136 research outputs found
Negative parity pentaquarks in large Nc QCD and quark model
Recently, the 1/Nc expansion has been applied to the study of exotic baryons
containing both quarks and antiquarks. We extend this approach to exotic states
with mixed symmetric spin-flavor symmetry, which correspond in the quark model
to negative parity pentaquarks, and discuss the large Nc predictions for their
mass spectrum. The heavy exotics Qbar q^4 transform as 3, 6bar,15 and 15' under
flavor SU(3), while the light states include the exotic multiplets 10bar, 27,
35. We give mass relations among these multiplets following from the 1/Nc
expansion. In the quark model, the mass splittings between these states are
given by color-spin interactions. Using the observation of an anticharmed
exotic by the H1 collaboration, we give predictions for the masses of other
expected heavy pentaquarks.Comment: 18 pages, one figure, uses youngtab.sty; v3: eq.(40) corrected, final
version to appear in PR
Radiative Decays of the P-Wave Charmed Mesons
Minor (mainly numerical) corrections.Comment: 12 pages, LaTeX, MZ-TH/92-5
Improved variables for measuring the polarization
We discuss a few possible strategies for measuring the polarization of the
baryons produced in -annihilation at the
resonance through their inclusive semileptonic decays. After
reviewing the existing methods, a new method is proposed, based on the ratio of
the averages of the squared electron and neutrino energy, including both
perturbative and nonperturbative corrections. This variable minimizes the
statistical error on the polarization, while keeping the
systematic theoretical errors at the level of 1-2%. A number of other
polarization-sensitive variables are also discussed, such as averages of ratios
of the electron and neutrino energy and the distribution in the difference of
the electron and neutrino rapidities.Comment: 23 pages, 4 uuencoded figures, REVTe
New Relations for Excited Baryons in Large N_c QCD
We show that excited baryons in large N_c QCD form multiplets, within which
masses are first split at O(1/N_c). The dominant couplings of resonances to
various mesons are highly constrained: The N(1535) decays at leading 1/N_c
order exclusively to eta-N rather than pi-N, and vice versa for the N(1650).
This multiplet structure is reproduced by a simple large N_c quark model, well
studied in the literature, that describes resonances as single-quark
excitations.Comment: 4 pages, no figures, ReVTeX 4. Includes new discussion of previous
work on excited baryon tower
Decays of Non-strange Negative Parity Baryons in the 1/Nc Expansion
The decays of non-strange negative parity baryons via the emission of single
and mesons are analyzed in the framework of the expansion.
A basis of spin-flavor operators for the partial wave amplitudes is established
to order and the unknown effective coefficients are determined by
fitting to the S- and D-wave partial widths as provided by the Particle Data
Group. A set of relations between widths that result at the leading order, i.e.
order , is given and tested with the available data. Up to a few
exceptions, a good description of the partial decays widths is already obtained
at that order. Because of the rather large errors in the empirical input data
the next to leading order fit fails to pin down with satisfactory accuracy the
subleading effective coefficients. The hierarchy expected from the
expansion is reflected in the results.Comment: 24 pages, 8 table
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