18 research outputs found
A Naturally Narrow Positive Parity Theta^+
We present a consistent color-flavor-spin-orbital wave function for a
positive parity Theta^+ that naturally explains the observed narrowness of the
state. The wave function is totally symmetric in its flavor-spin part and
totally antisymmetric in its color-orbital part. If flavor-spin interactions
dominate, this wave function renders the positive parity Theta^+ lighter than
its negative parity counterpart. We consider decays of the Theta^+ and compute
the overlap of this state with the kinematically allowed final states. Our
results are numerically small. We note that dynamical correlations between
quarks are not necessary to obtain narrow pentaquark widths.Comment: 10 pages, 1 figure, Revtex4, two-column format, version to be
published in Phys. Rev. D, includes numerical estimates of decay width
Magnetic Moment of The Pentaquark State
We have calculated the magnetic moment of the recently observed
pentaquark in the framework of the light cone QCD sum rules using the photon
distribution amplitudes. We find that ,
which is quite small. We also compare our result with predictions of other
groups.Comment: 1 eps figure, 13 page
Z^* Resonances: Phenomenology and Models
We explore the phenomenology of, and models for, the Z^* resonances, the
lowest of which is now well established, and called the Theta. We provide an
overview of three models which have been proposed to explain its existence
and/or its small width, and point out other relevant predictions, and potential
problems, for each. The relation to what is known about KN scattering,
including possible resonance signals in other channels, is also discussed.Comment: 29 pages, uses RevTeX4; expanded version (published form
A characterization of ecosystem services, drivers and values of two watersheds in São Paulo State, Brazil
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
The theta^+ baryon in soliton models: large Nc QCD and the validity of rigid-rotor quantization
A light collective theta+ baryon state (with strangeness +1) was predicted
via rigid-rotor collective quantization of SU(3) chiral soliton models. This
paper explores the validity of this treatment. A number of rather general
analyses suggest that predictions of exotic baryon properties based on this
approximation do not follow from large Nc QCD. These include an analysis of the
baryon's width, a comparison of the predictions with general large Nc
consistency conditions of the Gervais-Sakita-Dashen-Manohar type; an
application of the technique to QCD in the limit where the quarks are heavy; a
comparison of this method with the vibration approach of Callan and Klebanov;
and the 1/Nc scaling of the excitation energy. It is suggested that the origin
of the problem lies in an implicit assumption in the that the collective motion
is orthogonal to vibrational motion. While true for non-exotic motion, the
Wess-Zumino term induces mixing at leading order between collective and
vibrational motion with exotic quantum numbers. This suggests that successful
phenomenological predictions of theta+ properties based on rigid-rotor
quantization were accidental.Comment: 19 pages; A shorter more readable versio