to understand these data within a
unified picture. We briefly survey the most relevant data and the common
elements of the physics picture, then highlight the new Jefferson Lab data, and
close with a prospective for the future.Comment: Invited talk delivered at the Sixth International Conference on
Perspectives in Hadronic Physics, ICTP, Trieste, Italy, 12-16 May 2008. 8
pages, 5 figure
Relativistic Quark-Model Results for Baryon Ground and Resonant States
Latest results from a study of baryon ground and resonant states within
relativistic constituent quark models are reported. After recalling some
typical spectral properties, the description of ground states, especially with
regard to the nucleon and hyperon electromagnetic structures, is addressed. In
the following, recent covariant predictions for pion, eta, and kaon partial
decay widths of light and strange baryon resonances below 2 GeV are summarized.
These results exhibit a characteristic pattern that is distinct from
nonrelativistic or relativized decay studies performed so far. Together with a
detailed analysis of the spin, flavor, and spatial structures of the wave
functions, it supports a new and extended classification scheme of baryon
ground and resonant states into SU(3) flavor multiplets
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