59 research outputs found
Inclusive Charmed-Baryon Decays and Lifetimes
We have quantitatively reanalyzed the inclusive charmed-baryon decays. New
ingredients are the Voloshin preasymptotic effects in semileptonic decays and
the Cabibbo-subleading contributions to both semileptonic and nonleptonic
decays. It has been found that the Cabbibo-subleading Voloshin contribution
essentially improves the theoretical semileptonic branching ratio of
, in agreement with experiment. The semileptonic branching
ratios for and are found to be large, i.e., of the
order of 20%. The lifetimes hierarchy is in a good qualitative and even
quantitative agreement with experiment except for the lifetime,
which is somewhat smaller than the experimental value. Future measurements,
especially measurements of the semileptonic branching ratios for
, and should be decisive for the check of
this approach.Comment: 13 pages, Latex, 3 figures included, shortened version, to appear in
Z.Phys.
Preasymptotic effects in beauty decays
Large preasymptotic effects in beauty decays have been found using
heavy-quark and SU(3) symmetry, as well as experimental data on charmed
hyperons. Contrary to rather uniform beauty-meson lifetimes, a much larger
spread of beauty-baryon lifetimes is predicted. However, it is highly unlikely
that, theoretically, the ratio, which at
present deviates more than from the experimental result, can be
lowered below 0.9.Comment: 6 pages, talk given by B. Melic at The 3rd International Conference
on B Physics and CP Violation, Taipei, Taiwan, December 3-7, 1999, to appear
in the Proceedings, two figures adde
Inclusive decays and lifetimes of doubly charmed baryons
The analysis of singly charmed hadrons has been extended to the case of
doubly charmed baryons, , and .
Doubly charmed baryons are described as a system containing a heavy
-diquark and a light quark, similarly as in a heavy-light meson. This leads
to preasymptotic effects in semileptonic and nonleptonic decays which are
essentially proportional to the meson wave function. Interplay between
preasymptotic effects in semileptonic and/or nonleptonic decay rates leads to
very clear predictions for semileptonic branching ratios and lifetimes of
doubly charmed baryons.Comment: 14 pages latex file, 4 figures, 1 tabl
Nucleon strangeness as the response to a strangeness-sensitive probe in a class of hadron models
On top of its valence quarks, the full nucleon ground state may contain
appreciable admixture of s-\bar{s} pairs already at small momentum transfers.
This paper discusses strangeness in the mean-field type of nucleon models, and
exemplifies this by explicit calculations in the MIT bag model enriched by the
presence of instantons.
We calculate the instanton contribution to the strangeness in the MIT bag (on
top of the standard contribution to strangeness found in that model). Although
we do it in an essentially perturbative way, we present a detailed derivation
of the formula expressing nucleon matrix elements of bilinear strange quark
operators, in terms of a model valence nucleon state and interactions producing
quark-antiquark fluctuations on top of that valence state. We do it in detail
to clarify our argument that in the context of the mean-field type of quark
models (where a Fock state expansion exists and where the nucleon state can be
constructed out of single-quark states), the resulting formula acquires a
significance beyond perturbation theory.The derivation combines the usage of
the evolution operator containing a strangeness source, and Feynman-Hellmann
theorem.Comment: LaTeX2e, 34 pages, 4 figures (included
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