39,216 research outputs found
Higher and missing resonances in omega photoproduction
We study the role of the nucleon resonances () in
photoproduction by using the quark model resonance parameters predicted by
Capstick and Roberts. The employed and
amplitudes include the configuration mixing effects due to the residual
quark-quark interactions. The contributions from the nucleon resonances are
found to be important in the differential cross sections at large scattering
angles and various spin observables. In particular, the parity asymmetry and
beam-target double asymmetry at forward scattering angles are suggested for a
crucial test of our predictions. The dominant contributions are found to be
from , a missing resonance, and which is
identified as the of the Particle Data Group.Comment: 8 pages, LaTeX with ws-p8-50x6-00.cls, 4 figures (5 eps files), Talk
presented at the NSTAR2001 Workshop on the Physics of Excited Nucleons,
Mainz, Germany, Mar. 7-10, 200
Electromagnetic production of vector mesons at low energies
We have investigated exclusive photoproduction of light vector mesons
(, and ) on the nucleon at low energies. In order to
explore the questions concerning the so-called missing nucleon resonances, we
first establish the predictions from a model based on the Pomeron and meson
exchange mechanisms. We have also explored the contributions due to the
mechanisms involving - and -channel intermediate nucleon state. Some
discrepancies found at the energies near threshold and large scattering angles
suggest a possibility of using this reaction to identify the nucleon
resonances.Comment: 9 pages, LaTeX with sprocl.sty, 5 figures (11 eps files), Talk
presented at the NSTAR2000 Workshop, The Physics of Excited Nucleons,
Jefferson Lab., Newport News, Feb. 16-19, 200
Charmonium-Nucleon Dissociation Cross Sections in the Quark Model
Charmonium dissociation cross sections due to flavor-exchange
charmonium-baryon scattering are computed in the constituent quark model. We
present results for inelastic and scattering amplitudes
and cross sections into 46 final channels, including final states composed of
various combinations of , , , and . These results
are relevant to experimental searches for the deconfined phase of quark matter,
and may be useful in identifying the contribution of initial
production to the open-charm final states observed at RHIC through the
characteristic flavor ratios of certain channels. These results are also of
interest to possible charmonium-nucleon bound states.Comment: 10 pages, 5 eps figures, revte
On the sign of the pi-rho-omega coupling constant
It is shown that the relative sign between the and
coupling constants can be determined most sensitively from production
processes in collisions. Recent data on these reactions clearly favor the
sign of the coupling constant which is opposite to that
inferred from studies of the photoproduction reaction in combination with the
vector meson dominance assumption and used by many authors. Implication of this
finding in the description of other reactions is discussed.Comment: 6 pages, 4 figures, REVTeX, to be published in Phys. Lett.
Higher Derivative CP(N) Model and Quantization of the Induced Chern-Simons Term
We consider higher derivative CP(N) model in 2+1 dimensions with the
Wess-Zumino-Witten term and the topological current density squared term. We
quantize the theory by using the auxiliary gauge field formulation in the path
integral method and prove that the extended model remains renormalizable in the
large N limit. We find that the Maxwell-Chern-Simons theory is dynamically
induced in the large N effective action at a nontrivial UV fixed point. The
quantization of the Chern-Simons term is also discussed.Comment: 8 pages, no figure, a minor change in abstract, added Comments on the
quantization of the Chern-Simons term whose coefficient is also corrected,
and some references are added. Some typos are corrected. Added a new
paragraph checking the equivalence between (3) and (5), and a related
referenc
Charmonium-hadron interactions from QCD
The heavy quark system is an excellent probe to learn about the QCD dynamics
at finite density. First, we discuss the properties of the and
meson at finite nucleon density. We discuss why their properties should change
at finite density and then introduce an exact QCD relation among these hadron
properties and the energy momentum tensor of the medium. Second, we discuss
attempts to calculate charmonium-hadron total cross section using effective
hadronic models and perturbative QCD. We emphasize a recent calculation, where
the cross section is derived using QCD factorization theorem. We conclude by
discussing some challenges for SIS 200.Comment: 8 pages, Presented at 6th International Conference on Strange Quarks
in Matter: 2001: A Flavorspace Odyssey (SQM2001), Frankfurt, Germany, 25-29
Sep 2001, submitted to J. Phys.
Isospin particle on with arbitrary number of supersymmetries
We study the supersymmetric quantum mechanics of an isospin particle in the
background of spherically symmetric Yang-Mills gauge field. We show that on
the number of supersymmetries can be made arbitrarily large for a
specific choice of the spherically symmetric SU(2) gauge field. However, the
symmetry algebra containing the supercharges becomes nonlinear if the number of
fermions is greater than two. We present the exact energy spectra and
eigenfunctions, which can be written as the product of monopole harmonics and a
certain isospin state. We also find that the supersymmetry is spontaneously
broken if the number of supersymmetries is even.Comment: 6 page
Epitaxial aluminium-nitride tunnel barriers grown by nitridation with a plasma source
High critical current-density (10 to 420 kA/cm^2)
superconductor-insulator-superconductor tunnel junctions with aluminium nitride
barriers have been realized using a remote nitrogen plasma from an inductively
coupled plasma source operated in a pressure range of 10^{-3} to 10^{-1} mbar.
We find a much better reproducibility and control compared to previous work.
From the current-voltage characteristics and cross-sectional TEM images it is
inferred that, compared to the commonly used AlO_x barriers, the
poly-crystalline AlN barriers are much more uniform in transmissivity, leading
to a better quality at high critical current-densities.Comment: 3 pages, 3 figures, accepted for publication in AP
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