187 research outputs found
Production of Theta+ in gamma + D -> Lambda + Theta+ and gamma + D -> Sigma + Theta+ reactions
The gamma + D -> Lambda + Theta+ and gamma + D -> Sigma + Theta+ reactions
can be used to determine the width of Theta+ almost model-independently. We
calculate the differential cross sections of the gamma +D -> Lambda + Theta+,
gamma + D -> Sigma + Theta+ and relevant background reactions in the photon
energy range 1.2 < E_{\gamma} < 2.6 GeV. We determine the most favorable
kinematic conditions and observables for the experimental studies of Theta+ in
the considered processes. We argue that a comparison of the gamma + D -> Lambda
+ Theta+ and gamma + D -> Sigma + Theta+ cross sections should unambiguously
determine isospin of Theta+.Comment: 22 pages, 9 figures. Final published versio
Evidence for formation of a narrow pKshort resonance with mass near 1533 MeV in neutrino interactions
A narrow baryon resonance is observed in invariant mass of the pKshort system
formed in neutrino and antineutrino collisions with nuclei. The mass of the
resonance is estimated as (1533+-5)MeV. The observed width is less than 20 MeV,
and is compatible with being entirely due to experimental resolution. The
statistical significance of the signal is near 6.7 standard deviations. As the
position of the observed resonance does not match the mass of any known
\Sigma^{*+} state, we believe that it arises from neutrino production of the
\Theta^+ pentaquark baryon. The analysis is based on the data obtained in past
neutrino experiments with big bubble chambers: WA21, WA25, WA59, E180 and E632.Comment: Institute of Theoretical and Experimental Physics, B.Cheremyshkinskya
25, Moscow 117259, Russi
A Selection Rule for Multiquark Decays
By assuming SU(6)_cs symmetry for pentaquark decays one finds a selection
rule, which strongly reduces the number of states able to decay into a baryon
and a meson final state and allows an intriguing identification for the Theta^+
particle recently discovered with the prediction of a narrow width.Comment: 10 pages, no figure
The pentaquark in K-plus-d total cross section data
An analysis of -d total cross section data is undertaken to explore
possible effects of the recently observed resonance in the S=+1 hadronic system
with mass around 1.55 GeV. It is found that a structure corresponding to the
resonance is visible in the data. The width consistent with the observed
deviation from background is found to be MeV and the mass is
GeV/c for spin-parity \h^+ and \
GeV/c for \h^-. The errors are one standard deviation and statistical
only.
\Comment: 10 pages, 5 figures Replaced to correct references, add and correct
text. No change in content. More discussion of errors, increased error on
width, corrected one figur
Pentaquark Masses in Chiral Perturbation Theory
Heavy baryon chiral perturbation theory for pentaquarks is applied beyond
leading order. The mass splitting in the pentaquark anti-decuplet is calculated
up to NNLO. An expansion in the coupling of pentaquarks to non-exotic baryons
simplifies calculations and makes the pentaquark masses insensitive to the
pentaquark-nucleon mass difference. The possibility of determining coupling
constants in the chiral Lagrangian on the lattice is discussed. Both positive
and negative parities are considered.Comment: 11 pages; reference added, minor changes in wordin
Spin observables and the determination of the parity of in photoproduction reactions
Spin observables in the photoproduction of the are explored for
the purpose of determining the parity of the . Based on reflection
symmetry in the scattering plane, we show that certain spin observables in the
photoproduction of the can be related directly to its parity. We
also show that measurements of both the target nucleon asymmetry and the polarization may be useful in determining the parity of in
a model-independent way. Furthermore, we show that no combination of spin
observables involving only the polarization of the photon and/or nucleon in the
initial state can determine the parity of unambiguously.Comment: LaTeX, 11 pages, minor revisio
Absence of evidence for pentaquarks on the lattice
We study the question of whether or not QCD predicts a pentaquark state. We
use the improved, fixed point lattice QCD action which has very little
sensitivity to the lattice spacing and also allows us to reach light quark
masses. The analysis was performed on a single volume of size with lattice spacing of fm. We use the
correlation matrix method to identify the ground and excited states in the
isospin 0, negative parity channel. In the quenched approximation where
dynamical quark effects are omitted, we do not find any evidence for a
pentaquark resonance in QCD.Comment: 17 pages, 5 figures replaced with revised versio
Resonances, and mechanisms of Theta-production
After explaining necessity of exotic hadrons, we discuss mechanisms which
could determine production of the exotic Theta-baryon. A possible important
role of resonances (producing the Theta in real or virtual decays) is
emphasized for various processes. Several experimental directions for studies
of such resonances, and the Theta itself, are suggested. We briefly discuss
also recent negative results on the Theta-baryon.Comment: 6 page
- âŠ