58 research outputs found
Photoproduction of Theta baryon from the neutron
We study photoproduction reactions for Theta^+, which was recently observed
as a candidate of an exotic five quark state uudd(bar s). We employ effective
lagrangian interactions in the linear and non-linear formalism of chiral
symmetry and investigate two cases of spin and parity of Theta^+, J^P = 1/2^+
and 1/2^-. We calculate cross sections and discuss possibilities to
discriminate one from the other.Comment: 14 pages, 19 figure
Phenomenology of the Pentaquark Antidecuplet
We consider the mass splittings and strong decays of members of the
lowest-lying pentaquark multiplet, which we take to be a parity-odd
antidecuplet. We derive useful decompositions of the quark model wave functions
that allow for easy computation of color-flavor-spin matrix elements. We
compute mass splittings within the antidecuplet including spin-color and
spin-isospin interactions between constituents and point out the importance of
hidden strangeness in rendering the nucleon-like states heavier than the S=1
state. Using recent experimental data on a possible S=1 pentaquark state, we
make decay predictions for other members of the antidecuplet.Comment: 12 pages LaTeX, 1 eps figur
The fate of the homoctenids (Tentaculitoidea) during the Frasnian-Famennian mass extinction (Late Devonian)
The homoctenids (Tentaculitoidea) are small, conical-shelled marine animals which are amongst the most abundant and widespread of all Late Devonian fossils. They were a principal casualty of the Frasnian-Famennian (F-F, Late Devonian) mass extinction, and thus provide an insight into the extinction dynamics. Despite their abundance during the Late Devonian, they have been largely neglected by extinction studies. A number of Frasnian-Famennian boundary sections have been studied, in Poland, Germany, France, and the United States. These sections have yielded homoctenids, which allow precise recognition of the timing of the mass extinction. It is clear that the homoctenids almost disappear from the fossil record during the latest Frasnian “Upper Kellwasser Event”. The coincident extinction of this pelagic group, and the widespread development of intense marine anoxia within the water column, provides a causal link between anoxia and the F-F extinction. Most notable is the sudden demise of a group, which had been present in rock-forming densities, during this anoxic event. One new species, belonging to Homoctenus is described, but is not formally named here
Magnetic moments of exotic pentaquarks in the chiral quark-soliton model
We investigate the magnetic moments of the baryon antidecuplet within the
framework of the chiral quark-soliton model in the chiral limit in a
``\emph{model-independent}'' approach. Sum rules for the magnetic moments are
derived. The magnetic moment of is found to be about .Comment: 9 pages, 1 figure, submitted to Phys. Lett. B. The title was changed.
One sign mistake was removed with the text extended. One author is adde
Prospects for Pentaquark Production at Meson Factories
Following Rosner [hep-ph/0312269], we consider B-decay production channels
for the exotic I=0 and pentaquarks that have been recently reported. We
also discuss new search channels for isovector pentaquarks, such as the
, that are generically present in chiral soliton
models but were not observed in recent experiments. Futhermore, we argue that
weak decays of charmed baryons, such as the and ,
provide another clean way of detecting exotic baryons made of light quarks
only. We also discuss discovery channels for charmed pentaquarks, such as the
isosinglet , in weak decays of bottom mesons and
baryons. Finally, we discuss prospects for inclusive production of pentaquarks
in collisions, with associated production of particles carrying the
opposite baryon number.Comment: 15 pages, LaTeX; v2,v3: minor corrections, references added; v4:
minor modifications, the version published in Physics Letters
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
Flavored exotic multibaryons and hypernuclei in topological soliton models
The energies of baryon states with positive strangeness, or anti-charm
(-beauty) are estimated in chiral soliton approach, in the "rigid oscillator"
version of the bound state soliton model proposed by Klebanov and Westerberg.
Positive strangeness states can appear as relatively narrow nuclear levels
(Theta-hypernuclei), the states with heavy anti-flavors can be bound with
respect to strong interactions in the original Skyrme variant of the model (SK4
variant). The binding energies of anti-flavored states are estimated also in
the variant of the model with 6-th order term in chiral derivatives in the
lagrangian as solitons stabilizer (SK6 variant). The latter variant is less
attractive, and nuclear states with anti-charm or anti-beauty can be unstable
relative to strong interactions. The chances to get bound hypernuclei with
heavy antiflavors are greater within "nuclear variant" of the model with
rescaled model parameter (Skyrme constant e or e' decreased by ~30%) which is
expected to be valid for baryon numbers greater than B ~10. The rational map
approximation is used to describe multiskyrmions with baryon number up to ~30
and to calculate the quantities necessary for their quantization (moments of
inertia, sigma-term, etc.).Comment: 24 pages, 7 table
Pentaquark baryons in SU(3) quark model
We study the SU(3) group structure of pentaquark baryons which are made of
four quarks and one antiquark. The pentaquark baryons form {1}, {8}, {10},
{10}-bar, {27}, and {35} multiplets in SU(3) quark model. First, the flavor
wave functions of all the pentaquark baryons are constructed in SU(3) quark
model and then the flavor SU(3) symmetry relations for the interactions of the
pentaquarks with three-quark baryons and pentaquark baryons are obtained.Comment: REVTeX, 36 pages, 8 figures, references added, section for mass sum
rules is added, to appear in Phys. Rev.
Pentaquark baryon production at the Relativistic Heavy Ion Collider
Production of pentaquark baryons in central relativistic heavy ion
collisions is studied in a kinetic model. Assuming that a quark-gluon plasma is
produced in the collisions, we first determine the number of
produced from the quark-gluon plasma using a parton coalescence model, and then
take into consideration its production and absorption in subsequent hadronic
matter via the reactions ,
, and \piN\leftrightarrow\bar K\Theta. We find
that although the final number is affected by hadronic interactions,
it remains sensitive to the initial number of produced from the
quark-gluon plasma, particularly in the case of a small width as
imposed by the and scattering data. Because of small baryon
chemical potential in the hot dense matter produced in these collisions, the
number of produced anti- is only slightly smaller than that of
.Comment: 6 pages, 2 figures, revised version, to appear in PL
Partners of the Theta^+ in Large N_c QCD
A strangeness +1 exotic baryon Theta^+ has recently been seen in a number of
experiments. We demonstrate that in large N_c QCD the existence of such a state
implies the existence of S = +1 partner states with various spins and isospins
but comparable masses. We discuss the spectroscopy of such states and possible
channels in which they can be observed, based on the simple assumption that
those states with pentaquark quantum numbers are unlikely to be large N_c
artifacts.Comment: 5 pages, no figures, Revte
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