77 research outputs found
Positive parity pentaquark towers in large Nc QCD
We construct the complete set of positive parity pentaquarks, which
correspond in the quark model to {\bar s} q^{Nc+1} states with one unit of
orbital angular momentum L=1. In the large Nc limit they fall into the K=1/2
and K=3/2 irreps (towers) of the contracted SU(4)c symmetry. We derive
predictions for the mass spectrum and the axial couplings of these states at
leading order in 1/Nc. The strong decay width of the lowest-lying positive
parity exotic state is of order O(1/Nc), such that this state is narrow in the
large Nc limit. Replacing the antiquark with a heavy antiquark {\bar Q}
q^{Nc+1}, the two towers become degenerate, split only by O(1/mQ) hyperfine
interactions. We obtain predictions for the strong decay widths of heavy
pentaquarks to ordinary baryons and heavy H(*)_{\bar Q} mesons at leading order
in 1/Nc and 1/mQ.Comment: 21 pages, 2 figures, 5 table
A comprehensive search for the \Theta^+ pentaquark on the lattice
We study spin 1/2 isoscalar and isovector, even and odd parity candidates for
the pentaquark particle using large scale lattice QCD
simulations. Previous lattice works led to inconclusive results because so far
it has not been possible to unambiguously identify the known scattering
spectrum and tell whether additionally a genuine pentaquark state also exists.
Here we carry out this analysis using several possible wave functions
(operators). Linear combinations of those have a good chance of spanning both
the scattering and pentaquark states. Our operator basis is the largest in the
literature, and it also includes spatially non-trivial ones with unit orbital
angular momentum. The cross correlator we compute is 1414 with 60
non-vanishing elements. We can clearly distinguish the lowest scattering
state(s) in both parity channels up to above the expected location of the
pentaquark, but we find no trace of the latter. Based on that we conclude that
there are most probably no pentaquark bound states at our quark masses,
corresponding to =400--630 MeV. However, we cannot rule out the
existence of a pentaquark state at the physical quark mass corresponding to
=135 MeV or pentaquarks with a more exotic wave function.Comment: 18 pages, 2 figure
Magnetic moment of the pentaquark with light-cone QCD sum rules
In this article, we study the magnetic moment of the pentaquark state as diquark-diquark-antiquark () state in the
framework of the light-cone QCD sum rules approach. The numerical results
indicate the magnetic moment of the pentaquark state is about
.Comment: 10 pages, 1 figure. The main contents of this article is included in
hep-ph/0503007, this article will not be submitted to a journal for
publicatio
Quark-model study of few-baryon systems
We review the application of non-relativistic constituent quark models to
study one, two and three non-strange baryon systems. We present results for the
baryon spectra, potentials and observables of the NN, N,
and NN systems, and also for the binding energies of three
non-strange baryon systems. We make emphasis on observable effects related to
quark antisymmetry and its interplay with quark dynamics.Comment: 82 pages, 36 figures, 18 tables. Accepted for publication in Reports
on Progress in Physic
Polarization phenomena in open charm photoproduction processes
We analyze polarization effects in associative photoproduction of
pseudoscalar () charmed mesons in exclusive processes , , . Circularly polarized photons
induce nonzero polarization of the -hyperon with - and -components
(in the reaction plane) and non vanishing asymmetries and for polarized nucleon target. These polarization observables can be
predicted in model-independent way for exclusive -production processes
in collinear kinematics. The T-even -polarization and asymmetries for
non-collinear kinematics can be calculated in framework of an effective
Lagrangian approach. The depolarization coefficients , characterizing
the dependence of the -polarization on the nucleon polarization are also
calculated.Comment: 36 pages 13 figure
Observation of narrow baryon resonance decaying into in pA-interactions at with SVD-2 setup
SVD-2 experiment data have been analyzed to search for an exotic baryon
state, the -baryon, in a decay mode at on IHEP
accelerator. The reaction with a limited multiplicity was
used in the analysis. The invariant mass spectrum shows a resonant
structure with and . The statistical significance of this peak was estimated to be of . The mass and width of the resonance is compatible with the recently
reported - baryon with positive strangeness which was predicted as an
exotic pentaquark () baryon state. The total cross section for
production in pN-interactions for was estimated to be
and no essential deviation from A-dependence for inelastic
events was found.Comment: 8 pages, 7 figures, To be submitted to Yadernaya Fizika. v3-v5 - Some
references added, minor typos correcte
Search for a strongly decaying neutral charmed pentaquark
We present a search for a charmed pentaquark decaying strongly to
. Finding no evidence for such a state, we set limits on the cross
section times branching ratio relative to and under particular
assumptions about the production mechanism.Comment: To be published in Physics Letters
Atmospheric Muon Flux at Sea Level, Underground, and Underwater
The vertical sea-level muon spectrum at energies above 1 GeV and the
underground/underwater muon intensities at depths up to 18 km w.e. are
calculated. The results are particularly collated with a great body of the
ground-level, underground, and underwater muon data. In the hadron-cascade
calculations, the growth with energy of inelastic cross sections and pion,
kaon, and nucleon generation in pion-nucleus collisions are taken into account.
For evaluating the prompt muon contribution to the muon flux, we apply two
phenomenological approaches to the charm production problem: the recombination
quark-parton model and the quark-gluon string model. To solve the muon
transport equation at large depths of homogeneous medium, a semi-analytical
method is used. The simple fitting formulas describing our numerical results
are given. Our analysis shows that, at depths up to 6-7 km w. e., essentially
all underground data on the muon intensity correlate with each other and with
predicted depth-intensity relation for conventional muons to within 10%.
However, the high-energy sea-level data as well as the data at large depths are
contradictory and cannot be quantitatively decribed by a single nuclear-cascade
model.Comment: 47 pages, REVTeX, 15 EPS figures included; recent experimental data
and references added, typos correcte
Possibility of determinig the parity of the pentaquark from photoproduction near threshold
We discuss the possibility of determining the parity of the baryon
from photoproduction process near threshold. We utilize
the conservation laws of parity and angular momentum for the analysis of
angular distributions and spin observables near threshold. Since the discussion
is in essence a partial wave analysis of the production mechanism the result
should be less dependent on the model parameters. Our analysis shows that the
angular distribution and photon polarization asymmetry for the process of
neutron target are sensitive to the parity of the , but not for the
case of proton target. In the case of proton target, the polarization
asymmetries of target and recoiled are preferred for parity
determination.Comment: 23 pages, 13 figures, extended versio
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