1,878 research outputs found
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
Uncertainties in determining parton distributions at large x
We critically examine uncertainties in parton distribution functions (PDFs)
at large x arising from nuclear effects in deuterium F2 structure function
data. Within a global PDF analysis, we assess the impact on the PDFs from
uncertainties in the deuteron wave function at short distances and nucleon
off-shell effects, the use of relativistic kinematics, as well as the use of
less a restrictive parametrization of the d/u ratio. We find that in particular
the d-quark and gluon PDFs vary significantly with the choice of nuclear model.
We highlight the impact of these uncertainties on the determination of the
neutron structure function, and on W boson production and parton luminosity at
the Tevatron and the LHC. Finally, we discuss prospects for new measurements
sensitive to the d-quark and gluon distributions but insensitive to nuclear
corrections.Comment: 37 pages, 13 figures. Final published versio
New parton distributions from large-x and low-Q^2 data
We report results of a new global next-to-leading order fit of parton
distribution functions in which cuts on W and Q are relaxed, thereby including
more data at high values of x. Effects of target mass corrections (TMCs),
higher twist contributions, and nuclear corrections for deuterium data are
significant in the large-x region. The leading twist parton distributions are
found to be stable to TMC model variations as long as higher twist
contributions are also included. The behavior of the d quark as x-->1 is
particularly sensitive to the deuterium corrections, and using realistic
nuclear smearing models the d-quark distribution at large x is found to be
softer than in previous fits performed with more restrictive cuts.Comment: 31 pages, 8 figures. Minor corrections. References added. To appear
in Phys.Rev.
Global Analysis of Data on the Proton Structure Function g1 and Extraction of its Moments
Inspired by recent measurements with the CLAS detector at Jefferson Lab, we
perform a self-consistent analysis of world data on the proton structure
function g1 in the range 0.17 < Q2 < 30 (GeV/c)**2. We compute for the first
time low-order moments of g1 and study their evolution from small to large
values of Q2. The analysis includes the latest data on both the unpolarized
inclusive cross sections and the ratio R = sigmaL / sigmaT from Jefferson Lab,
as well as a new model for the transverse asymmetry A2 in the resonance region.
The contributions of both leading and higher twists are extracted, taking into
account effects from radiative corrections beyond the next-to-leading order by
means of soft-gluon resummation techniques. The leading twist is determined
with remarkably good accuracy and is compared with the predictions obtained
using various polarized parton distribution sets available in the literature.
The contribution of higher twists to the g1 moments is found to be
significantly larger than in the case of the unpolarized structure function F2.Comment: 18 pages, 13 figures, to appear in Phys. Rev.
Perturbative QCD Analysis of Local Duality in a fixed W^2 Framework
We study the global Q^2 dependence of large x, F_2 nucleon structure function
data, with the aim of providing a perturbative-QCD based, quantitative analysis
of parton-hadron duality. As opposed to previous analyses at fixed x, we use a
framework in fixed W^2. We uncover a breakdown of the twist-4 approximation
with a renormalon type improvement at O(1/Q^4) which, by affecting the initial
evolution of parton distributions, will have consequences for pQCD analyses
also at large x and very large Q^2.Comment: RevTex4, 8 pages, 3 figure
The impact of new neutrino DIS and Drell-Yan data on large-x parton distributions
New data sets have recently become available for neutrino and antineutrino
deep inelastic scattering on nuclear targets and for inclusive dimuon
production in pp pd interactions. These data sets are sensitive to different
combinations of parton distribution functions in the large-x region and,
therefore, provide different constraints when incorporated into global parton
distribution function fits. We compare and contrast the effects of these new
data on parton distribution fits, with special emphasis on the effects at large
x. The effects of the use of nuclear targets in the neutrino and antineutrino
data sets are also investigated.Comment: 24 pages, 13 figure
Light-front CQM calculations of baryon electromagnetic form factors
The parameter-free predictions for the and electromagnetic transition form factors, obtained within our
light-front constituent quark model using eigenfunctions of a baryon mass
operator which includes a large amount of configuration mixing, are reported.
The effects due to small components in the baryon wave functions, such as S'-
and D-wave, are also investigated.Comment: to appear in the Proceedings of the International Workshop on Hadron
Dynamics with the new DAPHNE and CEBAF facilities, Frascati, Italy, 11-14
November 199
Особенности моделирования прогнозных оценок экономических объектов
Теория и практика экономических исследований свидетельствует о том, что моделирование прогнозных оценок будущего состояния экономических объектов является наиболее успешным только в тех случаях, когда модель в полной мере отражает как природу процесса управления, так и специфику деловой среды, то есть речь идет, по сути, об адекватности используемой модели
Global Analysis of Data on the Proton Structure Function g₁ and the Extraction of its Moments
Inspired by recent measurements with the CLAS detector at Jefferson Lab, we perform a self-consistent analysis of world data on the proton structure function g1 in the range 0.17 \u3c Q2 \u3c 30 (GeV/c)2. We compute for the first time low-order moments of g, and study their evolution from small to large values of Q2. The analysis includes the latest data on both the unpolarized inclusive cross sections and the ratio R = σ L/σT from Jefferson Lab, as well as a new model for the transverse asymmetry A2 in the resonance region. The contributions of both leading and higher twists are extracted, taking into account effects from radiative corrections beyond the next-to-leading order by means of soft-gluon resummation techniques. The leading twist is determined with remarkably good accuracy and is compared with the predictions obtained using various polarized parton distribution sets available in the literature. The contribution of higher twists to the g1 moments is found to be significantly larger than in the case of the unpolarized structure function F2
A Review of Target Mass Corrections
With recent advances in the precision of inclusive lepton--nuclear scattering
experiments, it has become apparent that comparable improvements are needed in
the accuracy of the theoretical analysis tools. In particular, when extracting
parton distribution functions in the large-x region, it is crucial to correct
the data for effects associated with the nonzero mass of the target. We present
here a comprehensive review of these target mass corrections (TMC) to structure
functions data, summarizing the relevant formulas for TMCs in electromagnetic
and weak processes. We include a full analysis of both hadronic and partonic
masses, and trace how these effects appear in the operator product expansion
and the factorized parton model formalism, as well as their limitations when
applied to data in the x->1 limit. We evaluate the numerical effects of TMCs on
various structure functions, and compare fits to data with and without these
corrections.Comment: 41 pages, 13 figures; minor updates to match published versio
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