1,464 research outputs found
Sensitivity of tensor analyzing power in the process to the longitudinal isoscalar form factor of the Roper resonance electroexcitation
The tensor analyzing power of the process , for forward
deuteron scattering in the momentum interval 3.7 to 9 GeV/c, is studied in the
framework of exchange in an algebraic collective model for the
electroexcitation of nucleon resonances. We point out a special sensitivity of
the tensor analyzing power to the isoscalar longitudinal form factor of the
Roper resonance excitation. The main argument is that the ,
and resonances have only isovector longitudinal
form factors. It is the longitudinal form factor of the Roper excitation, which
plays an important role in the dependence of the tensor analyzing power. We
discuss possible evidence of swelling of hadrons with increasing excitation
energy.Comment: 12 pages, 10 figure
Masses and magnetic moments of pentaquarks
We discuss the spectroscopy of pentaquarks. The quantum numbers of the ground
state depend on the interplay between spin-flavor and orbital contributions to
the energy. The magnetic moments of the lowest pentaquark state with negative
and positive parity are found to be 0.382 \mu_N and 0.089 \mu_n, respectively.Comment: 15 pages, 4 figures, 3 tables (text rewritten, extra figure added,
essential results unchanged
Mass spectrum of pentaquarks
We discuss the properties of the pentaquark in a collective stringlike model
with a nonplanar configuration of the four quarks and the antiquark. In an
application to the mass spectrum of exotic Theta baryons, we find that the
ground state pentaquark has angular momentum and parity J(p)=1/2(-) and a small
magnetic moment of 0.382 nuclear magnetons. The decay width is suppressed by
the spatial overlap with the decay products.Comment: 8 pages, 3 figures, 1 table, invited talk at 23rd International
Workshop on Nuclear Theory, June 14-19, 2004, Rila, Bulgari
Re-analysis of the nucleon space- and time-like electromagnetic form factors in a two-component model
Recent experimental data on space-like and time-like form factors of the
nucleon are analyzed in terms of a two-component model with a quark-like
intrinsic three-quark structure and quark-antiquark pairs.Comment: 9 pages, 5 figures, accepted for publication as a Brief Report in
Physical Review
Angular momentum I ground state probabilities of boson systems interacting by random interactions
In this paper we report our systematic calculations of angular momentum
ground state probabilities () of boson systems with spin in the
presence of random two-body interactions. It is found that the P(0) dominance
is usually not true for a system with an odd number of bosons, while it is
valid for an even number of bosons, which indicates that the P(0) dominance is
partly connected to the even number of identical particles. It is also noticed
that the 's of bosons with spin do not follow the 1/N (,
referring to the number of independent two-body matrix elements) relation. The
properties of the 's obtained in boson systems with spin are
discussed.Comment: 8 pages and 3 figure
Many-body Systems Interacting via a Two-body Random Ensemble (I): Angular Momentum distribution in the ground states
In this paper, we discuss the angular momentum distribution in the ground
states of many-body systems interacting via a two-body random ensemble.
Beginning with a few simple examples, a simple approach to predict P(I)'s,
angular momenta I ground state (g.s.) probabilities, of a few solvable cases,
such as fermions in a small single-j shell and d boson systems, is given. This
method is generalized to predict P(I)'s of more complicated cases, such as even
or odd number of fermions in a large single-j shell or a many-j shell, d-boson,
sd-boson or sdg-boson systems, etc. By this method we are able to tell which
interactions are essential to produce a sizable P(I) in a many-body system. The
g.s. probability of maximum angular momentum is discussed. An
argument on the microscopic foundation of our approach, and certain matrix
elements which are useful to understand the observed regularities, are also
given or addressed in detail. The low seniority chain of 0 g.s. by using the
same set of two-body interactions is confirmed but it is noted that
contribution to the total 0 g.s. probability beyond this chain may be more
important for even fermions in a single-j shell. Preliminary results by taking
a displaced two-body random ensemble are presented for the I g.s.
probabilities.Comment: 39 pages and 8 figure
Spectroscopy of pentaquark states
We construct a complete classification of pentaquark states in terms of the
spin-flavour SU(6) representations. We find that only some definite SU(3)
representations are allowed, singlets, octets, decuplets, anti-decuplets,
27-plets and 35-plets. The latter three contain exotic states, which cannot be
constructed from three quarks only. This complete classification scheme is
general and model independent and is useful both for model builders and
experimentalists. The mass spectrum is obtained from a Gursey-Radicati type
mass formula, whose coefficients have been determined previously by a study of
qqq baryons. The ground state pentaquark which is identified with the recently
observed Theta(1540) state, is predicted to be an isosinglet anti-decuplet
state. Its parity depends on the interplay between the spin-flavour and orbital
contributions to the mass operator.Comment: 26 pages, 4 figures, 11 tables, revised version with 2 extra tables,
an updated list of references and expanded discussion of the results.
Accepted for publication in Eur. Phys. J.
Generic Rotation in a Collective SD Nucleon-Pair Subspace
Low-lying collective states involving many nucleons interacting by a random
ensemble of two-body interactions (TBRE) are investigated in a collective
SD-pair subspace, with the collective pairs defined dynamically from the
two-nucleon system. It is found that in this truncated pair subspace collective
vibrations arise naturally for a general TBRE hamiltonian whereas collective
rotations do not. A hamiltonian restricted to include only a few randomly
generated separable terms is able to produce collective rotational behavior, as
long as it includes a reasonably strong quadrupole-quadrupole component.
Similar results arise in the full shell model space. These results suggest that
the structure of the hamiltonian is key to producing generic collective
rotation.Comment: 11 pages, 5 figure
Spectroscopy with random and displaced random ensembles
Due to the time reversal invariance of the angular momentum operator J^2, the
average energies and variances at fixed J for random two-body Hamiltonians
exhibit odd-even-J staggering, that may be especially strong for J=0. It is
shown that upon ensemble averaging over random runs, this behaviour is
reflected in the yrast states. Displaced (attractive) random ensembles lead to
rotational spectra with strongly enhanced BE2 transitions for a certain class
of model spaces. It is explained how to generalize these results to other forms
of collectivity.Comment: 4 pages, 4 figure
A general algebraic model for molecular vibrational spectroscopy
We introduce the Anharmonic Oscillator Symmetry Model to describe vibrational
excitations in molecular systems exhibiting high degree of symmetry. A
systematic procedure is proposed to establish the relation between the
algebraic and configuration space formulations, leading to new interactions in
the algebraic model. This approach incorporates the full power of group
theoretical techniques and provides reliable spectroscopic predictions. We
illustrate the method for the case of -triatomic molecules.Comment: 35 pages TEX, submitted to Annals of Physics (N.Y.
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