732 research outputs found
Leading and higher twists in proton, neutron and deuteron unpolarized structure functions
We summarize the results of a recent global analysis of proton and deuteron
F2 structure function world data performed over a large range of kinematics,
including recent measurements done at JLab with the CLAS detector. From these
data the lowest moments (n <= 10) of the unpolarized structure functions are
determined with good statistics and systematics. The Q**2 evolution of the
extracted moments is analyzed in terms of an OPE based twist expansion, taking
into account soft-gluon effects at large x. A clean separation among the
Leading and Higher-Twist terms is achieved. By combining proton and deuteron
measurements the lowest moments of the neutron F2 structure function are
determined and its leading twist term is extracted. Particular attention is
paid to nuclear effects in the deuteron, which become increasingly important
for the higher moments. Our results for the non-singlet, isovector (p - n)
combination of the leading twist moments are used to test recent lattice
simulations. We also determine the lowest few moments of the higher twist
contributions, and find these to be approximately isospin independent,
suggesting the possible dominance of ud correlations over uu and dd in the
nucleon.Comment: 8 pages, 4 figures; to appear in the Proceedings of the IVth
International Conference on Quark and Nuclear Physics (QNP06), Madrid
(Spain), June 5-10, 200
Isgur-Wise form factors of heavy baryons within a light-front constituent quark model
The space-like elastic form factors of baryons containing a heavy quark are
investigated within a light-front constituent quark model in the limit of
infinite heavy-quark mass, adopting a gaussian-like ansatz for the three-quark
wave function. The results obtained for the Isgur-Wise form factors
corresponding both to a spin-0 and a spin-1 light spectator pair are presented.
It is found that the Isgur-Wise functions depend strongly on the baryon
structure, being sharply different in case of diquark-like or collinear-type
configurations in the three-quark system. It is also shown that the
relativistic effects lead to a saturation property of the form factors as a
function of the baryon size. Our results are compared with those of different
models as well as with recent predictions from QCD sum rules and lattice QCD
simulations; the latter ones seem to suggest the dominance of collinear-type
configurations, in which the heavy-quark is sitting close to the center-of-mass
of the light quark pair.Comment: latex, 15 pp., 6 figures with epsfig.st
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