1,278 research outputs found
Baryon resonances and strong QCD
Light-baryon resonances (with u,d, and s quarks in the SU(3) classification)
fall on Regge trajectories. When their squared masses are plotted against the
intrinsic orbital angular momenta {\rm L}, 's with even and odd
parity can be described by the same Regge trajectory. For a given {\rm L},
nucleon resonances with spin {\rm S}=3/2 are approximately degenerate in mass
with resonances. To which total angular momentum {\rm L} and {\rm S}
couple has no significant impact on the baryon mass. Nucleons with spin 1/2 are
shifted in mass; the shift is - in units of squared masses - proportional to
the component in the wave function which is antisymmetric in spin and flavor.
Based on these observations, a new baryon mass formula is proposed which
reproduces nearly all known baryon masses. It is shown that the masses are
compatible with a quark-diquark picture while the richness of the
experimentally known states require three particles to participate in the
dynamics. This conflict is resolved by proposing that quarks polarize the QCD
condensates and are surrounded by a polarization cloud shielding the color. A
new interpretation of constituent quarks as colored quark clusters emerges;
their interaction is responsible for the mass spectrum. Fast flavor exchange
between the colored quark clusters exhausts the dynamical richness of the
three-particle dynamics. The colored-quark-cluster model provides a mechanism
in which the linear confinement potential can be traced to the increase of the
volume in which the condensates are polarized. The quark-spin magnetic moment
induces currents in the polarized condensates which absorb the quark-spin
angular momentum: the proton spin is not carried by quark spins. The model
provides a new picture of hybrids and glueballs.Comment: 33 pages, 8 Figure
Classification of -Wave and Systems
An exotic meson, the with , has been seen to
decay into a p-wave system. If this decay conserves flavor SU(3),
then it can be shown that this exotic meson must be a four-quark state () belonging to a flavor representation
of SU(3). In contrast, the with a substantial decay mode into
is likely to be a member of a flavor octet.Comment: 8 page
Do parity doublets in the baryon spectrum reflect restoration of chiral symmetry?
We discuss the mass spectrum of highly-excited nucleon and
resonances. The spectrum exhibits parity doublets, pairs of resonances of
identical total angular momentum J but of opposite parity. It has been proposed
that the parity doublets evidence restoration of chiral symmetry at large
baryon excitation energies. We compare this conjecture with the possibility
that high-mass states are organized into -multiplets with defined
intrinsic quark spins and orbital angular momenta. Indeed, the latter
interpretation results in a better description of the data. There is however a
small and statisticially not very significant trend of the data which might
indicate that chiral symmetry is not yet restored but does influence the masses
of highly excited states.Comment: 10 pages, 1 fi
Baryon-baryon and baryon-antibaryon interaction amplitudes in the spin--momentum operator expansion method
Partial wave scattering amplitudes in baryon-baryon and baryon-antibaryon
collisions and amplitudes for the production and decay of baryon resonances are
constructed in the framework of the spin-momentum operator expansion method.
The approach is relativistically invariant and it allows us to perform combined
analyses of different reactions imposing analyticity and unitarity directly.
The role of final state interactions (triangle and box diagrams) is discussed.Comment: 23 pages, 10 figure
Vector mesons in systems
A new selection rule is described for the vector mesons in the decuplet
representations of flavor SU(3)Comment: 7 pages and 1 figur
Light Hadron Spectroscopy: Theory and Experiment
Rapporteur talk at the Lepton-Photon Conference, Rome, July 2001: reviewing
the evidence and strategies for understanding scalar mesons, glueballs and
hybrids, the gluonic Pomeron and the interplay of heavy flavours and light
hadron dynamics. Dedicated to the memory of Nathan Isgur, long-time
collaborator and friend, whose original ideas in hadron spectroscopy formed the
basis for much of the talk.Comment: to be published in "Lepton Photon 2001 Conference Proceedings" (World
Scientific Publishing), 19 pages with 6 figure
Large-scale albuminuria screen for nephropathy models in chemically induced mouse mutants
Background/Aim: Phenotype-driven screening of a great pool of randomly mutant mice and subsequent selection of animals showing symptoms equivalent to human kidney diseases may result in the generation of novel suitable models for the study of the pathomechanisms and the identification of genes involved in kidney dysfunction. Methods: We carried out a large-scale analysis of ethylnitrosourea (ENU)-induced mouse mutants for albuminuria by using qualitative SDS-polyacrylamide gel electrophoresis. Results: The primary albuminuria screen preceded the comprehensive phenotypic mutation analysis in a part of the mice of the Munich ENU project to avoid loss of mutant animals as a consequence of prolonged suffering from severe nephropathy. The primary screen detected six confirmed phenotypic variants in 2,011 G1 animals screened for dominant mutations and no variant in 48 G3 pedigrees screened for recessive mutations. Further breeding experiments resulted in two lines showing a low phenotypic penetrance of albuminuria. The secondary albuminuria screen was carried out in mutant lines which were established in the Munich ENU project without preceding primary albuminuria analysis. Two lines showing increased plasma urea levels were chosen to clarify if severe kidney lesions are involved in the abnormal phenotype. This analysis revealed severe albuminuria in mice which are affected by a recessive mutation leading to increased plasma urea and cholesterol levels. Conclusion: Thus, the phenotypic selection of ENU-induced mutants according to the parameter proteinuria in principle demonstrates the feasibility to identify nephropathy phenotypes in ENU-mutagenized mice. Copyright (C) 2005 S. Karger AG, Basel
Photoproduction of mesons off neutrons from a deuteron target
A formalism is developed for the partial wave analysis of data on meson
photoproduction off deuterons and applied to photoproduction of and
mesons. Different interpretations of a dip-bump structure of the
photoproduction cross section in the 1670 MeV region are presented and
discussed. Helicity amplitudes for two low-mass states are determined.Comment: 11 pages, 13 figure
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