116 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
Evolution of microstructure in advanced ferritic-martensitic steels under irradiation : the origin of low temperature radiation embrittlement
Advanced reduced activation ferritic/martensitic steels and oxide dispersion-strengthened steels exhibit significant radiation embrittlement under low temperature neutron irradiation. In this study we focused on atom probe tomography (APT) of Eurofer97 and ODS Eurofer steels irradiated with neutrons and heavy ions at low temperatures. Previous TEM studies revealed dislocation loops in the neutron-irradiated f\m steels. At the same time, our APT showed early stages of solid solution decomposition. High density (10 m) of ∼3–5 nm clusters enriched in chromium, manganese, and silicon atoms were found in Eurofer 97 irradiated in BOR-60 reactor to 32 dpa at 332°C. In this steel irradiated with Fe ions up to the dose of 24 dpa, pair correlation functions calculated using APT data showed the presence of Cr-enriched pre-phases.
APT study of ODS Eurofer found a significant change in the nanocluster composition after neutron irradiation to 32 dpa at 330 °C and an increase in cluster number density. APT of ODS steels irradiated with Fe ions at low temperatures revealed similar changes in nanoclusters.
These results suggest that irradiation-induced nucleation and evolution of very small precipitates may be the origin of low temperature radiation embrittlement of f\m steels
Effect of heavy-ion irradiation on the nanoscale state of advanced reactor ferritic-martensitic steels
Beyond CP violation: hadronic physics at BaBar
I report on recent studies of hadronic physics performed by the BaBar
Collaboration. Emphasis is given to the measurement of the properties of newly
discovered charmed hadrons and to the searches for light and heavy pentaquarks.Comment: 14 pages, 20 postscript figues, contributed to the Proceedings of the
First APS Topical Group Meeting on Hadron Physics, Fermilab, Batavia, IL
(October 24-26, 2004
Properties of Neutral Charmed Mesons in Proton--Nucleus Interactions at 70 GeV
The results of treatment of data obtained in the SERP-E-184experiment
"Investigation of mechanisms of the production of charmed particles in
proton-nucleus interactions at 70 GeV and their decays" by irradiating the
active target of the SVD-2 facility consisting of carbon, silicon, and lead
plates, are presented. After separating a signal from the two-particle decay of
neutral charmed mesons and estimating the cross section for charm production at
a threshold energy {\sigma}(c\v{c})=7.1 \pm 2.4(stat.) \pm 1.4(syst.)
\mub/nucleon, some properties of D mesons are investigated. These include the
dependence of the cross section on the target mass number (its A dependence);
the behavior of the differential cross sections d{\sigma}/dpt2 and
d{\sigma}/dxF; and the dependence of the parameter {\alpha} on the kinematical
variables xF, pt2, and plab. The experimental results in question are compared
with predictions obtained on the basis of the FRITIOF7.02 code.Comment: 9 pages, 9 figures,3 table
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
Improved study of a possible Theta+ production in the pp -> p K0 sigma+ reaction with the COSY-TOF spectrometer
The pp -> p K0 Sigma+ reaction was investigated with the TOF spectrometer at
COSY at 3.059 GeV/c incident beam momentum. The main objective was to clarify
whether or not a narrow exotic S = +1 resnance, the Theta+ pentaquark, is
populated at 1.53 GeV/c2 in the K0 p subsystem with a data sample of much
higher statistical significance compared to the previously reported data in
this channel. An analysis of these data does not confirm the existence of the
Theta+ pentaquark. This is expressed as an upper limit for the cross section
sigma (pp -> p K0 Sigma+) < 0.15 microbarn at the 95 percent confidence level.Comment: 11 pages, 5 figure
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