690 research outputs found
Experimental moments of the nucleon structure function F2
Experimental data on the F2 structure functions of the proton and deuteron,
including recent results from CLAS at Jefferson Lab, have been used to
construct their n<=12 moments. A comprehensive analysis of the moments in terms
of the operator product expansion has been performed to separate the moments
into leading and higher twist contributions. Particular attention was paid to
the issue of nuclear corrections in the deuteron, when extracting the neutron
moments from data. The difference between the proton and neutron moments was
compared directly with lattice QCD simulations. Combining leading twist moments
of the neutron and proton we found the d/u ratio at x->1 approaching 0,
although the precision of the data did not allow to exclude the 1/5 value. The
higher twist components of the proton and neutron moments suggest that
multi-parton correlations are isospin independent.Comment: Proceedings of 13th International QCD Conference (QCD 06),
Montpellier, France, July 3-7th 200
Proton and neutron polarized structure functions from low to high Q**2
Phenomenological parameterizations of proton and neutron polarized structure
functions, g1p and g1n, are developed for x > 0.02 using deep inelastic data up
to ~ 50 (GeV/c)**2 as well as available experimental results on photo- and
electro-production of nucleon resonances. The generalized Drell-Hearn-Gerasimov
sum rules are predicted from low to high values of Q**2 and compared with
proton and neutron data. Furthermore, the main results of the power correction
analysis carried out on the Q**2-behavior of the polarized proton Nachtmann
moments, evaluated using our parameterization of g1p, are briefly summarized.Comment: Proceedings of the II International Symposium on the
Gerasimov-Drell-Hearn sum rule and the spin structure of the nucleon, Genova
(Italy), July 3-6, 200
Neutron structure function moments at leading twist
The experimental data on F2 structure functions of the proton and deuteron
were used to construct their moments. In particular, recent measurements
performed with CLAS detector at Jefferson Lab allowed to extend our knowledge
of structure functions in the large-x region. The phenomenological analysis of
these experimental moments in terms of the Operator Product Expansion permitted
to separate the leading and higher twist contributions. Applying nuclear
corrections to extracted deuteron moments we obtained the contribution of the
neutron. Combining leading twist moments of the neutron and proton we found d/u
ratio at x->1 approaching 0, although 1/5 value could not be excluded. The
twist expansion analysis suggests that the contamination of higher twists
influences the extraction of the d/u ratio at x->1 even at Q2-scale as large as
12 (GeV/c)^2.Comment: To appear in proceedings of Quark Confinement and the Hadron Spectrum
VII Conference, Ponta Delgada, Portugal, 2-7 September 200
The proton structure function F2 in the resonance region
Unique measurement of the proton structure function F2 in a wide
two-dimensional region of x and Q**2 has been reported. The accessible
kinematics covers entire resonance region up to W=2.5 GeV in the Q**2 interval
from 0.1 to 4.5 GeV**2. Obtained data allowed for the first time an evaluation
of moments of the structure function F2 directly from experimental data as well
as an intensive study of the Bloom-Gilman duality phenomenon.Comment: 6 pages, 4 figures, Proceedings of GDH2002 Conference, 3-6 July 2002,
Genova, Italy, to be published in World Scientifi
Neutron spectrometer for fast nuclear reactors
In this paper we describe the development and first tests of a neutron
spectrometer designed for high flux environments, such as the ones found in
fast nuclear reactors. The spectrometer is based on the conversion of neutrons
impinging on Li into and whose total energy comprises the
initial neutron energy and the reaction -value. The LiF layer is
sandwiched between two CVD diamond detectors, which measure the two reaction
products in coincidence. The spectrometer was calibrated at two neutron
energies in well known thermal and 3 MeV neutron fluxes. The measured neutron
detection efficiency varies from 4.2 to 3.5 for
thermal and 3 MeV neutrons, respectively. These values are in agreement with
Geant4 simulations and close to simple estimates based on the knowledge of the
Li(n,) cross section. The energy resolution of the spectrometer
was found to be better than 100 keV when using 5 m cables between the detector
and the preamplifiers.Comment: submitted to NI
Self-Consistent Data Analysis of the Proton Structure Function g1 and Extraction of its Moments
The reanalysis of all available world data on the longitudinal asymmetry A||
is presented. The proton structure function g1 was extracted within a unique
framework of data inputs and assumptions. These data allowed for a reliable
evaluation of moments of the structure function g1 in the Q2 range from 0.2 up
to 30 GeV2. The Q2 evolution of the moments was studied in QCD by means of
Operator Product Expansion (OPE).Comment: Proceeding of 3rd International Symposium on the
Gerasimov-Drell-Hearn Sum Rule and its extensions, Old Dominion University,
Norfolk, Virginia June 2-5, 200
Leading twist moments of the neutron structure function F2n
We perform a global analysis of neutron F2n structure function data, obtained
by combining proton and deuteron measurements over a large range of kinematics.
From these data the lowest moments (n <= 10) of the leading twist neutron F2n
structure function are extracted. Particular attention is paid to nuclear
effects in the deuteron, which become increasingly important for the higher
moments. Our results for the nonsinglet, 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: 34 pages, 13 figures. Minor changes. Version to appear in NP
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