64 research outputs found
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
Coupled-channel study of gamma p --> K+ Lambda
A coupled-channel (CC) approach has been developed to investigate kaon
photoproduction on the nucleon. In addition to direct K+ Lambda production, our
CC approach accounts for strangeness production including K+ Lambda final state
interactions with both pi0 p and pi+ n intermediate states. Calculations for
the gamma p --> K+ Lambda reaction have been performed, and compared with the
recent data from SAPHIR, with emphasis on the CC effects. We show that the CC
effects are significant at the level of inducing 20% changes on total cross
sections; thereby, demonstrating the need to include pi N channels to correctly
describe the gamma p --> K+ Lambda reaction.Comment: 12 pages, 6 eps figures, uses elsart.cls, submitted to Phys.Lett.B;
v2: added paragraph in section
Analytic calculation of energies and wave functions of the quartic and pure quartic oscillators
Ground state energies and wave functions of quartic and pure quartic
oscillators are calculated by first casting the Schr\"{o}dinger equation into a
nonlinear Riccati form and then solving that nonlinear equation analytically in
the first iteration of the quasilinearization method (QLM). In the QLM the
nonlinear differential equation is solved by approximating the nonlinear terms
by a sequence of linear expressions. The QLM is iterative but not perturbative
and gives stable solutions to nonlinear problems without depending on the
existence of a smallness parameter. Our explicit analytic results are then
compared with exact numerical and also with WKB solutions and it is found that
our ground state wave functions, using a range of small to large coupling
constants, yield a precision of between 0.1 and 1 percent and are more accurate
than WKB solutions by two to three orders of magnitude. In addition, our QLM
wave functions are devoid of unphysical turning point singularities and thus
allow one to make analytical estimates of how variation of the oscillator
parameters affects physical systems that can be described by the quartic and
pure quartic oscillators.Comment: 8 pages, 12 figures, 1 tabl
Dynamical coupled-channel model of kaon-hyperon interactions
The pi N --> KY and KY --> KY reactions are studied using a dynamical
coupled-channel model of meson-baryon interactions at energies where the baryon
resonances are strongly excited. The channels included are: pi N, K \Lambda,
and K\Sigma. The resonances considered are: N^* [S_{11}(1650), P_{11}(1710),
P_{13}(1720),D_{13}(1700)]; \Delta^* [S_{31}(1900), P_{31}(1910),
P_{33}(1920)]; \Lambda ^* [S_{01}(1670), P_{01}(1810)] \Sigma^* [P_{11}(1660),
D_{13}(1670)]; and K^*(892). The basic non-resonant \pi N --> KY and KY --> KY
transition potentials are derived from effective Lagrangians using a unitary
transformation method. The dynamical coupled-channel equations are simplified
by parametrizing the pi N -->pi N amplitudes in terms of empirical pi N
partial-wave amplitudes and a phenomenological off-shell function. Two models
have been constructed. Model A is built by fixing all coupling constants and
resonance parameters using SU(3) symmetry, the Particle Data Group values, and
results from a constituent quark model. Model B is obtained by allowing most of
the parameters to vary around the values of model A in fitting the data. Good
fits to the available data for pi^- p to K^0 \Lambda, K^0 \Sigma^0 have been
achieved. The investigated kinematics region in the center-of-mass frame goes
from threshold to 2.5 GeV. The constructed models can be imbedded into
associated dynamical coupled-channel studies of kaon photo- and
electro-production reactions.Comment: 35 pages, 11 Figure
Dynamical coupled-channel approach to hadronic and electromagnetic production of kaon-hyperon on the proton
A dynamical coupled-channel formalism for processes and
is presented which provides a comprehensive investigation of
recent data on the reaction. The non-resonant
interactions within the subspace are derived from effective
Lagrangians, using a unitary transformation method. The calculations of
photoproduction amplitudes are simplified by casting the coupled-channel
equations into a form such that the empirical amplitudes
are input and only the parameters associated with the channel are
determined by performing -fits to all of the available data for and . Good
agreement between our models and those data are obtained. In the fits to channels, most of the parameters are constrained within of
the values given by the Particle Data Group and/or quark model predictions,
while for parameters, ranges compatible with broken
symmetry are imposed. The main reaction mechanisms in photoproduction are singled out and issues related to newly suggested
resonances , , and are studied. Results illustrating
the importance of using a coupled-channel treatment are reported. Meson cloud
effects on the transitions are also discussed.Comment: Accepted Physical Review
Pseudoscalar meson photoproduction: from known to undiscovered resonances
The role of dynamics in spin observables for pseudoscalar meson
photoproduction is investigated using a density matrix approach in a multipole
truncated framework. Extraction of novel rules for and reactions based on resonance dominance, and on
other broad and reasonable dynamical assumptions, are discussed. Observables
that are particularly sensitive to missing nucleonic resonances predicted by
quark-based approaches, are singled out.Comment: 22 pages, latex, 3 figure
Relativistic Effect on Low-Energy Nucleon-Deuteron Scattering
The relativistic effect on differential cross sections, nucleon-to-nucleon
and nucleon-to-deuteron polarization transfer coefficients, and the spin
correlation function, of nucleon-deuteron elastic scattering is investigated
employing several three-dimensional relativistic three-body equations and
several nucleon-nucleon potentials. The polarization transfer coefficients are
found to be sensitive to the details of the nucleon-nucleon potentials and the
relativistic dynamics employed, and prefer trinucleon models with the correct
triton binding energy. (To appear in Phys. Rev. C)Comment: pages: 21, LaTex text + 7 ps-figures at the en
Pion interaction with the trinucleon up to the eta production threshold
Pion elastic, charge exchange scattering and induced eta production on the
trinucleon systems are investigated in a coupled-channels approach in momentum
space with Fadeev wave functions. The channel is
included using an isobar model with S-, P-, and D-wave resonances. While the
coherent reactions like He(He can be reasonably well reproduced
up to =500 MeV, large discrepancies appear for the incoherent
processes, He(H and He(H at backward
angles and energies above -resonance. In the forward direction the
calculations underestimate the experimental measurements very
close to threshold but agreement with the data improves with increasing pion
energy. Predictions are made for the asymmetries of the various reactions on
polarized He.Comment: 40 pages, 12 figures (available from the authors), Mainz preprint
MKPH-T-92-1
Exclusive Photoproduction of Large Momentum-Transfer K and K* Mesons
The reactions gamma p -> K+ Lambda and gamma p -> K* Lambda are analyzed
within perturbative QCD, allowing for diquarks as quasi-elementary constituents
of baryons. The diquark-model parameters and the quark-diquark distribution
amplitudes of proton and Lambda are taken from previous investigations of
electromagnetic baryon form factors and Compton-scattering off protons.
Unpolarized differential cross sections and polarization observables are
computed for different choices of the K and K* distribution amplitudes. The
asymptotic form of the K distribution amplitude (proportional to x1 x2) is
found to provide a satisfactory description of the K photoproduction data.Comment: 32 pages, 7 figures available as tared, compressed and uuencoded
PS-file
Moscow-type NN-potentials and three-nucleon bound states
A detailed description of Moscow-type (M-type) potential models for the NN
interaction is given. The microscopic foundation of these models, which appear
as a consequence of the composite quark structure of nucleons, is discussed.
M-type models are shown to arise naturally in a coupled channel approach when
compound or bag-like six-quark states, strongly coupled to the NN channel, are
eliminated from the complete multiquark wave function. The role of the
deep-lying bound states that appear in these models is elucidated. By
introducing additional conditions of orthogonality to these compound six-quark
states, a continuous series of almost on-shell equivalent nonlocal interaction
models, characterized by a strong reduction or full absence of a local
repulsive core (M-type models), is generated. The predictions of these
interaction models for 3N systems are analyzed in detail. It is shown that
M-type models give, under certain conditions, a stronger binding of the 3N
system than the original phase-equivalent model with nodeless wave functions.
An analysis of the 3N system with the new versions of the Moscow NN potential
describing also the higher even partial waves is presented. Large deviations
from conventional NN force models are found for the momentum distribution in
the high momentum region. In particular, the Coulomb displacement energy for
nuclei ^3He - ^3H displays a promising agreement with experiment when the ^3H
binding energy is extrapolated to the experimental value.Comment: 23 pages Latex, 9 figures, to appear in Phys.Rev.
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