3,675 research outputs found
Photon-meson transition form factors of light pseudoscalar mesons
The photon-meson transition form factors of light pseudoscalar mesons , , and are systematically calculated in a
light-cone framework, which is applicable as a light-cone quark model at low
and is also physically in accordance with the light-cone pQCD approach
at large . The calculated results agree with the available experimental
data at high energy scale. We also predict the low behaviors of the
photon-meson transition form factors of , and , which are measurable in process via Primakoff
effect at JLab and DESY.Comment: 22 Latex pages, 7 figures, Version to appear in PR
High-Energy QCD Asymptotics of Photon-Photon Collisions
The high-energy behaviour of the total cross section for highly virtual
photons, as predicted by the BFKL equation at next-to-leading order (NLO) in
QCD, is discussed. The NLO BFKL predictions, improved by the BLM optimal scale
setting, are in good agreement with recent OPAL and L3 data at CERN LEP2. NLO
BFKL predictions for future linear colliders are presented.Comment: Latex, 7 pages, 4 figure
Sum rules for light-by-light scattering
We derive a set of sum rules for the light-by-light scattering and fusion:
, and verify them in lowest order QED calculations. A
prominent implication of these sum rules is the superconvergence of the
helicity-difference total cross-section for photon fusion, which in the hadron
sector reveals an intricate cancellation between the pseudoscalar and tensor
mesons. An experimental verification of superconvergence of the polarized
photon fusion into hadrons is called for, but will only be possible at and colliders with both beams polarized. We also show how
the sum rules can be used to measure various contributions to the low-energy
light-by-light scattering.Comment: 4 pages, 3 figures; minor corrections, published versio
Gluon Virtuality and Heavy Sea Quark Contributions to the Spin-Dependent g_1 Structure Function
We analyze the quark mass dependence of photon gluon fusion in polarized deep
inelastic scattering for both the intrinsic and extrinsic gluon distributions
of the nucleon. We calculate the effective number of flavors for each of the
heavy and light quark photon gluon fusion contributions to the first moment of
the spin-dependent structure function .Comment: LaTex, 19 page
Light-Cone Quantization and Hadron Structure
In this talk, I review the use of the light-cone Fock expansion as a
tractable and consistent description of relativistic many-body systems and
bound states in quantum field theory and as a frame-independent representation
of the physics of the QCD parton model. Nonperturbative methods for computing
the spectrum and LC wavefunctions are briefly discussed. The light-cone Fock
state representation of hadrons also describes quantum fluctuations containing
intrinsic gluons, strangeness, and charm, and, in the case of nuclei, "hidden
color". Fock state components of hadrons with small transverse size, such as
those which dominate hard exclusive reactions, have small color dipole moments
and thus diminished hadronic interactions; i.e., "color transparency". The use
of light-cone Fock methods to compute loop amplitudes is illustrated by the
example of the electron anomalous moment in QED. In other applications, such as
the computation of the axial, magnetic, and quadrupole moments of light nuclei,
the QCD relativistic Fock state description provides new insights which go well
beyond the usual assumptions of traditional hadronic and nuclear physics.Comment: LaTex 36 pages, 3 figures. To obtain a copy, send e-mail to
[email protected]
Intrinsic Charm of Vector Mesons: A Possible Solution of the "rho pi" Puzzle
An outstanding mystery of charmonium physics is why the J/\psi decays
prominently to pseudoscalar plus vector meson channels, such as J/\psi -> \rho
\pi and J/\psi -> K^*K, whereas the \psi'(2S) does not. We show that such
decays of J/\psi and their suppression for \psi'(2S) follow naturally from the
existence of intrinsic charm |qbar q cbar c> Fock components of the light
vector mesons.Comment: Latex, 11 page
Azimuthal Dependence of the Heavy Quark Initiated Contributions to DIS
We analyze the azimuthal dependence of the heavy-quark-initiated
contributions to the lepton-nucleon deep inelastic scattering (DIS). First we
derive the relations between the parton level semi-inclusive structure
functions and the helicity cross sections in the case of
arbitrary values of the heavy quark mass. Then the azimuth-dependent lepton-quark DIS is calculated in the helicity basis. Finally,
we investigate numerically the properties of the and
distributions caused by the photon-quark scattering (QS) contribution. It turns
out that, contrary to the basic photon-gluon fusion (GF) component, the QS
mechanism is practically -independent. This fact implies that
measurements of the azimuthal distributions in charm leptoproduction could
directly probe the charm density in the proton.Comment: 11 pages, 4 figures, revtex4, published versio
Nucleon-Quarkonium Elastic Scattering and the Gluon Contribution to Nucleon Spin
It is shown that the amplitude for the scattering of a heavy quarkonium
system from a nucleon near threshold is completely determined by the fraction
of angular momentum, as well as linear momentum, carried by gluons in the
nucleon. A form for the quarkonium-nucleon non-relativistic potential is
derived.Comment: 4 pages, no figures. Author's e-mail: [email protected]
Systematics of Heavy Quark Production at HERA
We discuss heavy quark and quarkonium production in various kinematic regions
at the HERA ep collider. In contrast to fixed target experiments, collider
kinematics allows the possibility of detailed measurements of particle
production in the proton fragmentation region. One thus can study parton
correlations in the proton Fock states materialized by the virtual photon
probe. We discuss various configurations of inelastic electron-proton
scattering, including peripheral, diffractive, and deep inelastic processes. In
particular, we show that intrinsic heavy quark Fock states can be identified by
the observation of quarkonium production at large and a low mean
transverse momentum which is insensitive to the virtuality of the photon.Comment: 17 pages, postscript. To obtain a copy of this paper send e-mail to
[email protected]
The Spin and Flavor Content of Intrinsic Sea Quarks
The intrinsic quark-antiquark pairs generated by the minimal energy nonperturbative meson-baryon fluctuations in the nucleon sea provide a consistent framework for understanding a number of empirical anomalies observed in the deep inelastic quark-parton structure of nucleons: the flavor asymmetry of the nucleon sea implied by the violation of Gottfried sum rule, the proton spin problem implied by the violation of the Ellis-Jaffe sum rule, and the outstanding conflict between two different determinations of the strange quark sea in the nucleon
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