1,385 research outputs found
Phenomenological hadron form factors: shape and relativity
The use of relativistic quark models with simple parametric wave functions
for the understanding of the electromagnetic structure of nucleons together
with their electromagnetic transition to resonances is discussed. The
implications of relativity in the different ways it can be implemented in a
simple model are studied together with the role played by mixed symmetry
s-state and D-state deformations of the rest frame wave functions of the
nucleon and Delta resonance.Comment: To appear in the proceedings of "Shape of Hadrons" workshop, Athens,
Greece, 27-29 Apr 200
The status of the Excited Baryon Analysis Center
The Excited Baryon Analysis Center (EBAC), which is associated with the
Theory Group at Jefferson Laboratory, was initiated in 2006. Its main goal is
to extract and interpret properties of nucleon resonances (N*) from the world
data of meson production reactions induced by pions, photons and electrons. We
review the main accomplishments of the center since then and sketch its near
future perspectives.Comment: Invited plenary talk, to appear in the Proceedings of XIII
International Conference on Hadron Spectroscopy, November 29 - December 4,
2009, Florida State University. (v2, references added, fig6 slightly
modified
Coupled channel study of photoproduction
A coupled channel model with , and channels has been
used to analyze the recent data of . The non-resonant
interactions within the subspace are derived from effective
Lagrangians using a unitary transformation method. The direct photoproduction
reaction is obtained from a chiral constituent quark model with breaking. Missing baryon resonances issues are briefly discussed.Comment: Part of the proceedings of the International Workshop on the Physics
of Excited Baryons NSTAR05, 12-15 October 2005, Tallahassee, Florida, US
Spin mixing in colliding spinor condensates: formation of an effective barrier
The dynamics of F=1 spinor condensates initially prepared in a double-well
potential is studied in the mean field approach. It is shown that a small seed
of atoms on a system with initially well separated m=1 and m=-1
condensates has a dramatic effect on their mixing dynamics, acting as an
effective barrier for a remarkably long time. We show that this effect is due
to the spinor character of the system, and provides an observable example of
the interplay between the internal spin dynamics and the macroscopic evolution
of the magnetization in a spinor Bose-Einstein condensate.Comment: Accepted for publication at the Europhysics Letter
A model for the Delta(1600) resonance and gamma N -> Delta(1600) transition
A covariant spectator constituent quark model is applied to study the gamma N
-> Delta(1600) transition. Two processes are important in the transition: a
photon couples to the individual quarks of the Delta(1600) core (quark core),
and a photon couples to the intermediate pion-baryon states (pion cloud). While
the quark core contributions are estimated assuming Delta(1600) as the first
radial excitation of Delta(1232), the pion cloud contributions are estimated
based on an analogy with the gamma N -> Delta(1232) transition. To estimate the
pion cloud contributions in the gamma N -> Delta(1600) transition, we include
the relevant intermediate states, pi-N, pi-Delta, pi-N(1440) and
pi-Delta(1600). Dependence on the four-momentum transfer squared, Q2, is
predicted for the magnetic dipole transition form factor, GM*(Q2), as well as
the helicity amplitudes, A_1/2(Q2) and A_3/2(Q2). The results at Q2=0 are
compared with the existing data.Comment: To appear in Phys. Rev. D. Version with small modifications. 14
pages, 6 figures and 3 table
Search for missing baryon resonances via associated strangeness photoproduction
Differential cross-section and single polarization observables in the process
gamma p --> K^+ Lambda are investigated within a constituent quark model and a
dynamical coupled-channel formalism. The effects of two new nucleon resonances
and of the K*(892)- and K1(1270)-exchanges are briefly presented.Comment: Contributed paper to the IVth International Conference on Quarks and
Nuclear Physics, Madrid June 5-10, 200
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